activates====10509564_155871_5594==>Similar findings have been achieved in another study , where it was further shown that <PROT1_155871>  Tat </PROT1_155871> activates the <PROT2_5594>  ERK </PROT2_5594> kinases ( TARGET_CITATION ) . ||10509564_155871_5594==>Because the full - length HIV - 1 <PROT1_155871>  Tat </PROT1_155871> protein is a known transactivator of viral gene expression and activates JNK and <PROT2_5594>  ERK </PROT2_5594> MAPK in CD4 T cells ( TARGET_CITATION ) , we included Tat48 & # x2013 ; 57 as a control peptide in all experiments . ||10509564_155871_5599==>Because the full - length HIV - 1 <PROT1_155871>  Tat </PROT1_155871> protein is a known transactivator of viral gene expression and activates <PROT2_5599>  JNK </PROT2_5599> and ERK MAPK in CD4 T cells ( TARGET_CITATION ) , we included Tat48 & # x2013 ; 57 as a control peptide in all experiments . ||10644332_155871_3725==>In this regard , Lim et al. have recently found that <PROT1_155871>  Tat </PROT1_155871> interaction with SP1 at the human monocyte chemoattractant protein 1 ( hMCP - 1 ) gene promoter may serve as a platform to recruit and stabilize the interaction of <PROT2_3725>  AP1 </PROT2_3725> and NF - { kappa } B proteins to this promoter ( TARGET_CITATION ) . ||10644332_155871_6667==>In this regard , Lim et al. have recently found that <PROT1_155871>  Tat </PROT1_155871> interaction with <PROT2_6667>  SP1 </PROT2_6667> at the human monocyte chemoattractant protein 1 ( hMCP - 1 ) gene promoter may serve as a platform to recruit and stabilize the interaction of AP1 and NF - { kappa } B proteins to this promoter ( TARGET_CITATION ) . ||10644332_155871_6667==><PROT1_155871>  Tat </PROT1_155871> enhances <PROT2_6667>  Sp1 </PROT2_6667> DNA binding and augments <PROT2_6667>  Sp1 </PROT2_6667> phosphorylation , which was shown to be associated with enhanced promoter activity ( CITATION , TARGET_CITATION ) . ||10644332_155871_6667==>Lim and Garzino - Demo provided evidence that ectopic expression of <PROT1_155871>  Tat </PROT1_155871> in the human astrocytoma cell line U - 89 triggered MCP - 1 expression and that this phenomenon relied on the synergistic action of <PROT2_6667>  Sp1 </PROT2_6667> , AP - 1 , and NF - kappa B ( TARGET_CITATION ) . ||11044099_155871_5595==>In an earlier study , we showed that , downstream of the PKC , <PROT1_155871>  Tat </PROT1_155871> could induce the phosphorylation of <PROT2_5595>  ERK1 </PROT2_5595> / 2 , an activation involved in <PROT1_155871>  Tat </PROT1_155871> - induced IL - 10 production ( 7 ) TARGET_CITATION . According to the literature PKC - { delta } , or even PKC - & # 223 ; II , is a potential candidate . ||11156964_155871_5294==>HIV - 1 - <PROT1_155871>  Tat </PROT1_155871> protein has been shown to down - regulate cAMP - response element - binding protein transcription factor expression in PC12 neuronal cells through <PROT2_5294>  PI3K </PROT2_5294> / AKT / cyclic nucleoside phosphodiesterase pathway ( TARGET_CITATION ) . ||11409852_155871_5594==>The mechanisms for ERK1 / 2 activation following viral infection may be induced by direct virus - receptor binding , such as for HIV activation of <PROT2_5594>  ERK </PROT2_5594> ( CITATION ) , or by exposure to a viral protein such as the hepatitis C virus core protein ( CITATION ) or HIV <PROT1_155871>  Tat </PROT1_155871> protein ( TARGET_CITATION ) . ||12023963_155871_5599==>SURE Escherichia coli ( Stratagene ) was transformed with pGEX - 2TK , pGEX - <PROT1_155871>  Tat </PROT1_155871> - 86 , pGEX - <PROT1_155871>  Tat </PROT1_155871> C ( 22 , 25 , 27 ) A , or pGEX - <PROT1_155871>  Tat </PROT1_155871> R ( 49 , 52 , 53 , 55 , 56 , 57 ) A and was induced with IPTG ( isopropyl - & # 223 ; - D - thiogalactopyranoside ) for 3 to 4 h at 37 & # 176 ; C , and the fusion proteins were extracted as previously described ( CITATION , TARGET_CITATION ) , keeping all solutions degassed and at 4 & # 176 ; c. The yield , stability , and biological activity of wild - type <PROT1_155871>  Tat </PROT1_155871> ( assessed as activation of endothelial cell c - Jun N - terminal kinase ( <PROT2_5599>  JNK </PROT2_5599> ) ) were highest when flash - frozen as a glutathione S - transferase ( GST ) fusion . ||12167619_155871_5594==>In this context , it is worth noting that HIV - 1 <PROT1_155871>  Tat </PROT1_155871> protein activates the <PROT2_5594>  ERK </PROT2_5594> pathway ( TARGET_CITATION ) . ||12573582_1026_155807==>Preliminary studies in our laboratory indicate that <PROT2_155807>  Vpr </PROT2_155807> may be responsible , at least in part , for the enhanced expression of macrophage <PROT1_1026>  p21 </PROT1_1026> ( n. V & aacute ; zquez et al. , unpublished observations ) , as recently suggested in T lymphoid and myeloid cell lines ( TARGET_CITATION ) . ||9325171_155871_5594==>In this respect , <PROT1_155871>  Tat </PROT1_155871> protein is expressed in cells obtained from the central nervous system of patients affected by encephalitic AIDS ( 14 ) CITATION . It has also been shown that , at concentrations of 0.1 & # 150 ; 10 nM , <PROT1_155871>  Tat </PROT1_155871> protein activates various signal transduction pathways in neurons , including phosphatidylinositol 3 kinase ( PI - 3K ) ( 15 CITATION , 16 ) CITATION , <PROT2_5594>  ERK </PROT2_5594> / MAPK ( 17 ) TARGET_CITATION , and the cyclic adenosine monophosphate ( cAMP ) - dependent protein kinase A ( PKA ) pathway ( 18 ) CITATION . ||9394803_155871_5290==>Moreover , the <PROT2_5290>  PI3K </PROT2_5290> / AKT pathway was found to be activated by <PROT1_155871>  Tat </PROT1_155871> in T - lymphoblastoid Jurkat cells ( TARGET_CITATION ) . ||9394803_155871_5290==>Interestingly , two human immunodeficiency virus type 1 ( HIV - 1 ) proteins , <PROT1_155871>  Tat </PROT1_155871> ( TARGET_CITATION ) and Nef ( CITATION ) , both activate the <PROT2_5290>  PI3K </PROT2_5290> - AKT pathway , thus providing antiapoptotic signals . ||9560267_155807_5970==>Alternatively , as shown by ( TARGET_CITATION ) , <PROT1_155807>  Vpr </PROT1_155807> may modulate the transcriptional coactivator p300 , which promotes cooperative interactions between the <PROT2_5970>  RelA </PROT2_5970> subunit of NF - kB and cyclin B1.Cdc2 . ||9621077_155871_3791==>The evidence that vitronectin facilitates the phosphorylation of <PROT2_3791>  VEGFR </PROT2_3791> - 2 prompted us to investigate whether the activation of endothelial cells by VEGF - A , as well as by HIV - 1 - <PROT1_155871>  Tat </PROT1_155871> , another ligand of <PROT2_3791>  VEGFR </PROT2_3791> - 2 which stimulates migration and proliferation of endothelial and Kaposi 's sarcoma cells ( CITATION ; TARGET_CITATION ) , was enhanced by specific substrates . ||9621077_155871_3791==>The HIV transcription factor , <PROT1_155871>  tat </PROT1_155871> , has also been reported to bind to <PROT2_3791>  KDR </PROT2_3791> and stimulate receptor autophosphorylation ( TARGET_CITATION ) . ||9621077_155871_3791==>Thus , although <PROT1_155871>  Tat </PROT1_155871> binds the VEGF receptor Flk - 1 / <PROT2_3791>  KDR </PROT2_3791> CITATION , TARGET_CITATION , this does not lead to cell growth . ||9621077_155871_3791==>HIV - 1 <PROT1_155871>  TAT </PROT1_155871> , via its basic domain , can also bind to and activate the Flk - 1 / <PROT2_3791>  KDR </PROT2_3791> receptor in KS cells ( CITATION , TARGET_CITATION ) . ||9621077_155871_3791==><PROT1_155871>  Tat </PROT1_155871> has been shown to bind to and activate <PROT2_3791>  VEGFR </PROT2_3791> - 2 CITATION TARGET_CITATION , to stimulate KS spindle cell growth CITATION , and to induce neovascularization in vivo CITATION CITATION and in transgenic mice CITATION . <PROT2_3791>  VEGFR </PROT2_3791> - 3 is also increased in KS CITATION , and its ligand , VEGF - C , stimulates the proliferation of KS cells in vitro CITATION . It thus seems probable that an autocrine VEGF / <PROT2_3791>  VEGFR </PROT2_3791> activation loop plays a part in the development of AIDS - linked KS . ||9621077_155871_3791==>Additionally , <PROT1_155871>  Tat </PROT1_155871> binds to and activates the tyrosine kinase receptors encoded by the <PROT2_3791>  KDR </PROT2_3791> and Flt - 1 genes in EC and Kaposi 's sarcoma cells ( CITATION , TARGET_CITATION ) and monocytes ( CITATION ) , respectively . ||9621077_155871_3791==>It has been reported that soluble <PROT1_155871>  Tat </PROT1_155871> induces the activation of vascular endothelium and of Kaposi 's sarcoma cells through the engagement of <PROT2_3791>  VEGFR </PROT2_3791> - 2 ( CITATION , TARGET_CITATION ) and the integrin system ( CITATION , CITATION , CITATION ) . ||9621077_155871_3791==>Because <PROT1_155871>  Tat </PROT1_155871> signals inside the cells through the tyrosine kinase <PROT2_3791>  VEGFR </PROT2_3791> - 2 ( CITATION , TARGET_CITATION , CITATION ) , we investigated the tyrosine phosphorylation of <PROT2_3791>  VEGFR </PROT2_3791> - 2 . ||9621077_155871_3791==>The dramatic reduction in ( I125 ) albumin leakage elicited by an anti - <PROT2_3791>  VEGFR </PROT2_3791> - 2 Ab in both <PROT1_155871>  Tat </PROT1_155871> - MBP - and VEGF - A - treated skin indicates that both molecules activated in vivo <PROT2_3791>  VEGFR </PROT2_3791> - 2 , as also reported in vitro on EC and Kaposi & # 146 ; s sarcoma cells ( TARGET_CITATION , CITATION ) . ||9621077_155871_3791==>Previous studies have demonstrated that HIV - 1 <PROT1_155871>  Tat </PROT1_155871> can bind to and activate specific surface receptors including the Flk - 1 / <PROT2_3791>  KDR </PROT2_3791> receptor for vascular endothelial growth factor ( VEGF ) , 3 and the { alpha } 5 { beta } 1 , { alpha } V { beta } 3 , and { alpha } V { beta } 5 integrins ( CITATION , CITATION , TARGET_CITATION , CITATION ) . ||9621077_155871_3791==>HIV - 1 <PROT1_155871>  Tat </PROT1_155871> activation of Flk - 1 / <PROT2_3791>  KDR </PROT2_3791> ( CITATION ) , FLT - 1 ( CITATION , TARGET_CITATION ) , and { alpha } 5 { beta } 1 and { alpha } V { beta } 3 integrins ( CITATION , CITATION , CITATION ) may cause cells to be `` confused '' by the multiplicity of pathways simultaneously activated , whereas these phenomena do not normally occur in the presence of physiological ligands . ||9621077_155871_3791==>Additionally , <PROT1_155871>  Tat </PROT1_155871> binds to and activates the tyrosine kinase receptor encoded by <PROT2_3791>  KDR </PROT2_3791> ( vascular endothelial growth factor ( VEGF ) receptor ( R ) 2 ) in EC and Kaposi 's cells ( CITATION , CITATION , TARGET_CITATION , CITATION , CITATION and CITATION ) . ||9621077_155871_3791==>KS cells express both <PROT2_3791>  VEGFR2 </PROT2_3791> ( TARGET_CITATION , CITATION , CITATION and CITATION ) and small alpha , Greek5small beta , Greek1 and small alpha , Greekvsmall beta , Greek3 integrins ( CITATION , CITATION and CITATION ) that are the receptors for <PROT1_155871>  Tat </PROT1_155871> mediating EC activation . ||9621077_155871_3791==><PROT1_155871>  Tat </PROT1_155871> ligation of these specific surface molecules activates several cellular protein kinases TARGET_CITATION , CITATION , including Flk - 1 / <PROT2_3791>  KDR </PROT2_3791> , Flt - 1 , and MAP kinase . ||9621077_155871_3791==>The RGD and basic domains of <PROT1_155871>  Tat </PROT1_155871> stimulate and modulate the VEGF receptor Flk - 1 / <PROT2_3791>  KDR </PROT2_3791> and components of the focal adhesion kinase in Kaposi 's sarcoma cells ( TARGET_CITATION , CITATION ) . ||9621077_155871_3791==>HIV - <PROT1_155871>  Tat </PROT1_155871> can also activate the VEGF receptor Flk - 1 / <PROT2_3791>  KDR </PROT2_3791> , acting as a pro - angiogenic factor CITATION , TARGET_CITATION . ||9621077_155871_3791==>However , because the proangiogenic factor VEGF - A CITATION and presumably the HIV - <PROT1_155871>  Tat </PROT1_155871> protein which activates the VEGF - Areceptor Flk - 1 / <PROT2_3791>  KDR </PROT2_3791> CITATION , TARGET_CITATION can induce SDF - 1 expression on endothelial cells , the capillary vasculature of the lung and the gastrointestinal tract could also become SDF - 1 positive , perhaps under hypoxic conditions . 
binds====10096020_10524_155871==><PROT1_10524>  Tip60 </PROT1_10524> was discovered as an HIV - 1 <PROT2_155871>  Tat </PROT2_155871> interacting protein ( CITATION ) and is capable of acetylating several lysine residues in the amino - terminal tails of core histones H2A , H3 , and H4 ( TARGET_CITATION ) . ||10096576_155030_5478==>Supporting this hypothesis , several studies suggest that affinities of <PROT2_5478>  CypA </PROT2_5478> for <PROT1_155030>  Gag </PROT1_155030> and for CA are strikingly different ( TARGET_CITATION , CITATION , CITATION ) . ||10096576_155030_5478==><PROT2_5478>  CypA </PROT2_5478> binds the <PROT1_155030>  Gag </PROT1_155030> polyprotein more strongly than it binds mature CA ( TARGET_CITATION , CITATION ) . ||10329126_1025_155871==>The quaternary complex between <PROT1_1025>  CDK9 </PROT1_1025> , CycT1 , <PROT2_155871>  Tat </PROT2_155871> , and TAR RNA induces conformational changes in the enzyme that result in the activation of the <PROT1_1025>  CDK9 </PROT1_1025> kinase ( CITATION , CITATION , CITATION , CITATION , CITATION , TARGET_CITATION ) and , subsequently , the release of TAR ( CITATION ) . ||10329126_1025_155871==>Formation of the quaternary complex between <PROT1_1025>  CDK9 </PROT1_1025> , CycT1 , <PROT2_155871>  Tat </PROT2_155871> , and TAR RNA induces conformational changes in the enzyme complex that result in the constitutive activation of the <PROT1_1025>  CDK9 </PROT1_1025> kinase ( CITATION , CITATION , CITATION , CITATION , CITATION , TARGET_CITATION ) . ||10329126_1025_155871==>The formation of a quaternary complex among <PROT1_1025>  CDK9 </PROT1_1025> , cyclin T1 , <PROT2_155871>  Tat </PROT2_155871> , and TAR RNA determines the recruitment of human P - TEFb to the transcription elongation complex and the efficient synthesis of long productive viral transcripts ( CITATION , CITATION , CITATION , TARGET_CITATION , CITATION , CITATION ) . ||10329126_1025_155871==><PROT2_155871>  Tat </PROT2_155871> is brought to the HIV promoter by interacting with the TAR RNA hairpin located at the 5 ' end of the viral mRNA transcripts and forms a ternary complex with cyclin T1 , which recruits the <PROT1_1025>  Cdk9 </PROT1_1025> kinase ( CITATION , CITATION , CITATION , CITATION , CITATION , TARGET_CITATION , CITATION ) . ||10329126_155871_904==>For example , HIV - 1 <PROT1_155871>  Tat </PROT1_155871> is unable to bind cooperatively with murine <PROT2_904>  CycT1 </PROT2_904> to TAR RNA ( CITATION , CITATION , CITATION , CITATION , CITATION , TARGET_CITATION ) , and TAR RNA - binding and <PROT1_155871>  Tat </PROT1_155871> transactivation could be rescued by expression of human <PROT2_904>  CycT1 </PROT2_904> or a murine <PROT2_904>  CycT1 </PROT2_904> protein containing a point mutation ( Y261C ) in the <PROT1_155871>  Tat </PROT1_155871> - TAR recognition motif ( CITATION , CITATION ) . ||10329126_155871_904==>It later became clear that the mechanistic explanation for the defect was the inability of the murine form of the essential <PROT1_155871>  Tat </PROT1_155871> cofactor , <PROT2_904>  CycT1 </PROT2_904> , to support efficient interaction with the TAR element when bound to <PROT1_155871>  Tat </PROT1_155871> ( CITATION , CITATION , CITATION , TARGET_CITATION , CITATION ) . ||10329126_155871_904==>Alternatively , substitution of a single amino acid in the murine <PROT2_904>  CycT1 </PROT2_904> protein , tyrosine 261 , with its human <PROT2_904>  CycT1 </PROT2_904> counterpart , cysteine , results in a <PROT2_904>  CycT1 </PROT2_904> protein that can be efficiently recruited to TAR by <PROT1_155871>  Tat </PROT1_155871> proteins and , hence , support transactivation ( CITATION , CITATION , CITATION , CITATION , TARGET_CITATION ) . ||10329126_155871_904==><PROT1_155871>  Tat </PROT1_155871> transactivation is abolished in mouse cells because HIV - 1 <PROT1_155871>  Tat </PROT1_155871> is unable to bind cooperatively with murine <PROT2_904>  CycT1 </PROT2_904> to TAR RNA structure ( CITATION - TARGET_CITATION ) . ||10329126_155871_904==>The formation of the tripartite complex between <PROT1_155871>  Tat </PROT1_155871> , <PROT2_904>  CycT1 </PROT2_904> , and TAR depends on the 5 ' bulge and central loop in TAR ( CITATION , CITATION , CITATION , CITATION , CITATION - TARGET_CITATION , CITATION ) . ||10329126_155871_904==>Finally , the species - specific restriction of HIV - 1 <PROT1_155871>  Tat </PROT1_155871> transactivation has been closely linked to the <PROT2_904>  CycT1 </PROT2_904> subunit of P - TEFb ( CITATION - TARGET_CITATION ) . ||10329126_155871_904==>Mouse <PROT2_904>  CycT1 </PROT2_904> differs from its human homologue at several amino acids , and the change from tyrosine to cysteine at position 261 prevents it from interacting with <PROT1_155871>  Tat </PROT1_155871> ( CITATION , CITATION , TARGET_CITATION ) . ||10329126_155871_904==>Interestingly , the substitution of a single amino residue ( tyrosine - 261 ) in mouse <PROT2_904>  CycT1 </PROT2_904> compared to its human homologue was previously identified as the major determinant restricting <PROT1_155871>  Tat </PROT1_155871> - mediated HIV - 1 LTR transactivation in NIH 3T3 cells ( CITATION , CITATION , TARGET_CITATION , CITATION ) . ||10329126_155871_904==>The change of amino residue 261 from cysteine to tyrosine in <PROT2_904>  CycT1 </PROT2_904> had previously been shown to be the major determinant restricting <PROT1_155871>  Tat </PROT1_155871> - mediated HIV - 1 LTR transactivation in NIH 3T3 cells ( CITATION , CITATION , TARGET_CITATION , CITATION ) . ||10329126_155871_904==>Human <PROT2_904>  cycT1 </PROT2_904> markedly stimulates <PROT1_155871>  Tat </PROT1_155871> activation , while cycT2a and T2b fail to form a complex with <PROT1_155871>  Tat </PROT1_155871> bound to the transactivation response RNA element ( TAR ) ( TARGET_CITATION ; CITATION ) . ||10329126_155871_904==>Human <PROT2_904>  cycT1 </PROT2_904> stimulates <PROT1_155871>  Tat </PROT1_155871> activation , while cycT2a and T2b fail to form a complex with <PROT1_155871>  Tat </PROT1_155871> bound to the transactivation response RNA element ( TAR ) ( TARGET_CITATION ; CITATION ) . ||10329126_155871_904==>The quaternary complex between CDK9 , <PROT2_904>  CycT1 </PROT2_904> , <PROT1_155871>  Tat </PROT1_155871> , and TAR RNA induces conformational changes in the enzyme that result in the activation of the CDK9 kinase ( CITATION , CITATION , CITATION , CITATION , CITATION , TARGET_CITATION ) and , subsequently , the release of TAR ( CITATION ) . ||10329126_155871_904==>Formation of the quaternary complex between CDK9 , <PROT2_904>  CycT1 </PROT2_904> , <PROT1_155871>  Tat </PROT1_155871> , and TAR RNA induces conformational changes in the enzyme complex that result in the constitutive activation of the CDK9 kinase ( CITATION , CITATION , CITATION , CITATION , CITATION , TARGET_CITATION ) . ||10329126_155871_904==>Although the C - terminal region of <PROT2_904>  CycT1 </PROT2_904> might play a role in TAR binding and binds the C - terminal domain , the N - terminal 272 amino acids of <PROT2_904>  CycT1 </PROT2_904> are sufficient for <PROT1_155871>  Tat </PROT1_155871> transactivation in vitro and in vivo ( CITATION , CITATION , CITATION - CITATION , CITATION , TARGET_CITATION , CITATION ; k. Fujinaga , d. Irwin , m. Geyer , r. Taube , and b. m. Peterlin , submitted for publication ) . ||10329126_155871_904==>Since the cysteine at position 261 is changed to tyrosine in the murine <PROT2_904>  CycT1 </PROT2_904> ( mCycT1 ) , mCycT1 can not support <PROT1_155871>  Tat </PROT1_155871> transactivation ( CITATION , CITATION , CITATION , CITATION , TARGET_CITATION ) . ||10329126_155871_904==>This intracellular restriction could be partially overcome by the introduction of human cyclin T1 ( <PROT2_904>  CycT1 </PROT2_904> ) ( CITATION , CITATION , CITATION , TARGET_CITATION , CITATION ) , indicating that human <PROT2_904>  CycT1 </PROT2_904> is essential for <PROT1_155871>  Tat </PROT1_155871> - mediated transcription . ||10329126_155871_904==>Human and murine forms of <PROT2_904>  CycT1 </PROT2_904> are 90 % identical at the amino acid level ; a single amino acid change from cysteine to tyrosine at position 261 of murine <PROT2_904>  CycT1 </PROT2_904> prevents it from interacting with <PROT1_155871>  Tat </PROT1_155871> ( CITATION , CITATION , TARGET_CITATION ) . ||10329126_155871_904==>A single amino acid change at residue 261 from cysteine to tyrosine in murine <PROT2_904>  CycT1 </PROT2_904> has been shown to be the major determinant in restriction of <PROT1_155871>  Tat </PROT1_155871> - mediated HIV - 1 LTR trans - activation in NIH 3T3 cells ( CITATION , CITATION , CITATION , TARGET_CITATION , CITATION ) . ||10497173_155871_6383==>We have recently observed that <PROT1_155871>  Tat </PROT1_155871> internalization requires binding of the protein to cell surface HSPGs , since the uptake process does not occur in cells selectively impaired in <PROT2_6383>  HSPG </PROT2_6383> biosynthesis and can be abolished by cell treatment with heparinase III or by competition with soluble , extracellular heparin ( TARGET_CITATION , CITATION ) . ||10661406_1025_155871==>The cyclin domain is responsible for binding <PROT1_1025>  CDK9 </PROT1_1025> and various other proteins , including NF - { kappa } B ( CITATION ) CIITA ( TARGET_CITATION ) , and GRIP1 ( CITATION ) ; the TRM allows the cooperative binding of <PROT2_155871>  Tat </PROT2_155871> and TAR to cyclin T1 ( CITATION ) ; the His - rich region binds the CTD of RNA polymerase II ( CITATION ) as well as granulin ( CITATION ) ; and the PEST domain is required for the interaction with SCFSKP2 ( CITATION ) . ||10661406_1025_155871==>Since the isolation of cyclin T1 as a <PROT1_1025>  CDK9 </PROT1_1025> partner and <PROT2_155871>  Tat </PROT2_155871> - interacting protein , three other cellular proteins have been identified that bind directly to the cyclin box ( amino acids 1 to 254 ) of cyclin T1 , the major histocompatibility complex class II transactivator CIITA , the NF - { kappa } B RelA / p65 subunit , and the glucocorticoid receptor interacting polypeptide 1 GRIP - 1 ( CITATION , TARGET_CITATION , CITATION ) . ||10931842_155807_904==>The association of <PROT1_155807>  Vpr </PROT1_155807> with Tat and <PROT2_904>  CycT1 </PROT2_904> also stimulates LTR - driven transcription ( TARGET_CITATION ) . ||11024024_155871_6383==><PROT2_6383>  HSPG </PROT2_6383> are also involved in the uptake and internalization of small basic molecules such as polyamines ( CITATION ) and basic peptides such as fibroblast growth factor ( CITATION ) and human immunodeficiency virus - 1 <PROT1_155871>  Tat </PROT1_155871> ( TARGET_CITATION ) as well as of virus particles ( CITATION , CITATION ) . ||11024024_155871_6383==>More recently a role for cell - surface heparan sulfate proteoglycans ( <PROT2_6383>  HSPG </PROT2_6383> ) in cellular uptake of a recombinant GST - <PROT1_155871>  Tat </PROT1_155871> - GFP fusion protein was shown by the same group ( TARGET_CITATION ) . ||11024024_155871_6383==>Tyagi et al. ( TARGET_CITATION ) suggested a requirement of <PROT2_6383>  HSPG </PROT2_6383> for cellular uptake of a GST - <PROT1_155871>  Tat </PROT1_155871> - GFP fusion protein . ||11024024_155871_6383==>We have demonstrated the ability of a 14 - amino acid peptide derived from HIV - <PROT1_155871>  Tat </PROT1_155871> to efficiently deliver DNA , HS , and DS into mammalian cells via electrostatic binding and that both CS / DS and <PROT2_6383>  HSPG </PROT2_6383> are involved in peptide - polyanion complex uptake , as opposed to uptake of full - length HIV - <PROT1_155871>  Tat </PROT1_155871> that specifically required <PROT2_6383>  HSPG </PROT2_6383> ( TARGET_CITATION ) . ||11024024_155871_6383==>We have recently observed that <PROT1_155871>  Tat </PROT1_155871> internalization requires binding of the protein to cell surface HSPGs , since the uptake process does not occur in cells selectively impaired in <PROT2_6383>  HSPG </PROT2_6383> biosynthesis and can be abolished by cell treatment with heparinase III or by competition with soluble , extracellular heparin ( CITATION , TARGET_CITATION ) . ||11027346_155871_7852==>Such factors may include the relatively low prevalence of X4 strains in infected populations ; the differential distribution of CCR5 + versus <PROT2_7852>  CXCR4 </PROT2_7852> + target cells in mucosal tissue CITATION ; and , apropos of the subject of this review , a second HIV - encoded chemokine mimic , the <PROT1_155871>  Tat </PROT1_155871> protein CITATION , TARGET_CITATION . ||11027346_155871_7852==>It acts as a chemotactic agonist for neutrophils , basophils ( via CCR3 ) , mast cells ( via CCR3 ) and monocytes ( via CCR2 ) but as an antagonist at <PROT2_7852>  CXCR4 </PROT2_7852> ; importantly <PROT1_155871>  Tat </PROT1_155871> has no activity at CCR5 TARGET_CITATION . ||11027346_155871_7852==><PROT1_155871>  Tat </PROT1_155871> binds and activates vascular endothelial growth factor receptors 1 and 2 ( VEGFR - 1 / Flk - 1 and VEGFR - 2 / Flt - 1 ) in endothelial and other cell types ( CITATION , CITATION and CITATION ) ; interacts with small beta , Greek - chemokine receptors CCR2 and CCR3 and acts as a potent chemoattractant for various leukocytes ( CITATION , CITATION , CITATION and CITATION ) ; binds chemokine receptor <PROT2_7852>  CXCR4 </PROT2_7852> and competes with X4 - HIV - 1 virus infection on T - cells ( CITATION and TARGET_CITATION ) ; and induces cell adhesion through interaction of its RGD domain ( located in its second exon ) with integrin receptors small alpha , Greek5small beta , Greek1 and small alpha , Greekvsmall beta , Greek3 ( CITATION , CITATION and CITATION ) . ||11027346_155871_7852==>Finally , we tested whether the observed pathway of extracellular <PROT1_155871>  Tat </PROT1_155871> internalization also holds true for CD4 + T - cells expressing the <PROT2_7852>  CXCR4 </PROT2_7852> chemokine receptor , which besides acting as a co - receptor for HIV - 1 infection , has also been shown to be a biologically relevant receptor for extracellular <PROT1_155871>  Tat </PROT1_155871> ( TARGET_CITATION , CITATION ) . ||11027346_155871_7852==>In this respect , it is of interest to note that the internalization process in CD4 + T - lymphocytes expressing <PROT2_7852>  CXCR4 </PROT2_7852> , a chemokine receptor that specifically binds extracellular <PROT1_155871>  Tat </PROT1_155871> ( TARGET_CITATION , CITATION ) and mainly resides outside of lipid rafts ( CITATION & # 150 ; CITATION ) , is also severely inhibited by cholesterol depletion , indistinguishable from <PROT2_7852>  CXCR4 </PROT2_7852> - negative cells . ||11027346_155871_7852==><PROT1_155871>  Tat </PROT1_155871> is secreted from virus - infected cells and has been shown to interact extracellularly with the chemokine receptor <PROT2_7852>  CXCR4 </PROT2_7852> ( CITATION and TARGET_CITATION ) . ||11027346_155871_7852==>Provocatively , we and others have recently documented that extracellular soluble full - length <PROT1_155871>  Tat </PROT1_155871> protein binds cell surface <PROT2_7852>  CXCR4 </PROT2_7852> and blocks infection by T - tropic - HIV - 1 ( CITATION and TARGET_CITATION ) . ||11027346_155871_7852==>In the course of studying how <PROT1_155871>  Tat </PROT1_155871> interferes with <PROT2_7852>  CXCR4 </PROT2_7852> - using HIV - 1 subtypes and in investigating the pro - apoptotic and anti - angiogenic properties of linear peptides derived from HIV - 1 - <PROT1_155871>  Tat </PROT1_155871> ( CITATION ) , we were intrigued by the observation that mutations in its cysteine - rich domain ( C25A , C27A ) abolished the anti - HIV effect of <PROT1_155871>  Tat </PROT1_155871> ( TARGET_CITATION ) . ||11027346_155871_7852==>These results are in agreement with the finding of ( TARGET_CITATION ) that <PROT1_155871>  Tat </PROT1_155871> protein behaves as specific <PROT2_7852>  CXCR4 </PROT2_7852> antagonist which inhibits the entry and replication of X4 but not R5 viruses in PBMC . ||11027346_155871_7852==>HIV - 1 <PROT1_155871>  Tat </PROT1_155871> has been reported to function as an antagonist for <PROT2_7852>  CXCR4 </PROT2_7852> TARGET_CITATION . ||11027346_155871_7852==><PROT1_155871>  Tat </PROT1_155871> can bind to several receptors at the plasma membrane , such as CD26 ( Gutheil et al. , 1994 CITATION ) , <PROT2_7852>  CXCR4 </PROT2_7852> ( Xiao et al. , 2000 TARGET_CITATION ) , heparan sulfate proteoglycans ( Tyagi et al. , 2001 CITATION ) , and the low - density lipoprotein receptor & # 150 ; related protein ( LRP ) ( Liu et al. , 2000 CITATION ) . ||11027346_155871_7852==>TARGET_CITATION report that the HIV - 1 <PROT1_155871>  Tat </PROT1_155871> protein , which is secreted from virus - infected cells , is a <PROT2_7852>  CXCR4 </PROT2_7852> - specific antagonist that can selectively inhibit the entry and replication of SI , but not NSI , forms in peripheral blood mononuclear cells , thereby restricting the target cell substrate preferentially for the SI form . ||11087358_155807_5886==>For example , the human immunodeficiency virus <PROT1_155807>  vpr </PROT1_155807> protein can bind to the second uba domain of <PROT2_5886>  hHR23A </PROT2_5886> ( Withers - Ward et al. , 1997 CITATION ) , but not to a number of other uba domains ( Withers - Ward et al. , 2000 TARGET_CITATION ) . ||11250896_155030_5478==>Cyclophilin A ( <PROT2_5478>  CyPA </PROT2_5478> ; Cpr1p ) binds to the human immunodeficiency virus type 1 ( HIV - 1 ) <PROT1_155030>  Gag </PROT1_155030> protein ( CITATION ) and is required for wild - type HIV - 1 replication kinetics ( TARGET_CITATION ) . ||11250896_155030_5478==>This mutant <PROT2_5478>  CypA </PROT2_5478> contains a lesion in the catalytic site ( H126A ) that abolishes both isomerase activity and the capacity to bind to the HIV - 1 <PROT1_155030>  Gag </PROT1_155030> ( TARGET_CITATION , CITATION ) or to CsA ( CITATION ) . ||11250896_155030_5478==>Cyclophilin A ( <PROT2_5478>  CyPA </PROT2_5478> ) is incorporated into HIV - 1 virions via interaction with the CA domain of the <PROT1_155030>  Gag </PROT1_155030> polyprotein and is required for wild - type viral replication kinetics ( TARGET_CITATION ) . ||11250896_155030_5478==>An interaction between the HIV - 1 <PROT1_155030>  Gag </PROT1_155030> - encoded <PROT1_155030>  capsid </PROT1_155030> ( CA ) protein and the prolyl isomerase cyclophilin A ( <PROT2_5478>  CypA </PROT2_5478> ) is required for efficient HIV - 1 replication ( TARGET_CITATION ) . ||11250896_155030_5478==>Consistent with previous reports studying the effects of CsA treatment ( CITATION , CITATION ) , <PROT1_155030>  Gag </PROT1_155030> mutation ( CITATION ) , or <PROT2_5478>  CypA </PROT2_5478> gene targeting ( TARGET_CITATION ) on HIV - 1 replication , <PROT2_5478>  CypA </PROT2_5478> activity was not required for efficient expression and processing of HIV - 1 <PROT1_155030>  Gag </PROT1_155030> polyproteins ( fig. 3A ) . ||11250896_155030_5478==>Samples were normalized for CA protein , because it has been shown that inactivation of <PROT2_5478>  CypA </PROT2_5478> does not affect the content and processing of <PROT1_155030>  Gag </PROT1_155030> in HIV - 1 virions ( TARGET_CITATION ) . ||11250896_155030_5478==><PROT2_5478>  CypA </PROT2_5478> binds to the human immunodeficiency virus type 1 <PROT1_155030>  Gag </PROT1_155030> protein and is required for wild - type human immunodeficiency virus type 1 replication kinetics ( TARGET_CITATION ) . ||11250896_155030_5478==>Aside from minimal effects on the kinetics of <PROT1_155030>  gag </PROT1_155030> processing or virion release ( CITATION , CITATION ) , disruption of <PROT2_5478>  CypA </PROT2_5478> incorporation into virions has no effect on biochemical or ultrastructural characteristics of HIV - 1 virions , including endogenous reverse transcription ( CITATION , TARGET_CITATION , CITATION , CITATION , CITATION , CITATION ) . ||11427703_155030_7251==>In a separate study , VerPlank et al. ( TARGET_CITATION ) used a yeast two - hybrid screen of a B cell library with HIV - 1 <PROT1_155030>  Gag </PROT1_155030> as bait and isolated the protein <PROT2_7251>  Tsg101 </PROT2_7251> , which interacts with the PTAPP L domain sequence of HIV - 1 p6 . ||11427703_155030_7251==>In contrast , VerPlank et al. ( TARGET_CITATION ) reported that mutating the Ub - acceptor sites in p6 had no effect on <PROT1_155030>  Gag </PROT1_155030> / <PROT2_7251>  TSG101 </PROT2_7251> binding in yeast two - hybrid assays . ||11427703_155030_7251==>Although the physiological ligand for p6 has not been definitively identified , a variety of observations suggest that retroviral L domains function by interacting with the host ubiquitination machinery ( reviewed in reference CITATION ) : ( i ) The L domain - containing proteins of MuLV ( p12 ) and HIV ( p6 ) are ubiquitinated ( CITATION ) , ( ii ) depletion of free ubiquitin in virus - producing cells with proteasome inhibitors impairs retrovirus budding ( CITATION , CITATION ) , ( iii ) the presence of L domains in HIV - 1 minimal <PROT1_155030>  Gag </PROT1_155030> constructs induces ubiquitination of the minimal <PROT1_155030>  Gag </PROT1_155030> proteins ( CITATION ) , ( iv ) the ubiquitin ligase Nedd4 interacts with the RSV L domain ( CITATION ) , and ( v ) the cellular protein <PROT2_7251>  TSG101 </PROT2_7251> , which contains at its N terminus a ubiquitin - conjugating enzyme - like sequence , interacts with HIV - 1 <PROT1_155030>  Gag </PROT1_155030> in a p6 - dependent fashion ( TARGET_CITATION ) . ||11427703_155030_7251==>Comparison of the cDNA sequences with the GenBank database revealed that one of the clones was human EF1 { alpha } and another was human <PROT2_7251>  Tsg101 </PROT2_7251> , an inactive homologue of ubiquitin ligase E2 , both of which have been reported to interact with HIV - 1 <PROT1_155030>  Gag </PROT1_155030> ( CITATION , CITATION , TARGET_CITATION ) . ||11427703_155030_7251==><PROT2_7251>  Tsg101 </PROT2_7251> interacted specifically with HIV - 2 <PROT1_155030>  Gag </PROT1_155030> and also with HIV - 1 <PROT1_155030>  Gag </PROT1_155030> , as previously reported ( CITATION , TARGET_CITATION ) . ||11427703_155030_7251==>While we were carrying out this work , there have been reports of an interaction between HIV - 1 <PROT1_155030>  Gag </PROT1_155030> and <PROT2_7251>  Tsg101 </PROT2_7251> ( CITATION , CITATION , TARGET_CITATION ) . ||11427703_155030_7251==>In agreement with studies on the interaction of <PROT2_7251>  Tsg101 </PROT2_7251> with HIV - 1 <PROT1_155030>  Gag </PROT1_155030> ( TARGET_CITATION ) , we have demonstrated that the N - terminal Ubc - conjugation homology domain of <PROT2_7251>  Tsg101 </PROT2_7251> is required for interaction with HIV - 2 <PROT1_155030>  Gag </PROT1_155030> and that overexpression of this portion of <PROT2_7251>  Tsg101 </PROT2_7251> ( amino acid residues 1 to 167 ) inhibits the release of HIV - 2 particles . ||11427703_155030_7251==>Via interaction with the PTAP motif in the p6 domain of <PROT1_155030>  Gag </PROT1_155030> , the ubiquitin - conjugating enzyme homologue <PROT2_7251>  Tsg101 </PROT2_7251> is targeted to the site of virion budding , where it is required for fission of the nascent virion membrane from the host cell membrane ( CITATION , CITATION , TARGET_CITATION ) . ||11427703_155030_7251==>Recently , the product of the tumor suppressor gene 101 ( <PROT2_7251>  TSG101 </PROT2_7251> ) was shown to bind the PTAP motif of p6 <PROT1_155030>  Gag </PROT1_155030> and also to recognize ubiquitin through its ubiquitin enzyme 2 ( UEV ) domain CITATION , TARGET_CITATION . ||11427703_155030_7251==>Finally , ( iv ) the cellular protein <PROT2_7251>  TSG101 </PROT2_7251> , which contains at its N terminus a domain related to Ub conjugating ( E2 ) enzymes , binds <PROT1_155030>  Gag </PROT1_155030> in a p6 - dependent manner ( TARGET_CITATION ) . ||11427703_155030_7251==>We observed that both <PROT2_7251>  TSG101 </PROT2_7251> and HRS contain a tetrapeptide motif ( PTAP in TSG ; PSAP in HRS ) that initially was identified in an HIV <PROT1_155030>  GAG </PROT1_155030> protein late domain that interacts with the UEV domain of <PROT2_7251>  TSG101 </PROT2_7251> ( CITATION , TARGET_CITATION ) . ||11427703_155030_7251==><PROT2_7251>  TSG101 </PROT2_7251> interaction with this motif of <PROT1_155030>  GAG </PROT1_155030> ( CITATION , TARGET_CITATION ) and with a similar motif in the <PROT1_155030>  matrix </PROT1_155030> protein of Ebola virus ( CITATION ) is required for normal viral budding to the cell surface , a process that is topologically equivalent to the removal of mitogenic receptors from the cytoplasm ( CITATION ) . ||11427703_155030_7251==>The budding virus particle is ultimately released from the cell surface in a process that is promoted by an interaction between the late domain in the p6 region of <PROT1_155030>  Gag </PROT1_155030> ( CITATION , CITATION ) and host proteins , most notably the endosomal sorting factor <PROT2_7251>  TSG101 </PROT2_7251> ( tumor susceptibility gene 101 ) ( TARGET_CITATION - CITATION ) . ||11427703_155030_7251==>A ubiquitin binding domain ( designated ubiquitin E2 variant sequence ( UEV ) ) at the NH2 terminus of <PROT2_7251>  Tsg101 </PROT2_7251> binds to the PTAP motif , and the binding is enhanced if the <PROT1_155030>  Gag </PROT1_155030> p6 polypeptide is ubiquitinated ( CITATION ; TARGET_CITATION ; CITATION ) . ||11427703_155030_7251==>The HIV - 1 encoded <PROT1_155030>  Gag </PROT1_155030> protein has been shown to interact with the mammalian orthologue of Vps23 ( <PROT2_7251>  Tsg101 </PROT2_7251> ) and , thereby , recruits ESCRT - I to the plasma membrane where it functions in viral budding ( CITATION ; CITATION ; TARGET_CITATION ) . ||11427703_155030_7251==>This region of Vps27 contains two motifs ( PSDP524 & # 150 ; 527 and PTVP581 & # 150 ; 584 ) that are similar to a peptide sequence within the HIV - 1 <PROT1_155030>  Gag </PROT1_155030> protein ( PTAP ) which is capable of interacting with <PROT2_7251>  Tsg101 </PROT2_7251> ( CITATION ; CITATION ; TARGET_CITATION ) . ||11427703_155030_7251==>The carboxy - terminus of <PROT1_155030>  Gag </PROT1_155030> , p6 , is ubiquitylated CITATION , and it recruits components of multivesicular bodies , such as tumour - susceptibility gene 101 ( <PROT2_7251>  TSG101 </PROT2_7251> ) and vacuolar protein sorting 4 ( VPS4 ) CITATION - TARGET_CITATION , which facilitate the release of progeny virions from the cell . ||11427703_155030_7251==>To determine whether the inhibition of virus release imposed by TSG - 5 ' is dependent upon its interaction with <PROT1_155030>  Gag </PROT1_155030> , we mutated a region of <PROT2_7251>  TSG101 </PROT2_7251> previously shown to be important for <PROT1_155030>  Gag </PROT1_155030> / <PROT2_7251>  TSG101 </PROT2_7251> interaction ( CITATION , CITATION , TARGET_CITATION ) . ||11427703_155030_7251==>There is growing evidence that this process involves the ubiquitin E3 ligase Nedd4 ( CITATION , CITATION , CITATION ) and variant E2 - like protein <PROT2_7251>  TSG101 </PROT2_7251> ( CITATION , CITATION , TARGET_CITATION ) acting through interactions ( CITATION ) with late domain motifs ( CITATION ) in viral <PROT1_155030>  Gag </PROT1_155030> proteins to ligate ubiquitin . ||11427703_155030_7251==>The best - characterized late - domain interaction is that of the PTAP motif in the p6 region of HIV - 1 <PROT1_155030>  Gag </PROT1_155030> with cellular <PROT2_7251>  TSG101 </PROT2_7251> ( CITATION , TARGET_CITATION ) . ||11427703_155030_7251==>Recently , the PTAPP motif , or L domain , of human immunodeficiency virus type 1 ( HIV - 1 ) , which is located in the C - terminal p6 region of the <PROT1_155030>  Gag </PROT1_155030> precursor polyprotein , was found to bind to the protein product of the <PROT2_7251>  tsg101 </PROT2_7251> gene ( CITATION , CITATION , TARGET_CITATION ) . ||11427703_155030_7251==>The N - terminal domain of <PROT2_7251>  Tsg101 </PROT2_7251> also is the minimal binding region required for its interaction with HIV - 1 <PROT1_155030>  Gag </PROT1_155030> ( CITATION , CITATION , TARGET_CITATION ) . ||11427703_155030_7251==>The positive controls confirmed the activities of the constructs : the HIV - 1 <PROT1_155030>  Gag </PROT1_155030> bound <PROT2_7251>  Tsg101 </PROT2_7251> as previously described ( CITATION , CITATION , TARGET_CITATION ) but not with Nedd4 , and MLV <PROT1_155030>  Gag </PROT1_155030> interacted with Nedd4 protein but not with <PROT2_7251>  Tsg101 </PROT2_7251> . ||11427703_155030_7251==>Indeed , many of the virus - encoded proteins have been shown to interact with cellular proteins , e.g. , <PROT1_155030>  Gag </PROT1_155030> and <PROT2_7251>  Tsg101 </PROT2_7251> ( CITATION , CITATION , CITATION , TARGET_CITATION ) , <PROT1_155030>  Gag </PROT1_155030> and cyclophilins ( CITATION ) , integrase and Ini1 ( CITATION ) , Vpr and PP2A ( CITATION ) , Vpr and HHR23A ( CITATION ) , Vpr and UNG ( CITATION ) , Vif and antiviral proteins ( CITATION , CITATION ) , Vif and HP68 ( CITATION ) , and Tat and cyclin T1 ( CITATION , CITATION ) . ||11427703_155030_7251==>In this case , <PROT2_7251>  TSG101 </PROT2_7251> binds the L - domain of the retroviral <PROT1_155030>  gag </PROT1_155030> protein and promotes its monoubiquitination ( CITATION , TARGET_CITATION ) , which is a prerequisite for viral release ( CITATION ) . ||11427703_155030_7251==>In addition , a number of host factors appropriated by the virus ( <PROT2_7251>  Tsg101 </PROT2_7251> , ubiquitin , ERK2 , cyclophilin A ( CypA ) , and topoisomerase I ) interact specifically with elements of the HIV - 1 <PROT1_155030>  Gag </PROT1_155030> polyprotein and contribute to assembly , release , and subsequent postentry events in the viral life cycle ( CITATION , CITATION , CITATION , CITATION , CITATION - CITATION , TARGET_CITATION ) . ||11427703_155030_7251==>Most lentiviruses carry a P ( T / S ) AP motif which is located at the end of <PROT1_155030>  Gag </PROT1_155030> and interacts with <PROT2_7251>  TSG101 </PROT2_7251> ( CITATION , CITATION , CITATION , TARGET_CITATION ) . ||11427703_155030_7251==>The L domain of HIV - 1 <PROT1_155030>  Gag </PROT1_155030> binds to <PROT2_7251>  Tsg101 </PROT2_7251> , which is a component of the ESCRT - 1 endosomal protein sorting complex and is involved in targeting monoubiquitinated proteins to the MVB ( CITATION , CITATION , CITATION , CITATION , TARGET_CITATION ) . ||11427703_155030_7251==>( iii ) <PROT2_7251>  TSG101 </PROT2_7251> can bind p6 in the absence of the <PROT1_155030>  Gag </PROT1_155030> - Ub modification , though ubiquitination may enhance binding ( CITATION , CITATION , TARGET_CITATION ) . ||11427703_155030_7251==>The PTAP motif within the L domain of HIV - 1 <PROT1_155030>  Gag </PROT1_155030> has been shown to interact with <PROT2_7251>  Tsg101 </PROT2_7251> , and this interaction is essential for the final stages of particle budding ( CITATION , TARGET_CITATION ) . ||11427703_155030_7251==><PROT2_7251>  Tsg101 </PROT2_7251> has been identified as a host cell factor that binds the PTAP motif within the p6 region of HIV - 1 <PROT1_155030>  Gag </PROT1_155030> ( CITATION , CITATION , TARGET_CITATION ) . ||11427703_155030_7251==>Recent studies indicated that <PROT1_155030>  Gag </PROT1_155030> interacts directly with <PROT2_7251>  Tsg101 </PROT2_7251> , a ubiquitin enzyme 2 variant family protein that is involved in vesicular sorting pathways in the cell , suggesting that <PROT1_155030>  Gag </PROT1_155030> may utilize components of this pathway to reach the plasma membrane ( CITATION , CITATION , TARGET_CITATION ) . ||11427703_155030_7251==>Functional interactions between <PROT2_7251>  TSG101 </PROT2_7251> and the PTAP motifs present in HIV - 1 <PROT1_155030>  Gag </PROT1_155030> and Ebola virus VP40 have now been well documented ( CITATION , CITATION , CITATION , CITATION , CITATION , CITATION , CITATION , TARGET_CITATION ) . ||11595185_155030_7251==>Recently , TARGET_CITATION reported that <PROT2_7251>  Tsg101 </PROT2_7251> , which functions in vacuolar protein sorting ( Vps ) , binds to the PTAP motif identified as the L domain within HIV <PROT1_155030>  Gag </PROT1_155030> , and is required for HIV - 1 budding . ||11595185_155030_7251==>Depletion of cellular <PROT2_7251>  Tsg101 </PROT2_7251> levels using small interfering RNA causes defects in both the packaging of <PROT1_155030>  Gag </PROT1_155030> and the budding of viral particles TARGET_CITATION . ||11595185_155030_7251==>The affinity of <PROT2_7251>  Tsg101 </PROT2_7251> for the <PROT1_155030>  Gag </PROT1_155030> protein is increased markedly when <PROT1_155030>  Gag </PROT1_155030> is ubiquitylated TARGET_CITATION , and experiments have identified a region , which includes a beta - hairpin in the UBC - like domain of <PROT2_7251>  Tsg101 </PROT2_7251> , that is essential for this interaction CITATION . ||11595185_155030_7251==>Comparison of the cDNA sequences with the GenBank database revealed that one of the clones was human EF1 { alpha } and another was human <PROT2_7251>  Tsg101 </PROT2_7251> , an inactive homologue of ubiquitin ligase E2 , both of which have been reported to interact with HIV - 1 <PROT1_155030>  Gag </PROT1_155030> ( CITATION , TARGET_CITATION , CITATION ) . ||11595185_155030_7251==><PROT2_7251>  Tsg101 </PROT2_7251> interacted specifically with HIV - 2 <PROT1_155030>  Gag </PROT1_155030> and also with HIV - 1 <PROT1_155030>  Gag </PROT1_155030> , as previously reported ( TARGET_CITATION , CITATION ) . ||11595185_155030_7251==>While we were carrying out this work , there have been reports of an interaction between HIV - 1 <PROT1_155030>  Gag </PROT1_155030> and <PROT2_7251>  Tsg101 </PROT2_7251> ( TARGET_CITATION , CITATION , CITATION ) . ||11595185_155030_7251==>Via interaction with the PTAP motif in the p6 domain of <PROT1_155030>  Gag </PROT1_155030> , the ubiquitin - conjugating enzyme homologue <PROT2_7251>  Tsg101 </PROT2_7251> is targeted to the site of virion budding , where it is required for fission of the nascent virion membrane from the host cell membrane ( TARGET_CITATION , CITATION , CITATION ) . ||11595185_155030_7251==>Recently , the product of the tumor suppressor gene 101 ( <PROT2_7251>  TSG101 </PROT2_7251> ) was shown to bind the PTAP motif of p6 <PROT1_155030>  Gag </PROT1_155030> and also to recognize ubiquitin through its ubiquitin enzyme 2 ( UEV ) domain TARGET_CITATION , CITATION . ||11595185_155030_7251==>We observed that both <PROT2_7251>  TSG101 </PROT2_7251> and HRS contain a tetrapeptide motif ( PTAP in TSG ; PSAP in HRS ) that initially was identified in an HIV <PROT1_155030>  GAG </PROT1_155030> protein late domain that interacts with the UEV domain of <PROT2_7251>  TSG101 </PROT2_7251> ( TARGET_CITATION , CITATION ) . ||11595185_155030_7251==><PROT2_7251>  TSG101 </PROT2_7251> interaction with this motif of <PROT1_155030>  GAG </PROT1_155030> ( TARGET_CITATION , CITATION ) and with a similar motif in the <PROT1_155030>  matrix </PROT1_155030> protein of Ebola virus ( CITATION ) is required for normal viral budding to the cell surface , a process that is topologically equivalent to the removal of mitogenic receptors from the cytoplasm ( CITATION ) . ||11595185_155030_7251==>Interactions between the cellular <PROT2_7251>  Tsg101 </PROT2_7251> ( tumor susceptibility gene 101 ) protein and the PTAP motif present in the p6 domain of HIV - 1 <PROT1_155030>  Gag </PROT1_155030> are required for viral budding from the cell membrane ( TARGET_CITATION ) . ||11595185_155030_7251==>Mutating key residues in the p6 late domain ( CITATION - CITATION , CITATION ) or inhibiting the interaction between p6 and <PROT2_7251>  TSG101 </PROT2_7251> ( TARGET_CITATION , CITATION ) also delays <PROT1_155030>  Gag </PROT1_155030> processing and increases levels of the <PROT1_155030>  Gag </PROT1_155030> cleavage intermediates p25 ( CA - SP1 ) and p41 ( MA - CA ) in virions . ||11595185_155030_7251==>As noted in the Introduction , disruption of the interaction between HIV - 1 <PROT1_155030>  Gag </PROT1_155030> and <PROT2_7251>  TSG101 </PROT2_7251> inhibits the conversion of p25 to p24 ( CITATION , CITATION , TARGET_CITATION , CITATION , CITATION ) . ||11595185_155030_7251==>However , clues have come from the recent observation that HIV <PROT1_155030>  Gag </PROT1_155030> interacts with <PROT2_7251>  TSG101 </PROT2_7251> , a member of the ESCRT complex involved in vesicular trafficking within the cell ( TARGET_CITATION ) . ||11595185_155030_7251==>CEM15 / Apobec 3G interferes with the production of infectious virions in the absence of a functional vif allele ( CITATION , CITATION ) ; <PROT2_7251>  TSG101 </PROT2_7251> interacts with the PTAPP motif in <PROT1_155030>  gag </PROT1_155030> p6 , where it facilitates release of virus from cells ( TARGET_CITATION ) . ||11595185_155030_7251==>A ubiquitin binding domain ( designated ubiquitin E2 variant sequence ( UEV ) ) at the NH2 terminus of <PROT2_7251>  Tsg101 </PROT2_7251> binds to the PTAP motif , and the binding is enhanced if the <PROT1_155030>  Gag </PROT1_155030> p6 polypeptide is ubiquitinated ( TARGET_CITATION ; CITATION ; CITATION ) . ||11595185_155030_7251==>The HIV - 1 encoded <PROT1_155030>  Gag </PROT1_155030> protein has been shown to interact with the mammalian orthologue of Vps23 ( <PROT2_7251>  Tsg101 </PROT2_7251> ) and , thereby , recruits ESCRT - I to the plasma membrane where it functions in viral budding ( TARGET_CITATION ; CITATION ; CITATION ) . ||11595185_155030_7251==>This region of Vps27 contains two motifs ( PSDP524 & # 150 ; 527 and PTVP581 & # 150 ; 584 ) that are similar to a peptide sequence within the HIV - 1 <PROT1_155030>  Gag </PROT1_155030> protein ( PTAP ) which is capable of interacting with <PROT2_7251>  Tsg101 </PROT2_7251> ( TARGET_CITATION ; CITATION ; CITATION ) . ||11595185_155030_7251==>Therefore , it is intriguing that sequences involved in Vps27 function and ESCRT - I recruitment are similar to a conserved motif in the HIV - 1 protein <PROT1_155030>  Gag </PROT1_155030> , which has been shown to interact with <PROT2_7251>  Tsg101 </PROT2_7251> ( TARGET_CITATION ) . ||11595185_155030_7251==>Expression of HIV <PROT1_155030>  Gag </PROT1_155030> & # 150 ; GFP fusion proteins in human cell lines recapitulates many aspects of viral assembly and budding ( CITATION ) , including the requirement for <PROT2_7251>  Tsg101 </PROT2_7251> and other components of the MVB pathway ( TARGET_CITATION ) . ||11595185_155030_7251==><PROT1_155030>  Gag </PROT1_155030> carries a PTAP peptide sequence that interacts with the UEV domain of <PROT2_7251>  Tsg101 </PROT2_7251> , and this interaction is enhanced by <PROT1_155030>  Gag </PROT1_155030> monoubiquitination ( TARGET_CITATION ) . ||11595185_155030_7251==>The carboxy - terminus of <PROT1_155030>  Gag </PROT1_155030> , p6 , is ubiquitylated CITATION , and it recruits components of multivesicular bodies , such as tumour - susceptibility gene 101 ( <PROT2_7251>  TSG101 </PROT2_7251> ) and vacuolar protein sorting 4 ( VPS4 ) TARGET_CITATION , which facilitate the release of progeny virions from the cell . ||11595185_155030_7251==>A functional relevance of the <PROT1_155030>  Gag </PROT1_155030> / <PROT2_7251>  TSG101 </PROT2_7251> interaction in virus release is supported by the observation of Garrus et al. ( TARGET_CITATION ) that depletion of <PROT2_7251>  TSG101 </PROT2_7251> using a small interfering RNA approach blocked HIV - 1 budding , and our demonstration that overexpression of the N - terminal , E2 - like domain of <PROT2_7251>  TSG101 </PROT2_7251> ( referred to as TSG - 5 ' ) impaired particle release ( CITATION ) . ||11595185_155030_7251==>There is growing evidence that this process involves the ubiquitin E3 ligase Nedd4 ( CITATION , CITATION , CITATION ) and variant E2 - like protein <PROT2_7251>  TSG101 </PROT2_7251> ( CITATION , TARGET_CITATION , CITATION ) acting through interactions ( CITATION ) with late domain motifs ( CITATION ) in viral <PROT1_155030>  Gag </PROT1_155030> proteins to ligate ubiquitin . ||11595185_155030_7251==>The best - characterized late - domain interaction is that of the PTAP motif in the p6 region of HIV - 1 <PROT1_155030>  Gag </PROT1_155030> with cellular <PROT2_7251>  TSG101 </PROT2_7251> ( TARGET_CITATION , CITATION ) . ||11595185_155030_7251==>HIV - 1 <PROT1_155030>  Gag </PROT1_155030> recruits an ESCRT - 1 complex protein , <PROT2_7251>  TSG101 </PROT2_7251> , via a PTAP motif in the p6 region and possibly through ubiquitin conjugated to <PROT1_155030>  Gag </PROT1_155030> which may interact with a ubiquitin interaction motif in <PROT2_7251>  TSG101 </PROT2_7251> ( TARGET_CITATION ) . ||11595185_155030_7251==>VPS28 normally binds tightly to <PROT2_7251>  TSG101 </PROT2_7251> ( TARGET_CITATION , CITATION ) , suggesting that budded particles arising from expression of the chimeric ld ( - ) <PROT1_155030>  Gag </PROT1_155030> - VPS28 might incorporate <PROT2_7251>  TSG101 </PROT2_7251> . ||11595185_155030_7251==>Recently , the PTAPP motif , or L domain , of human immunodeficiency virus type 1 ( HIV - 1 ) , which is located in the C - terminal p6 region of the <PROT1_155030>  Gag </PROT1_155030> precursor polyprotein , was found to bind to the protein product of the <PROT2_7251>  tsg101 </PROT2_7251> gene ( TARGET_CITATION , CITATION , CITATION ) . ||11595185_155030_7251==>The N - terminal domain of <PROT2_7251>  Tsg101 </PROT2_7251> also is the minimal binding region required for its interaction with HIV - 1 <PROT1_155030>  Gag </PROT1_155030> ( TARGET_CITATION , CITATION , CITATION ) . ||11595185_155030_7251==>Since <PROT2_7251>  TSG101 </PROT2_7251> shows weak binding to ubiquitin alone ( TARGET_CITATION ) , it could be recruited by binding to ubiquitinated <PROT1_155030>  Gag </PROT1_155030> protein . ||11595185_155030_7251==>The EIAV p9 protein harboring the L - domain motif YXXL was shown to bind the AP - 50 subunit of the AP - 2 complex ( CITATION ) .The PTAP motif present in the HIV - 1 and HIV - 2 <PROT1_155030>  Gag </PROT1_155030> polyprotein and VP40 in Ebola virus ( TARGET_CITATION , CITATION , CITATION , CITATION ) binds the E2 ubiquitin enzyme variant ( UEV ) <PROT2_7251>  Tsg101 </PROT2_7251> . ||11595185_155030_7251==>The positive controls confirmed the activities of the constructs : the HIV - 1 <PROT1_155030>  Gag </PROT1_155030> bound <PROT2_7251>  Tsg101 </PROT2_7251> as previously described ( TARGET_CITATION , CITATION , CITATION ) but not with Nedd4 , and MLV <PROT1_155030>  Gag </PROT1_155030> interacted with Nedd4 protein but not with <PROT2_7251>  Tsg101 </PROT2_7251> . ||11595185_155030_7251==>The current model of viral budding involves binding of the 4 - amino - acid <PROT1_155030>  Gag </PROT1_155030> p6 PTAP motif to cellular <PROT2_7251>  Tsg101 </PROT2_7251> protein and subsequent assortment via the cellular vacuolar protein - sorting pathway ( CITATION , TARGET_CITATION , CITATION , CITATION ) . ||11595185_155030_7251==>While it is possible that ubiquitination at alternative HIV - 1 <PROT1_155030>  Gag </PROT1_155030> sites might facilitate <PROT2_7251>  Tsg101 </PROT2_7251> recruitment ( TARGET_CITATION , CITATION ) , the presence of this proven L - domain cofactor at sites of particle assembly appears insufficient to account for the virion morphogenesis activity exhibited by HIV - 1 p6 . ||11595185_155030_7251==>Indeed , many of the virus - encoded proteins have been shown to interact with cellular proteins , e.g. , <PROT1_155030>  Gag </PROT1_155030> and <PROT2_7251>  Tsg101 </PROT2_7251> ( CITATION , TARGET_CITATION , CITATION , CITATION ) , <PROT1_155030>  Gag </PROT1_155030> and cyclophilins ( CITATION ) , integrase and Ini1 ( CITATION ) , Vpr and PP2A ( CITATION ) , Vpr and HHR23A ( CITATION ) , Vpr and UNG ( CITATION ) , Vif and antiviral proteins ( CITATION , CITATION ) , Vif and HP68 ( CITATION ) , and Tat and cyclin T1 ( CITATION , CITATION ) . ||11595185_155030_7251==><PROT2_7251>  tsg101 </PROT2_7251> has been shown to interact with the PTAP L - domain present in HIV - 1 <PROT1_155030>  gag </PROT1_155030> and Ebola virus VP40 by virtue of its N - terminal ubiquitin enzyme 2 variant domain ( TARGET_CITATION , CITATION ) . ||11595185_155030_7251==>An intriguing area for future research is the interaction of <PROT1_155030>  Gag </PROT1_155030> with components of the vacuolar protein sorting pathway , as recently illustrated by the characterization of <PROT2_7251>  TSG101 </PROT2_7251> as a binding partner for the PTAP domain within p6 ( TARGET_CITATION ) . ||11595185_155030_7251==>As a control we used HIV - <PROT1_155030>  Gag </PROT1_155030> , because the single PTAP motif of this viral protein strongly binds to the UEV of <PROT2_7251>  Tsg101 </PROT2_7251> ( Garrus et al. 2001 TARGET_CITATION ; Martin - Serrano et al. 2001 CITATION ; VerPlank et al. 2001 CITATION ; Demirov et al. 2002 CITATION ; Myers and Allen 2002 CITATION ; Pornillos et al. 2002a CITATION ) . ||11595185_155030_7251==>Unlike EGFR , <PROT1_155030>  Gag </PROT1_155030> contains a PTAP motif , which recruits <PROT2_7251>  Tsg101 </PROT2_7251> to virus budding sites ( Garrus et al. 2001 TARGET_CITATION ; Martin - Serrano et al. 2001 CITATION ; VerPlank et al. 2001 CITATION ; Demirov et al. 2002 CITATION ; Myers and Allen 2002 CITATION ; Pornillos et al. 2002a CITATION ) . ||11595185_155030_7251==>In this case , <PROT2_7251>  TSG101 </PROT2_7251> binds the L - domain of the retroviral <PROT1_155030>  gag </PROT1_155030> protein and promotes its monoubiquitination ( CITATION , CITATION ) , which is a prerequisite for viral release ( TARGET_CITATION ) . ||11595185_155030_7251==>The <PROT2_7251>  Tsg101 </PROT2_7251> UEV domain is also able to recognize a PTAP motif from the late domain p6 protein of HIV - 1 <PROT1_155030>  Gag </PROT1_155030> , and this PTAP binding is necessary for efficient viral budding ( TARGET_CITATION , CITATION ) . ||11595185_155030_7251==>In addition , a number of host factors appropriated by the virus ( <PROT2_7251>  Tsg101 </PROT2_7251> , ubiquitin , ERK2 , cyclophilin A ( CypA ) , and topoisomerase I ) interact specifically with elements of the HIV - 1 <PROT1_155030>  Gag </PROT1_155030> polyprotein and contribute to assembly , release , and subsequent postentry events in the viral life cycle ( CITATION , CITATION , TARGET_CITATION , CITATION , CITATION - CITATION , CITATION ) . ||11595185_155030_7251==>Interaction of HIV - 1 <PROT1_155030>  Gag </PROT1_155030> with <PROT2_7251>  Tsg101 </PROT2_7251> and other components of the MVB ESCRT complex is required for efficient particle production ( TARGET_CITATION , CITATION ) . ||11595185_155030_7251==>Most lentiviruses carry a P ( T / S ) AP motif which is located at the end of <PROT1_155030>  Gag </PROT1_155030> and interacts with <PROT2_7251>  TSG101 </PROT2_7251> ( TARGET_CITATION , CITATION , CITATION , CITATION ) . ||11595185_155030_7251==>It is of note that although the PTAP motif within the p6 <PROT1_155030>  Gag </PROT1_155030> has recently been shown to recruit the human protein <PROT2_7251>  Tsg101 </PROT2_7251> to facilitate HIV - 1 budding ( TARGET_CITATION , CITATION ) significant amounts of the mature p6 protein were seen in all of the virions , suggesting that none of the SRPE , APP , or PTAPPA inserts located near the PTAP motif blocked viral budding ( fig. 3 ) . ||11595185_155030_7251==>The L domain of HIV - 1 <PROT1_155030>  Gag </PROT1_155030> binds to <PROT2_7251>  Tsg101 </PROT2_7251> , which is a component of the ESCRT - 1 endosomal protein sorting complex and is involved in targeting monoubiquitinated proteins to the MVB ( CITATION , TARGET_CITATION , CITATION , CITATION , CITATION ) . ||11595185_155030_7251==>( iii ) <PROT2_7251>  TSG101 </PROT2_7251> can bind p6 in the absence of the <PROT1_155030>  Gag </PROT1_155030> - Ub modification , though ubiquitination may enhance binding ( TARGET_CITATION , CITATION , CITATION ) . ||11595185_155030_7251==>The PTAP motif within the L domain of HIV - 1 <PROT1_155030>  Gag </PROT1_155030> has been shown to interact with <PROT2_7251>  Tsg101 </PROT2_7251> , and this interaction is essential for the final stages of particle budding ( TARGET_CITATION , CITATION ) . ||11595185_155030_7251==><PROT2_7251>  Tsg101 </PROT2_7251> has been identified as a host cell factor that binds the PTAP motif within the p6 region of HIV - 1 <PROT1_155030>  Gag </PROT1_155030> ( CITATION , TARGET_CITATION , CITATION ) . ||11595185_155030_7251==>Recent studies indicated that <PROT1_155030>  Gag </PROT1_155030> interacts directly with <PROT2_7251>  Tsg101 </PROT2_7251> , a ubiquitin enzyme 2 variant family protein that is involved in vesicular sorting pathways in the cell , suggesting that <PROT1_155030>  Gag </PROT1_155030> may utilize components of this pathway to reach the plasma membrane ( CITATION , TARGET_CITATION , CITATION ) . ||11595185_155030_7251==><PROT2_7251>  TSG101 </PROT2_7251> exerts its effect on the budding of HIV - 1 by an interaction with the late domain of the viral protein <PROT1_155030>  Gag </PROT1_155030> ( TARGET_CITATION ) . ||11595185_155030_7251==>Functional interactions between <PROT2_7251>  TSG101 </PROT2_7251> and the PTAP motifs present in HIV - 1 <PROT1_155030>  Gag </PROT1_155030> and Ebola virus VP40 have now been well documented ( TARGET_CITATION , CITATION , CITATION , CITATION , CITATION , CITATION , CITATION , CITATION ) . ||12009870_155030_5478==>In addition , even though the <PROT1_155030>  Gag </PROT1_155030> proteins of all HIV - 1 and SIVcpz strains tested bind to <PROT2_5478>  CypA </PROT2_5478> CITATION , the replication of some HIV - 1 'O ' group strains is unaffected by its removal CITATION TARGET_CITATION . ||12009870_155030_5478==>The <PROT2_5478>  CypA </PROT2_5478> - <PROT1_155030>  Gag </PROT1_155030> interaction can be blocked by an immunosuppressive drug , cyclosporine A ( CsA ) , and its analogues ( CITATION , CITATION , CITATION ) , and this manipulation inhibits the replication of most HIV - 1 strains in most cells in vitro ( CITATION , CITATION , CITATION , CITATION , CITATION , CITATION , CITATION , CITATION , CITATION , TARGET_CITATION ) . ||12032547_155030_5478==>Comparison of the NMR structures of the N - terminal domains of mature CA and the immature form ( covalently linked to <PROT1_155030>  matrix </PROT1_155030> ( MA ) ) ( TARGET_CITATION ) indicates that formation of the & # 223 ; - hairpin at the N terminus of mature CA , which occurs following proteolytic cleavage of <PROT1_155030>  Gag </PROT1_155030> ( CITATION , CITATION ) , induces both an ~2 - & Aring ; displacement of helix VI and displacement of the cyclophilin A ( <PROT2_5478>  CypA </PROT2_5478> ) binding loop ( fig. 1 ) . ||12032547_155030_5478==>X - ray and nuclear magnetic resonance analysis of <PROT2_5478>  CypA </PROT2_5478> in complex with various <PROT1_155030>  Gag </PROT1_155030> fragments confirmed that these residues participate in direct protein - protein interactions ( CITATION , CITATION , TARGET_CITATION , CITATION , CITATION ) . ||12525642_155807_7374==>We demonstrate that the <PROT1_155807>  Vpr </PROT1_155807> - dependent incorporation of <PROT2_7374>  UNG </PROT2_7374> into HIV - 1 particles is directly responsible for the role of <PROT1_155807>  Vpr </PROT1_155807> in the in vivo modulation of the virus mutation rate ( CITATION , TARGET_CITATION ) . ||12598123_155030_7251==><PROT2_7251>  Tsg101 </PROT2_7251> has been implicated in the budding of HIV - 1 and Ebola virus through its interaction with the PTAP motif present in the L domains of <PROT1_155030>  Gag </PROT1_155030> and VP40 , respectively ( TARGET_CITATION , CITATION ) . ||12598123_155030_7251==>The ability of TSG - 5 ' to inhibit virus budding without any apparent adverse effect on cellular sorting machinery demonstrates that antiviral agents can be developed that interfere with virus replication by specifically targeting the <PROT1_155030>  Gag </PROT1_155030> / <PROT2_7251>  TSG101 </PROT2_7251> interaction ( TARGET_CITATION ) . ||12598123_155030_7251==><PROT2_7251>  Tsg101 </PROT2_7251> has been identified as a host cell factor that binds the PTAP motif within the p6 region of HIV - 1 <PROT1_155030>  Gag </PROT1_155030> ( TARGET_CITATION , CITATION , CITATION ) . ||12598123_155030_7251==>Recent studies indicated that <PROT1_155030>  Gag </PROT1_155030> interacts directly with <PROT2_7251>  Tsg101 </PROT2_7251> , a ubiquitin enzyme 2 variant family protein that is involved in vesicular sorting pathways in the cell , suggesting that <PROT1_155030>  Gag </PROT1_155030> may utilize components of this pathway to reach the plasma membrane ( TARGET_CITATION , CITATION , CITATION ) . ||12663786_155030_7251==>Moreover , expression of HIV - 1 <PROT1_155030>  Gag </PROT1_155030> or Ebola virus VP40 results in PTAP - dependent recruitment of <PROT2_7251>  Tsg101 </PROT2_7251> and VPS28 , another ESCRT - I component , to sites of particle assembly at the plasma membrane ( CITATION , TARGET_CITATION ) . ||12663786_155030_7251==>We have previously described constructs and assays that demonstrated that artificial tethering of <PROT2_7251>  Tsg101 </PROT2_7251> to sites of HIV - 1 particle assembly , by fusion to <PROT1_155030>  Gag </PROT1_155030> , reverses the HIV - 1 budding defect that results from mutational inactivation of the PTAP L - domain ( CITATION , TARGET_CITATION ) . ||12663786_155030_7251==>Because HIV - 1 <PROT1_155030>  Gag </PROT1_155030> efficiently multimerizes at the plasma membrane ( CITATION , CITATION ) , expression of a <PROT1_155030>  Gag </PROT1_155030> { delta } p6 protein that is fused to functional L - domain or is directly fused to <PROT2_7251>  Tsg101 </PROT2_7251> can functionally complement a PTAP - defective proviral construct , resulting in infectious virion production ( CITATION , TARGET_CITATION ) . ||12663786_155030_7251==>In contrast , we have previously shown that similar defects induced by point mutations in the PTAP motif could be reversed by <PROT1_155030>  Gag </PROT1_155030> { delta } p6 - <PROT2_7251>  Tsg101 </PROT2_7251> coexpression ( CITATION , TARGET_CITATION ) . ||12663786_155030_7251==>It has thus been proposed that viral <PROT1_155030>  Gag </PROT1_155030> proteins can delocalize <PROT2_7251>  Tsg101 </PROT2_7251> and the cellular MVB budding machinery to the site of virus budding at the plasma membrane ( Martin - Serrano et al. , 2001 CITATION ; Martin - Serrano et al. , 2003 TARGET_CITATION ) . ||12663786_155030_7251==>It is interesting that we observed a marked redistribution of <PROT2_7251>  Tsg101 </PROT2_7251> in the presence of <PROT1_155030>  Gag </PROT1_155030> , a finding that is consistent with recent studies by Martin - Serrano and colleagues ( TARGET_CITATION ) . ||12663786_155030_7251==>Functional interactions between <PROT2_7251>  TSG101 </PROT2_7251> and the PTAP motifs present in HIV - 1 <PROT1_155030>  Gag </PROT1_155030> and Ebola virus VP40 have now been well documented ( CITATION , CITATION , CITATION , CITATION , TARGET_CITATION , CITATION , CITATION , CITATION ) . ||12663786_155030_7251==>Relocalization of <PROT2_7251>  Tsg101 </PROT2_7251> - VPS37C Complexes to the Plasma Membrane by HIV - 1 <PROT1_155030>  Gag </PROT1_155030> & # 151 ; Previously , we have shown that <PROT2_7251>  Tsg101 </PROT2_7251> can be relocalized to sites of viral budding at the plasma membrane by HIV - 1 <PROT1_155030>  Gag </PROT1_155030> or Ebola virus <PROT1_155030>  matrix </PROT1_155030> proteins ( CITATION , TARGET_CITATION ) , both of which encode PTAP - type L domains . ||12743307_155030_7251==>Likewise , the same siRNAs accelerated virus release ( fig. 6E ) , and overexpression of Tal inhibited two previously described exocytosis activities of <PROT2_7251>  Tsg101 </PROT2_7251> ( fig. 6E ; data not shown ) , namely , elevation of <PROT1_155030>  Gag </PROT1_155030> ubiquitylation ( Myers and Allen 2002 CITATION ) and inhibition of VLP release ( Goila - Gaur et al. 2003 TARGET_CITATION ) . ||12743307_155030_7251==>It was subsequently observed ( TARGET_CITATION ) that a mutation in TSG - 5 ' that blocks the interaction between <PROT1_155030>  Gag </PROT1_155030> and <PROT2_7251>  TSG101 </PROT2_7251> ( the TYN - mutation ) disrupts the inhibitory activity of TSG - 5 ' . ||12743307_155030_7251==>Functional interactions between <PROT2_7251>  TSG101 </PROT2_7251> and the PTAP motifs present in HIV - 1 <PROT1_155030>  Gag </PROT1_155030> and Ebola virus VP40 have now been well documented ( CITATION , TARGET_CITATION , CITATION , CITATION , CITATION , CITATION , CITATION , CITATION ) . ||12900394_155030_7251==>Sundquist and colleagues approached the general problem of targeting of cargo to MVBs from the perspective of the <PROT2_7251>  Tsg101 </PROT2_7251> - recruiting sequence in HIV <PROT1_155030>  Gag </PROT1_155030> ( TARGET_CITATION ) . ||12900394_155030_7251==>Indeed , TARGET_CITATION ( in this issue ) show in a companion paper that the PSAP - containing part of Hrs can functionally replace the PTAP - containing part of the HIV <PROT1_155030>  Gag </PROT1_155030> protein in budding of viruslike particles from the plasma membrane , indicating that HIV <PROT1_155030>  Gag </PROT1_155030> mimics the <PROT2_7251>  Tsg101 </PROT2_7251> - recruiting effect of Hrs . ||12900394_155030_7251==>For example , mutant retroviral <PROT1_155030>  Gag </PROT1_155030> proteins that would otherwise be retained can bud from cells when fused directly to various proteins or domains that can recruit ESCRT - I , including ubiquitin ( CITATION ) , <PROT2_7251>  TSG101 </PROT2_7251> ( CITATION ) , VPS28 ( CITATION ) , and HRS ( TARGET_CITATION ) . ||12900394_155030_7251==><PROT1_155030>  Gag </PROT1_155030> has a sevenfold - higher affinity for <PROT2_7251>  TSG101 </PROT2_7251> than Hrs does and can effectively compete with Hrs for <PROT2_7251>  TSG101 </PROT2_7251> binding in vitro ( TARGET_CITATION ) . ||12900394_155030_7251==>Indeed , fusion of fragments of <PROT2_7251>  Tsg101 </PROT2_7251> or Hrs to an HIV - 1 <PROT1_155030>  Gag </PROT1_155030> protein ( TARGET_CITATION , CITATION , CITATION ) , or VPS28 to an HIV - 1 or EIAV <PROT1_155030>  Gag </PROT1_155030> protein ( CITATION ) , 2 can rescue a budding defect induced by mutation of the <PROT1_155030>  Gag </PROT1_155030> - encoded L domain motif . ||14505569_155030_7251==>Recently , the entire cellular protein network that participates in HIV - 1 budding was mapped , with <PROT2_7251>  TSG101 </PROT2_7251> and AIP1 identified as direct interaction partners of the <PROT1_155030>  Gag </PROT1_155030> p6 domain ( CITATION , TARGET_CITATION , CITATION ) . ||14505570_155030_7251==>Recently , the entire cellular protein network that participates in HIV - 1 budding was mapped , with <PROT2_7251>  TSG101 </PROT2_7251> and AIP1 identified as direct interaction partners of the <PROT1_155030>  Gag </PROT1_155030> p6 domain ( CITATION , CITATION , TARGET_CITATION ) . ||14519844_10015_155030==>They also demonstrate that the <PROT2_155030>  GAG </PROT2_155030> protein from membrane - containing viruses , such as HIV , binds to <PROT1_10015>  Alix </PROT1_10015> / <PROT1_10015>  AIP1 </PROT1_10015> , thereby recruiting the ESCRT machinery to allow budding of the virus from the cell surface ( TARGET_CITATION & # 150 ; CITATION ) . ||14519844_10015_155030==>Recently , the entire cellular protein network that participates in HIV - 1 budding was mapped , with TSG101 and <PROT1_10015>  AIP1 </PROT1_10015> identified as direct interaction partners of the <PROT2_155030>  Gag </PROT2_155030> p6 domain ( TARGET_CITATION , CITATION , CITATION ) . ||2017166_155908_4869==><PROT2_4869>  NPM </PROT2_4869> is known to be enriched in proliferating cells and thought to be involved in ribosome assembly and transport due to its localization to the granular region of the nucleolus ( CITATION ) . <PROT2_4869>  NPM </PROT2_4869> has been ascribed a number of diverse properties , including a potential role in proliferation due to its rapid increase in synthesis during mitogenic stimulation ( CITATION ) ; a role as a cytoplasmic / nuclear shuttle protein ( CITATION ) ; has DNA binding activity ( CITATION , CITATION ) ; relieves transcriptional repression by YY1 ( CITATION ) ; binds the HIV Type 1 <PROT1_155908>  Rev </PROT1_155908> protein ( TARGET_CITATION ) , the human T - cell leukemia virus - 1 Rex protein ( CITATION ) , and another cell cycle - regulated nucleolar protein p120 ( CITATION ) ; is a nuclear substrate of protein kinase C ( CITATION ) , mitotic cdc2 kinase ( CITATION ) , and casein kinase II ( CITATION ) ; can be ADP - ribosylated ( CITATION ) ; and the N - terminal region has been shown to be a part of a fusion protein with a tyrosine kinase , a result of a chromosomal rearrangement , in some non - Hodgkin 's lymphomas ( CITATION ) . ||2017166_155908_4869==>The RNA binding domain of <PROT1_155908>  rev </PROT1_155908> can interact either with the RRE or with the nucleolar <PROT2_4869>  B23 </PROT2_4869> protein , but not with both ( TARGET_CITATION ) . ||2017166_155908_4869==>In addition , protein NO38 / <PROT2_4869>  B23 </PROT2_4869> has been reported to possess ribonuclease activity ( CITATION ) and to associate with transcription factor YY1 ( CITATION ) , protein <PROT1_155908>  Rev </PROT1_155908> of HIV - 1 ( TARGET_CITATION ) , and nucleolar protein p120 ( CITATION ) , suggesting that this protein has multiple functions . ||2017166_155908_4869==>In discussing possible binding partners of protein NO29 , it should further be considered that the related protein NO38 / <PROT2_4869>  B23 </PROT2_4869> has been reported to bind to various other nucleolar proteins such as protein p120 ( CITATION ) or to the nonnucleolar transcription factor YY1 ( CITATION ) as well as to certain viral proteins such as <PROT1_155908>  Rev </PROT1_155908> and Tat of HIV - 1 or the human T - lymphocyte virus type I protein Rex ( TARGET_CITATION , CITATION ) . ||2017166_155908_4869==>The NLS of <PROT1_155908>  Rev </PROT1_155908> has been reported to associate with importin beta , the large subunit of the conventional importin alpha / importin beta NLS receptor heterodimer , as well as with <PROT2_4869>  B23 </PROT2_4869> , a mammalian protein involved in the nuclear import of ribosomal proteins ( TARGET_CITATION ) . ||2017166_155908_4869==>The nucleolar localization signal of human T - cell leukemia virus type 1 Rex and human immunodeficiency virus type 1 <PROT1_155908>  Rev </PROT1_155908> binds specifically to the nucleolar shuttle phosphoprotein <PROT2_4869>  B23 </PROT2_4869> ( CITATION , TARGET_CITATION ) . ||2017166_155908_4869==>In the case of HIV - 1 <PROT1_155908>  Rev </PROT1_155908> , Fankhauser et al. ( TARGET_CITATION ) have proposed that the nucleolar protein <PROT2_4869>  B23 </PROT2_4869> binds to the <PROT1_155908>  Rev </PROT1_155908> basic domain and mediates its nuclear import . ||2017166_155908_4869==>In addition , our data confirm the observation by Henderson and Percipalle ( CITATION ) that the <PROT1_155908>  Rev </PROT1_155908> NLS can directly bind Imp beta and now show , for the first time , that <PROT1_155908>  Rev </PROT1_155908> NLS function is indeed independent of Imp alpha . Finally , we have not observed any evidence in support of the hypothesis of Fankhauser et al. ( TARGET_CITATION ) that <PROT1_155908>  Rev </PROT1_155908> NLS function is mediated by the <PROT2_4869>  B23 </PROT2_4869> protein . ||2017166_155908_4869==>Protein <PROT2_4869>  B23 </PROT2_4869> interacts with other nucleolar proteins , including nucleolin ( CITATION ) , protein p120 ( CITATION ) , and the HIV - 1 <PROT1_155908>  Rev </PROT1_155908> protein ( TARGET_CITATION ) . ||2017166_155908_4869==><PROT2_4869>  B23 </PROT2_4869> has also been reported to bind the arginine - rich basic region of the human T - cell leukemia virus protein Rex ( CITATION ) , and the HIV proteins <PROT1_155908>  Rev </PROT1_155908> ( TARGET_CITATION , CITATION ) and Tat ( CITATION ) . ||2017166_155908_4869==>Furthermore , it is shown that <PROT2_4869>  B23 </PROT2_4869> protein binds a wide diversity of proteins , such as nucleolar phosphoproteins , nucleolin and p120 ( Durban et al. , 1995 CITATION ; Li et al. , 1996 CITATION ) , HIV1 - <PROT1_155908>  Rev </PROT1_155908> protein ( Fankhauser et al. , 1991 TARGET_CITATION ) , retinoblastoma protein ( Takemura et al. , 1999 CITATION ) to stimulate the DNA polymerase alpha activity ( Umekawa et al. , 2001 CITATION ) , and hepatitis delta virus delta antigens ( Huang et al. , 2001 CITATION ) . ||2017166_155908_4869==>Protein <PROT2_4869>  B23 </PROT2_4869> binds RNA and DNA ( CITATION ) and interacts with other nucleolar proteins , including nucleolin ( CITATION ) , protein P120 ( CITATION ) , and the HIV - 1 <PROT1_155908>  Rev </PROT1_155908> protein ( TARGET_CITATION , CITATION ) . ||2017166_155908_4869==>Earlier experiments ( TARGET_CITATION , CITATION ) showed that there is a strong affinity between nonphosphorylated protein <PROT2_4869>  B23 </PROT2_4869> and the HIV <PROT1_155908>  Rev </PROT1_155908> protein and that protein <PROT2_4869>  B23 </PROT2_4869> also acts as a molecular chaperone toward <PROT1_155908>  Rev </PROT1_155908> ( CITATION ) . ||2017166_155908_4869==>To examine the speckle pattern of mutant DD in greater detail , we analyzed DD - transfected cells by confocal microscopy after staining them with the anti - Rex - 2 antibody , an antibody against the nuclear envelope component Nup62 ( added to delineate the nucleus ) , and an antibody recognizing <PROT2_4869>  B23 </PROT2_4869> , a multifunctional nucleolar protein that is proposed to act as a chaperone for nuclear import , nucleolar accumulation , and functional activity of <PROT1_155908>  Rev </PROT1_155908> and Rex ( TARGET_CITATION , CITATION , CITATION - CITATION ) . ||2017166_155908_4869==>Nucleophosmin & # 47 ; <PROT2_4869>  B23 </PROT2_4869> , being more abundant in tumour cells than in normal resting cells , has a potential role in increased nucleolar activity that is necessary for cell proliferation ( CITATION ; CITATION ) ; a role as a cytoplasmic & # 47 ; nuclear shuttle protein ( CITATION ) ; relieves transcription repression by YY1 ( CITATION ) ; binds nuclear and nucleolar localisation signals on the HIV Type 1 <PROT1_155908>  Rev </PROT1_155908> protein ( TARGET_CITATION ) and the human T - cell leukaemia virus - 1 - Rex protein ( CITATION ) ; binds cell cycle - regulated nucleolar protein p120 ( CITATION ) ; inhibits DNA - binding and transcriptional activity of interferon regulatory factor - 1 ( IRF - 1 ) , which is a tumour suppressor ( CITATION ; CITATION ) . ||2017166_155908_4869==>The NLS of <PROT1_155908>  Rev </PROT1_155908> has been reported to associate with importin { beta } , as well as with <PROT2_4869>  B23 </PROT2_4869> , a protein involved in the nuclear import of ribosomal proteins ( CITATION , TARGET_CITATION ) . ||7634337_155908_7514==>Indeed , various cellular proteins which appear to be specific binding partners of the <PROT1_155908>  Rev </PROT1_155908> activation domain have been described ; these include nucleoporin - like protein hRIP / Rab ( TARGET_CITATION , CITATION ) , eukaryotic initiation factor 5A ( eIF - 5A ) ( CITATION ) , and nuclear export factor <PROT2_7514>  CRM1 </PROT2_7514> , which appears to be a general nuclear export signal receptor ( CITATION , CITATION , CITATION , CITATION ) . ||7634337_155908_7514==>These cofactors , including nucleoporin - like proteins such as hRIP / Rab ( TARGET_CITATION , CITATION , CITATION ) , <PROT2_7514>  CRM1 </PROT2_7514> ( CITATION , CITATION , CITATION , CITATION ) , and nuclear eIF - 5A ( CITATION , CITATION ) , are thought to mediate the subsequent nuclear export of <PROT1_155908>  Rev </PROT1_155908> ( reviewed in reference CITATION ) . ||7634337_155908_7514==>In fact , various proteins that are able to bind to this region have been described , including eukaryotic initiation factor 5A ( eIF - 5A ) ( CITATION ) , the nucleoporin - like protein human <PROT1_155908>  Rev </PROT1_155908> interacting protein ( hRIP ) / Rab ( CITATION , TARGET_CITATION ) and , more recently , the nuclear pore - associated factor <PROT2_7514>  CRM1 </PROT2_7514> ( CITATION ) that is critically involved in the translocation of NES - containing proteins through the nuclear pore complex ( CITATION ) . ||7634337_155908_7514==>Hrb is thought to be a recruiter of <PROT1_155908>  Rev </PROT1_155908> to the nuclear pore , either directly ( Bogerd et al. 1995 TARGET_CITATION ) or , more likely , through interaction with <PROT2_7514>  Crm1 </PROT2_7514> ( Neville et al. 1997 CITATION ) . ||7634337_155908_7514==>Nup42 was originally identified as a <PROT1_155908>  Rev </PROT1_155908> - interacting protein in a yeast two - hybrid screen or a copper resistance assay ( TARGET_CITATION , CITATION ) , and the interaction was shown to be mediated by <PROT2_7514>  Crm1 </PROT2_7514> ( CITATION ) . ||7634337_155908_7514==>In the Saccharomyces cerevisiae two - hybrid system , it has been shown that FG - containing repeat domains of different nucleoporins interact with the <PROT1_155908>  Rev </PROT1_155908> NES via <PROT2_7514>  CRM1 </PROT2_7514> with various efficiencies , suggesting that nucleoporins play a role in NES - mediated export ( TARGET_CITATION , CITATION , CITATION , CITATION , CITATION ) . ||7634337_155908_7514==>In contrast , however , the nucleoporin - like protein hRIP / Rab ( TARGET_CITATION , CITATION ) was shown to bind indirectly via <PROT2_7514>  CRM1 </PROT2_7514> / exportin 1 to the <PROT1_155908>  Rev </PROT1_155908> NES ( CITATION ) . ||7634337_155908_7514==>The NES mediates association of <PROT1_155908>  Rev </PROT1_155908> with the general nuclear export factor <PROT2_7514>  CRM1 </PROT2_7514> / exportin1 ( CITATION , CITATION , CITATION , CITATION ) , the nucleoporin - like protein Rab1 / hRIP ( TARGET_CITATION , CITATION ) , and the eukaryotic initiation factor 5A ( eIF5A ) ( CITATION ) , and it is responsible for directing <PROT1_155908>  Rev </PROT1_155908> - RNA complexes through an export pathway used by 5S rRNA and U snRNAs ( CITATION ) . ||7634337_155908_7514==>Several cellular factors have been identified to be directly involved in the <PROT1_155908>  Rev </PROT1_155908> - mediated nuclear export pathway , such as <PROT2_7514>  CRM1 </PROT2_7514> ( CITATION , CITATION ) , eukaryotic initiation factor 5A ( eIF - 5A ) ( CITATION ) , and Rip / Rab ( TARGET_CITATION , CITATION ) . ||7634337_155908_7514==>Several cellular factors have been identified as involved in the <PROT1_155908>  Rev </PROT1_155908> - mediated nuclear export pathway ; these include <PROT2_7514>  CRM1 </PROT2_7514> ( CITATION , CITATION ) , eIF5 - A ( CITATION ) , and Rip / Rab ( TARGET_CITATION , CITATION ) . ||7634337_155908_7514==>Several putative cofactors for <PROT1_155908>  Rev </PROT1_155908> NES function have been identified ; particularly well - documented ones include nucleoporins such as Rab / hRIP and Rip1p ( TARGET_CITATION , CITATION , CITATION ) and the nucleocytoplasmic shuttle protein <PROT2_7514>  CRM1 </PROT2_7514> ( CITATION , CITATION , CITATION ) . ||7637788_155908_3267==>Nucleotide sequence of the longest phage inserts of these cDNAs revealed that they represented partial cDNAs of the human homolog of NUMB , a developmentally regulated gene of Drosophila ( Uemura et al. 1989 CITATION ) ; a NUMB - related gene , which we named NUMB - R ; <PROT2_3267>  RAB </PROT2_3267> , coding the cellular cofactor of the HIV <PROT1_155908>  REV </PROT1_155908> protein ( Bogerd et al. 1995 CITATION ; Fritz et al. 1995 TARGET_CITATION ) ; and a <PROT2_3267>  RAB </PROT2_3267> - related gene , which we named <PROT2_3267>  RAB </PROT2_3267> - R ( see next section ) . ||7637788_155908_3267==>Although <PROT1_155908>  Rev </PROT1_155908> interacts efficiently with Rip1p and hRIP / <PROT2_3267>  Rab </PROT2_3267> in two - hybrid assays ( Bogerd et al. 1995 CITATION ; Fritz et al. 1995 TARGET_CITATION ; Stutz et al. 1995 CITATION ) , the ability of mutant <PROT1_155908>  Rev </PROT1_155908> activation domains to function in vivo closely correlates with their ability to interact with hRIP / <PROT2_3267>  Rab </PROT2_3267> / Rip1p in two - hybrid assays ( Bogerd et al. 1995 CITATION ; Stutz et al. 1996 CITATION ) . ||7637788_155908_3267==>The <PROT1_155908>  rev </PROT1_155908> NES has been reported to interact with several different cellular factors , including the protein termed <PROT2_3267>  Rab </PROT2_3267> ( CITATION ) or hRIP ( TARGET_CITATION ) . ||7637788_155908_3267==>Nuclear pore proteins may also act as a receptor for factors involved in export reactions , since a cellular protein ( <PROT2_3267>  Rab </PROT2_3267> / hRip ) , which contains several FG repeat sequences typically found in nucleoporins , binds to a nuclear export sequence ( NES ) of the HIV <PROT1_155908>  Rev </PROT1_155908> protein which , itself , exports unspliced and partially spliced viral mRNA from the nucleus to the cytoplasm ( CITATION ; CITATION ; TARGET_CITATION ) . ||7637788_155908_3267==>The <PROT1_155908>  Rev </PROT1_155908> protein has been proposed to interact with several cellular proteins such as the <PROT1_155908>  Rev </PROT1_155908> - interacting protein ( <PROT2_3267>  Rip </PROT2_3267> or <PROT2_3267>  Rab </PROT2_3267> ) ( CITATION ; TARGET_CITATION ; CITATION ) , eukaryotic initiation factor 5A ( eIF5A ) ( CITATION ; CITATION ) and proteins of the nuclear pore complex ( NPC ) ( CITATION , CITATION ; CITATION ) . ||7637788_155908_3267==>Nucleoporin - like proteins hRip / <PROT2_3267>  Rab </PROT2_3267> have been shown to interact with the NES of <PROT1_155908>  Rev </PROT1_155908> and are believed to be involved in the nuclear export of <PROT1_155908>  Rev </PROT1_155908> ( CITATION , TARGET_CITATION ) . ||7637788_155908_3267==>In yeast two - hybrid experiments , NESs have been shown to interact , perhaps indirectly , with a variety of proteins such as the <PROT1_155908>  Rev </PROT1_155908> - interacting proteins ( hRip / <PROT2_3267>  Rab </PROT2_3267> ) ( CITATION - TARGET_CITATION ) and several yeast and vertebrate nucleoporins ( nuclear pore proteins ; refs. CITATION , CITATION , CITATION ) . ||7637788_155908_3267==>These transport effects could involve the specific interplay of other cellular factors , such as the nucleoporin - like <PROT2_3267>  Rab </PROT2_3267> / <PROT2_3267>  Rip </PROT2_3267> proteins ( CITATION - TARGET_CITATION ) or eIF 5A ( CITATION , CITATION ) , with the leucine - rich activation domain of <PROT1_155908>  Rev </PROT1_155908> ( CITATION ) , which functions as a nuclear export signal ( CITATION , CITATION ) . ||7637788_155908_3267==>Using the yeast two - hybrid system , a human protein called <PROT2_3267>  Rip </PROT2_3267> ( Fritz et al. 1995 TARGET_CITATION ) or <PROT2_3267>  Rab </PROT2_3267> ( Bogerd et al. 1995 CITATION ) that interacted specifically with <PROT1_155908>  Rev </PROT1_155908> was identified . ||7637788_155908_3267==>The <PROT1_155908>  Rev </PROT1_155908> effector domain contains a nuclear export signal ( NES ) and interacts with the nucleoporin <PROT2_3267>  Rab </PROT2_3267> / <PROT2_3267>  Rip </PROT2_3267> , a protein that mediate nucleocytoplasmic transport ( TARGET_CITATION ) . ||7637788_155908_3267==>They comprised three different , incomplete sequences : two were novel , and the other was identified as the murine homolog of the <PROT1_155908>  Rev </PROT1_155908> - associated binding / <PROT1_155908>  Rev </PROT1_155908> - interacting protein ( <PROT2_3267>  RAB </PROT2_3267> / <PROT2_3267>  Rip </PROT2_3267> ) ( CITATION , TARGET_CITATION ) . ||7637788_155908_3267==>These proteins include the human homologue of the Drosophila NUMB protein ( h - NUMB , refs. CITATION ) , a numb related protein ( h - NUMB - R , ref. CITATION ) , the cellular co - factor of the HIV <PROT1_155908>  REV </PROT1_155908> protein , <PROT2_3267>  RAB </PROT2_3267> ( h - <PROT2_3267>  RAB </PROT2_3267> , refs. CITATION and TARGET_CITATION ) , and a <PROT2_3267>  RAB </PROT2_3267> - related gene ( h - <PROT2_3267>  RAB </PROT2_3267> - R , ref. CITATION ) . ||7637788_155908_3267==>In particular , we note that <PROT2_3267>  RAB </PROT2_3267> , the cellular co - factor of the HIV <PROT1_155908>  REV </PROT1_155908> protein , is an EH interactor that binds to eps15R and exhibits structural and topographical features compatible with those of a nucleoporin ( CITATION , TARGET_CITATION ) . ||7637788_155908_3267==>Initial efforts to define the nuclear export pathway utilized by HIV - 1 <PROT1_155908>  Rev </PROT1_155908> led to the demonstration that the <PROT1_155908>  Rev </PROT1_155908> NES could interact specifically with a cellular nucleoporin - like protein termed hRIP / <PROT2_3267>  Rab </PROT2_3267> in both yeast and mammalian two - hybrid assays ( CITATION , TARGET_CITATION , CITATION ) . ||7637788_155908_3267==>The hRIP / <PROT2_3267>  Rab </PROT2_3267> protein proved able to interact with <PROT1_155908>  Rev </PROT1_155908> when <PROT1_155908>  Rev </PROT1_155908> was bound to the RRE and also specifically bound NESs found in HTLV - 1 Rex and in other , distinct <PROT1_155908>  Rev </PROT1_155908> proteins , such as visna maedi virus ( VMV ) <PROT1_155908>  Rev </PROT1_155908> . Significantly , overexpression of hRIP / <PROT2_3267>  Rab </PROT2_3267> was observed to modestly enhance <PROT1_155908>  Rev </PROT1_155908> function when <PROT1_155908>  Rev </PROT1_155908> expression was limiting or when a <PROT1_155908>  Rev </PROT1_155908> protein bearing an attenuated NES was used ( CITATION , TARGET_CITATION ) . ||7637788_155908_3267==>To further confirm that hCrm1 binding indeed fully correlates with NES function , as also previously demonstrated for hRIP / <PROT2_3267>  Rab </PROT2_3267> binding ( CITATION , CITATION , CITATION , CITATION , TARGET_CITATION , CITATION ) , we examined the ability of hCrm1 to bind to wild - type and NES mutant forms of HIV - 1 <PROT1_155908>  Rev </PROT1_155908> , HTLV - I Rex , and VMV <PROT1_155908>  Rev </PROT1_155908> in a mammalian two - hybrid assay . ||7637788_155908_3267==>This laboratory has previously described ( CITATION ) an extensive set of point missense mutations within the <PROT1_155908>  Rev </PROT1_155908> NES , and it has been demonstrated , by both ourselves and others , that the activity of these NES mutants completely correlates with their ability to bind hRIP / <PROT2_3267>  Rab </PROT2_3267> , as well as certain other nucleoporins such as Nup214 / CAN , in the yeast two - hybrid assay ( CITATION , CITATION , TARGET_CITATION , CITATION , CITATION ) . ||7637788_155908_3267==>The demonstration of a specific interaction between the <PROT1_155908>  Rev </PROT1_155908> NES and hRIP / <PROT2_3267>  Rab </PROT2_3267> , as well as several cellular nucleoporins , in both the yeast and mammalian two - hybrid assays ( CITATION , TARGET_CITATION , CITATION ) appeared to represent an important step forward in understanding how leucine - rich NESs function , given the known importance of nucleoporins in the regulation of nucleocytoplasmic transport ( CITATION , CITATION ) . ||7637788_155908_3267==>Indeed , various cellular proteins which appear to be specific binding partners of the <PROT1_155908>  Rev </PROT1_155908> activation domain have been described ; these include nucleoporin - like protein hRIP / <PROT2_3267>  Rab </PROT2_3267> ( CITATION , TARGET_CITATION ) , eukaryotic initiation factor 5A ( eIF - 5A ) ( CITATION ) , and nuclear export factor CRM1 , which appears to be a general nuclear export signal receptor ( CITATION , CITATION , CITATION , CITATION ) . ||7637788_155908_3267==>These cofactors , including nucleoporin - like proteins such as hRIP / <PROT2_3267>  Rab </PROT2_3267> ( CITATION , TARGET_CITATION , CITATION ) , CRM1 ( CITATION , CITATION , CITATION , CITATION ) , and nuclear eIF - 5A ( CITATION , CITATION ) , are thought to mediate the subsequent nuclear export of <PROT1_155908>  Rev </PROT1_155908> ( reviewed in reference CITATION ) . ||7637788_155908_3267==>In fact , various proteins that are able to bind to this region have been described , including eukaryotic initiation factor 5A ( eIF - 5A ) ( CITATION ) , the nucleoporin - like protein human <PROT1_155908>  Rev </PROT1_155908> interacting protein ( hRIP ) / <PROT2_3267>  Rab </PROT2_3267> ( TARGET_CITATION , CITATION ) and , more recently , the nuclear pore - associated factor CRM1 ( CITATION ) that is critically involved in the translocation of NES - containing proteins through the nuclear pore complex ( CITATION ) . ||7637788_155908_3267==>In particular , the EH network might be involved in the control of nucleocytoplasmic export , as suggested by the finding that three EH - containing proteins , Eps15 , Eps15R , and intersectin , interact with <PROT2_3267>  Hrb </PROT2_3267> ( also called hRip or <PROT2_3267>  RAB </PROT2_3267> , Human Gene Nomenclature Committee approved symbols are used in this paper ) , a cellular cofactor for the HIV - 1 <PROT1_155908>  Rev </PROT1_155908> protein ( Bogerd et al. 1995 CITATION ; Fritz et al. 1995 TARGET_CITATION ) , and with the related protein Hrbl ( Salcini et al. 1997 CITATION ; Yamabhai et al. 1998 CITATION ) . ||7637788_155908_3267==>Efforts to identify cellular cofactors mediating <PROT1_155908>  Rev </PROT1_155908> export led to the isolation of the distantly related human <PROT2_3267>  Hrb </PROT2_3267> ( Bogerd et al. 1995 CITATION ; Fritz et al. 1995 TARGET_CITATION ) and yeast Rip1p ( Stutz et al. 1995 CITATION ) proteins , which were shown to enhance <PROT1_155908>  Rev </PROT1_155908> function in cells . ||7637788_155908_3267==>A yeast two - hybrid screen initially identified the yeast FG - nucleoporin Rip1p and the non - homologous mammalian protein hRip / <PROT2_3267>  RAB </PROT2_3267> as potential targets for <PROT1_155908>  Rev </PROT1_155908> - NES at the nuclear pore ( CITATION ; TARGET_CITATION ; CITATION ) . ||7637788_155908_3267==>A human nucleoporin - like protein called hRIP / <PROT2_3267>  Rab </PROT2_3267> in human and a new yeast nuclear pore - associated protein , <PROT2_3267>  Rip </PROT2_3267> - 1p , were shown to interact specifically with functional NES , which was consistent with a role of <PROT1_155908>  Rev </PROT1_155908> in nuclear export of RNA ( TARGET_CITATION ) . ||7637788_155908_3267==>It has been reported recently that both HIV - 1 <PROT1_155908>  Rev </PROT1_155908> and HTLV - 1 Rex interact in the yeast two - hybrid system with a nucleoporin - like human protein called hRIP / <PROT2_3267>  Rab </PROT2_3267> and several yeast and mammalian FG - rich nucleoporins including yRip1p , hNup214 , and hNup153 ( TARGET_CITATION ) . ||7637788_155908_3267==>Thus , NLP - 1 closely resembles the previously identified <PROT1_155908>  Rev </PROT1_155908> - interacting protein hRIP / <PROT2_3267>  Rab </PROT2_3267> , which also harbors many FG repeats , a high serine content , and a zinc finger of the CCCC type ( TARGET_CITATION , CITATION ) . ||7637788_155908_3267==>CRM - 1 probably bridges the indirect interaction of <PROT1_155908>  Rev </PROT1_155908> with members of the nucleoporin family CITATION , including <PROT2_3267>  Rab </PROT2_3267> / hRIP , reported to be <PROT1_155908>  Rev </PROT1_155908> - binding proteins CITATION , TARGET_CITATION . ||7637788_155908_3267==>In contrast , however , the nucleoporin - like protein hRIP / <PROT2_3267>  Rab </PROT2_3267> ( CITATION , TARGET_CITATION ) was shown to bind indirectly via CRM1 / exportin 1 to the <PROT1_155908>  Rev </PROT1_155908> NES ( CITATION ) . ||7637788_155908_3267==><PROT2_3267>  Rip </PROT2_3267> / <PROT2_3267>  Rab </PROT2_3267> is an HIV <PROT1_155908>  Rev </PROT1_155908> - binding protein with FG repeat motifs ( Bogerd et al. , 1995 CITATION ; Fritz et al. , 1995 TARGET_CITATION ; Stutz et al. , 1995 CITATION ) . ||7637788_155908_3267==>The N - terminal ( DI ) domain contains three copies of the evolutionary conserved EH domain ( CITATION ) , a protein - protein binding module that recognizes NPF ( asparagine - proline - phenylalanine ) motifs ( CITATION ) present in several proteins including the epsins ( CITATION , CITATION ) and <PROT2_3267>  Hrb </PROT2_3267> / hRIP / <PROT2_3267>  RAB </PROT2_3267> ( CITATION ) , a protein involved in the nuclear export of the HIV <PROT1_155908>  Rev </PROT1_155908> protein ( CITATION - TARGET_CITATION ) . ||7637788_155908_3267==>Several cellular factors have been identified to be directly involved in the <PROT1_155908>  Rev </PROT1_155908> - mediated nuclear export pathway , such as CRM1 ( CITATION , CITATION ) , eukaryotic initiation factor 5A ( eIF - 5A ) ( CITATION ) , and <PROT2_3267>  Rip </PROT2_3267> / <PROT2_3267>  Rab </PROT2_3267> ( CITATION , TARGET_CITATION ) . ||7637788_155908_3267==>Several cellular factors have been identified as involved in the <PROT1_155908>  Rev </PROT1_155908> - mediated nuclear export pathway ; these include CRM1 ( CITATION , CITATION ) , eIF5 - A ( CITATION ) , and <PROT2_3267>  Rip </PROT2_3267> / <PROT2_3267>  Rab </PROT2_3267> ( CITATION , TARGET_CITATION ) . ||7637788_155908_3267==>Several putative cofactors for <PROT1_155908>  Rev </PROT1_155908> NES function have been identified ; particularly well - documented ones include nucleoporins such as <PROT2_3267>  Rab </PROT2_3267> / hRIP and Rip1p ( CITATION , TARGET_CITATION , CITATION ) and the nucleocytoplasmic shuttle protein CRM1 ( CITATION , CITATION , CITATION ) . ||7637788_155908_3267==>The human <PROT1_155908>  Rev </PROT1_155908> - interacting protein ( hRIP ) , also known as hRab or <PROT2_3267>  Hrb </PROT2_3267> , was identified using a yeast two - hybrid screen with <PROT1_155908>  Rev </PROT1_155908> as the bait ( Bogerd et al. 1995 CITATION ; Fritz et al. 1995 TARGET_CITATION ) . ||7637788_155908_3267==>Most of these ligands are already known , but a number of new ligands including the HIV - 1 <PROT1_155908>  Rev </PROT1_155908> interacting protein ( <PROT2_3267>  RIP </PROT2_3267> ) , important for nuclear export of viral RNA and infectivity ( TARGET_CITATION ) , are discussed in Supplementary Table 1 . ||7637788_155908_7514==>Indeed , various cellular proteins which appear to be specific binding partners of the <PROT1_155908>  Rev </PROT1_155908> activation domain have been described ; these include nucleoporin - like protein hRIP / Rab ( CITATION , TARGET_CITATION ) , eukaryotic initiation factor 5A ( eIF - 5A ) ( CITATION ) , and nuclear export factor <PROT2_7514>  CRM1 </PROT2_7514> , which appears to be a general nuclear export signal receptor ( CITATION , CITATION , CITATION , CITATION ) . ||7637788_155908_7514==>These cofactors , including nucleoporin - like proteins such as hRIP / Rab ( CITATION , TARGET_CITATION , CITATION ) , <PROT2_7514>  CRM1 </PROT2_7514> ( CITATION , CITATION , CITATION , CITATION ) , and nuclear eIF - 5A ( CITATION , CITATION ) , are thought to mediate the subsequent nuclear export of <PROT1_155908>  Rev </PROT1_155908> ( reviewed in reference CITATION ) . ||7637788_155908_7514==>In fact , various proteins that are able to bind to this region have been described , including eukaryotic initiation factor 5A ( eIF - 5A ) ( CITATION ) , the nucleoporin - like protein human <PROT1_155908>  Rev </PROT1_155908> interacting protein ( hRIP ) / Rab ( TARGET_CITATION , CITATION ) and , more recently , the nuclear pore - associated factor <PROT2_7514>  CRM1 </PROT2_7514> ( CITATION ) that is critically involved in the translocation of NES - containing proteins through the nuclear pore complex ( CITATION ) . ||7637788_155908_7514==>In the Saccharomyces cerevisiae two - hybrid system , it has been shown that FG - containing repeat domains of different nucleoporins interact with the <PROT1_155908>  Rev </PROT1_155908> NES via <PROT2_7514>  CRM1 </PROT2_7514> with various efficiencies , suggesting that nucleoporins play a role in NES - mediated export ( CITATION , CITATION , TARGET_CITATION , CITATION , CITATION ) . ||7637788_155908_7514==>In contrast , however , the nucleoporin - like protein hRIP / Rab ( CITATION , TARGET_CITATION ) was shown to bind indirectly via <PROT2_7514>  CRM1 </PROT2_7514> / exportin 1 to the <PROT1_155908>  Rev </PROT1_155908> NES ( CITATION ) . ||7637788_155908_7514==>The NES mediates association of <PROT1_155908>  Rev </PROT1_155908> with the general nuclear export factor <PROT2_7514>  CRM1 </PROT2_7514> / exportin1 ( CITATION , CITATION , CITATION , CITATION ) , the nucleoporin - like protein Rab1 / hRIP ( CITATION , TARGET_CITATION ) , and the eukaryotic initiation factor 5A ( eIF5A ) ( CITATION ) , and it is responsible for directing <PROT1_155908>  Rev </PROT1_155908> - RNA complexes through an export pathway used by 5S rRNA and U snRNAs ( CITATION ) . ||7637788_155908_7514==>For both HIV - 1 <PROT1_155908>  Rev </PROT1_155908> and influenza A virus NEP , a positive correlation has previously been demonstrated for the ability to bind particular nucleoporins and <PROT2_7514>  Crm1 </PROT2_7514> in yeast and / or mammalian two - hybrid systems and function as a nuclear export chaperon ( CITATION , CITATION , TARGET_CITATION , CITATION , CITATION , CITATION , CITATION , CITATION , CITATION ) . ||7637788_155908_7514==>Several cellular factors have been identified to be directly involved in the <PROT1_155908>  Rev </PROT1_155908> - mediated nuclear export pathway , such as <PROT2_7514>  CRM1 </PROT2_7514> ( CITATION , CITATION ) , eukaryotic initiation factor 5A ( eIF - 5A ) ( CITATION ) , and Rip / Rab ( CITATION , TARGET_CITATION ) . ||7637788_155908_7514==>Several cellular factors have been identified as involved in the <PROT1_155908>  Rev </PROT1_155908> - mediated nuclear export pathway ; these include <PROT2_7514>  CRM1 </PROT2_7514> ( CITATION , CITATION ) , eIF5 - A ( CITATION ) , and Rip / Rab ( CITATION , TARGET_CITATION ) . ||7637788_155908_7514==>Several putative cofactors for <PROT1_155908>  Rev </PROT1_155908> NES function have been identified ; particularly well - documented ones include nucleoporins such as Rab / hRIP and Rip1p ( CITATION , TARGET_CITATION , CITATION ) and the nucleocytoplasmic shuttle protein <PROT2_7514>  CRM1 </PROT2_7514> ( CITATION , CITATION , CITATION ) . ||7778269_155871_22954==>These proteins include TATA - binding protein ( TBP ) ( CITATION , CITATION ) , TAK ( CITATION , CITATION ) , PKR ( CITATION , CITATION ) , T3R ( CITATION ) , <PROT1_155871>  Tat </PROT1_155871> - binding protein 1 ( CITATION , CITATION ) , TAP ( CITATION , CITATION , CITATION ) , TBP - associated factor TAF55 ( CITATION ) , <PROT2_22954>  HT2A </PROT2_22954> ( TARGET_CITATION ) , Tip60 ( CITATION ) , TFIIH ( CITATION , CITATION ) , RNA polymerase II ( CITATION ) , and Sp1 ( CITATION , CITATION ) . ||7778269_155871_22954==>Earlier - reported candidates for <PROT1_155871>  Tat </PROT1_155871> - interacting cofactors include TBP1 ( CITATION ) , TAP ( CITATION ) , Tip60 ( CITATION ) , and <PROT2_22954>  HT2A </PROT2_22954> ( TARGET_CITATION ) . ||7778269_155871_22954==>It was identified in a yeast two - hybrid screening for proteins that interact with the human immunodeficiency virus protein <PROT1_155871>  Tat </PROT1_155871> , and the last 120 amino acids of <PROT2_22954>  HT2A </PROT2_22954> were sufficient for <PROT1_155871>  Tat </PROT1_155871> binding ( TARGET_CITATION ) . ||7778269_155871_22954==>The C - terminal region of <PROT2_22954>  HT2A </PROT2_22954> was used as a positive control and interacted strongly with <PROT1_155871>  Tat </PROT1_155871> , as reported by Fridell et al. ( TARGET_CITATION ) . ||7778269_155871_22954==>In addition to hCycT1 , a number of other potential <PROT1_155871>  Tat </PROT1_155871> interacting proteins and / or cofactors have been proposed including MSS1 , <PROT2_22954>  HT2A </PROT2_22954> , CA150 , TFIID , <PROT1_155871>  Tat </PROT1_155871> - SF1 , TIP30 , and PolII itself ( CITATION - TARGET_CITATION ) , and other groups have reported interactions between <PROT1_155871>  Tat </PROT1_155871> and the coactivator proteins p300 and CREB - binding protein ( CBP ) ( CITATION ) or between <PROT1_155871>  Tat </PROT1_155871> and the transcription factor TFIIH ( CITATION , CITATION , CITATION , CITATION ) . ||7778269_155871_22954==>Another subgroup includes F54G8.4 , a nematode ORF with unknown function , and the human <PROT2_22954>  HT2A </PROT2_22954> protein , identified through its interaction with the human immunodeficiency virus protein <PROT1_155871>  Tat </PROT1_155871> ( TARGET_CITATION ) . ||7778269_155871_22954==>All three factors have ties to RNA metabolism : the nucleoli in Caenorhabditis elegans ncl - 1 mutants are enlarged ( Frank and Roth 1998 CITATION ) ; <PROT2_22954>  HT2A </PROT2_22954> was identified by virtue of interaction with the RNA - binding protein HIV <PROT1_155871>  Tat </PROT1_155871> ( Fridell et al. 1995 TARGET_CITATION ) ; and posttranscriptional regulation of lin - 29 mRNA is abrogated in lin - 41 mutants ( Slack et al. 2000 CITATION ) . ||7778269_155871_22954==>First , the <PROT2_22954>  HT2A </PROT2_22954> human protein interacts with the site - specific RNA - binding <PROT1_155871>  Tat </PROT1_155871> protein ( Fridell et al. 1995 TARGET_CITATION ) , much as Brat interacts with Nos and Pum . ||7778269_155871_22954==>Besides cyclin T , other <PROT1_155871>  Tat </PROT1_155871> - interacting proteins and / or cofactors include Tip60 , <PROT2_22954>  HT2A </PROT2_22954> , CA150 , TFIID , <PROT1_155871>  Tat </PROT1_155871> - SF1 , Tip30 , p300 , and CBP ( CITATION , CITATION - TARGET_CITATION ) . ||7778269_155871_708==>Originally , <PROT2_708>  p32 </PROT2_708> was characterized as being a component of the ASF / SF2 splicing activity purified from HeLa cells ( CITATION ) . Subsequently , it was shown that <PROT2_708>  p32 </PROT2_708> was dispensable for the general splicing activity , although the possibility can not be ruled out that <PROT2_708>  p32 </PROT2_708> has a more specialized role in splicing ( CITATION ) . Recent evidence suggests that <PROT2_708>  p32 </PROT2_708> also interacts with the HIV - 1 <PROT1_155871>  Tat </PROT1_155871> protein ( CITATION , CITATION , TARGET_CITATION ) . In one report , a <PROT1_155871>  Tat </PROT1_155871> - binding protein ( TAP ) was isolated on the basis of <PROT1_155871>  Tat </PROT1_155871> affinity chromatography , and the sequence turned out to be identical to <PROT2_708>  p32 </PROT2_708> except for a few amino acids in the N - terminal precursor segment ( CITATION ) . The same group also found that TAP ( <PROT2_708>  p32 </PROT2_708> ) interacts with the C terminus of TFIIB , and it was suggested that TAP ( <PROT2_708>  p32 </PROT2_708> ) may function as a cellular co - activator that bridges <PROT1_155871>  Tat </PROT1_155871> to the general transcription machinery ( CITATION ) . The significance of the TAP ( <PROT2_708>  p32 </PROT2_708> ) - <PROT1_155871>  Tat </PROT1_155871> interaction was substantiated by a two - hybrid analysis , in vitro binding studies , and a demonstration implying that TAP ( <PROT2_708>  p32 </PROT2_708> ) was able to cooperate with <PROT1_155871>  Tat </PROT1_155871> to synergistically stimulate transcription ( CITATION , CITATION ) . The region involved in <PROT1_155871>  Tat </PROT1_155871> binding was mapped to amino acids corresponding to 247 - 282 in <PROT2_708>  p32 </PROT2_708> , which is outside the region where we see protection by Rev ( amino acids 196 - 208 ) . ||7778269_155871_708==>The <PROT2_708>  p32 </PROT2_708> protein has been shown to interact with human immunodeficiency virus ( HIV ) 1 <PROT1_155871>  Tat </PROT1_155871> protein ( CITATION - TARGET_CITATION ) and Rev protein ( CITATION , CITATION ) by using in vitro binding studies and two - hybrid analyses in yeast cells . ||8628270_1022_155871==>Many transcription activators , including HIV - 1 <PROT2_155871>  Tat </PROT2_155871> , herpes simplex virus VP16 , and human p53 and E2F1 , can bind TFIIH ( CITATION , TARGET_CITATION , CITATION ) whose <PROT1_1022>  CDK7 </PROT1_1022> subunit is a CTD kinase for RPII ( reviewed in refs. CITATION and CITATION ) . ||8628270_1022_155871==>The multi - subunit general transcription factor TFIIH , which has its own tripartite protein kinase , <PROT1_1022>  Cdk7 </PROT1_1022> & # x2013 ; cyclin H & # x2013 ; MAT1 , binds to the same domain of <PROT2_155871>  Tat </PROT2_155871> ( CITATION , CITATION , CITATION and TARGET_CITATION ) . ||8628270_1022_155871==>Transcription activators may remove hnRNP U and / or provide signals to inactivate hnRNP u. It remains to be determined whether a transcription factor such as <PROT2_155871>  Tat </PROT2_155871> , retinoic acid receptor alpha , p53 , or VP16 that binds TFIIH or <PROT1_1022>  Cdk7 </PROT1_1022> ( TARGET_CITATION , CITATION , CITATION , CITATION , CITATION , CITATION ) would affect the interaction of hnRNP U with TFIIH in vivo . ||8628270_1022_155871==>These proteins include the core RNA polymerase II ( CITATION , CITATION ) , whose C - terminal domain is required for <PROT2_155871>  Tat </PROT2_155871> - mediated transactivation ( CITATION ) , TAFII55 ( CITATION ) , and TFIIH and <PROT1_1022>  CDK7 </PROT1_1022> ( TARGET_CITATION , CITATION ) . ||8628270_1022_155871==><PROT2_155871>  Tat </PROT2_155871> , through its activation domain , interacts with the general transcription factor , TFIIH ( TARGET_CITATION ) , and stimulates the phosphorylation of the C - terminal domain of RNA polymerase II by its kinase component , <PROT1_1022>  cdk7 </PROT1_1022> ( CITATION , CITATION ) . ||8628270_155871_2966==><PROT1_155871>  Tat </PROT1_155871> was reported previously to bind to the p62 subunit of <PROT2_2966>  TFIIH </PROT2_2966> ( Blau et al. 1996 TARGET_CITATION ; Parada and Roeder 1996 CITATION ) . ||8628270_155871_2966==>HIV - 1 <PROT1_155871>  Tat </PROT1_155871> has previously been shown to associate with several components comprising the HIV - 1 preinitiation complex including SP1 ( CITATION ) , TATA - binding protein ( TBP ) and associated factors ( TAFs ) ( CITATION ) , the p62 subunit of <PROT2_2966>  TFIIH </PROT2_2966> ( TARGET_CITATION ) in addition to RNA polymerase II ( CITATION ) . ||8628270_155871_2966==>Many transcription activators , including HIV - 1 <PROT1_155871>  Tat </PROT1_155871> , herpes simplex virus VP16 , and human p53 and E2F1 , can bind <PROT2_2966>  TFIIH </PROT2_2966> ( CITATION , TARGET_CITATION , CITATION ) whose CDK7 subunit is a CTD kinase for RPII ( reviewed in refs. CITATION and CITATION ) . ||8628270_155871_2966==>The HIV - 1 <PROT1_155871>  Tat </PROT1_155871> protein stimulates elongation by RNAP II ( reviewed in ref. CITATION ) and interacts with two CTD kinases , <PROT2_2966>  TFIIH </PROT2_2966> ( TARGET_CITATION , CITATION , CITATION ) and P - TEFb ( CITATION , CITATION ) . ||8628270_155871_2966==>Although both <PROT1_155871>  Tat </PROT1_155871> and VP16 bind <PROT2_2966>  TFIIH </PROT2_2966> components ( TARGET_CITATION , CITATION and CITATION ) , <PROT1_155871>  Tat </PROT1_155871> but not VP16 stimulates the ability of kinases in <PROT2_2966>  TFIIH </PROT2_2966> to phosphorylate the RNA polymerase II CTD ( CITATION and CITATION ) . ||8628270_155871_2966==>The multi - subunit general transcription factor <PROT2_2966>  TFIIH </PROT2_2966> , which has its own tripartite protein kinase , Cdk7 & # x2013 ; cyclin H & # x2013 ; MAT1 , binds to the same domain of <PROT1_155871>  Tat </PROT1_155871> ( CITATION , CITATION , CITATION and TARGET_CITATION ) . ||8628270_155871_2966==>All of these factors , like <PROT1_155871>  Tat </PROT1_155871> , bind to <PROT2_2966>  TFIIH </PROT2_2966> ( TARGET_CITATION ) . ||8628270_155871_2966==>DRB may exert its effect by direct inhibition of a CTD kinase activity , and two DRB - sensitive cellular kinases , the CAK component of <PROT2_2966>  TFIIH </PROT2_2966> ( CITATION , TARGET_CITATION ) and <PROT1_155871>  Tat </PROT1_155871> - associated kinase ( TAK ) ( CITATION ) , have been found to interact with the activation domain of <PROT1_155871>  Tat </PROT1_155871> . ||8628270_155871_2966==>Transcription activators may remove hnRNP U and / or provide signals to inactivate hnRNP u. It remains to be determined whether a transcription factor such as <PROT1_155871>  Tat </PROT1_155871> , retinoic acid receptor alpha , p53 , or VP16 that binds <PROT2_2966>  TFIIH </PROT2_2966> or Cdk7 ( TARGET_CITATION , CITATION , CITATION , CITATION , CITATION , CITATION ) would affect the interaction of hnRNP U with <PROT2_2966>  TFIIH </PROT2_2966> in vivo . ||8628270_155871_2966==>In fact , <PROT1_155871>  Tat </PROT1_155871> has been shown to interact with <PROT2_2966>  TFIIH </PROT2_2966> and to stimulate phosphorylation of pol II CTD by the <PROT2_2966>  TFIIH </PROT2_2966> kinase , although different groups have different opinions on which subunit of <PROT2_2966>  TFIIH </PROT2_2966> mediates <PROT1_155871>  Tat </PROT1_155871> binding ( TARGET_CITATION , CITATION , CITATION , CITATION ) . ||8628270_155871_2966==>HIV - 1 <PROT1_155871>  Tat </PROT1_155871> has been shown to interact with <PROT2_2966>  TFIIH </PROT2_2966> ( TARGET_CITATION , CITATION , CITATION , CITATION ) and P - TEFb ( CITATION , CITATION ) in different reports following different protocols . ||8628270_155871_2966==>These proteins include the core RNA polymerase II ( CITATION , CITATION ) , whose C - terminal domain is required for <PROT1_155871>  Tat </PROT1_155871> - mediated transactivation ( CITATION ) , TAFII55 ( CITATION ) , and <PROT2_2966>  TFIIH </PROT2_2966> and CDK7 ( TARGET_CITATION , CITATION ) . ||8628270_155871_2966==>In addition to hCycT1 , a number of other potential <PROT1_155871>  Tat </PROT1_155871> interacting proteins and / or cofactors have been proposed including MSS1 , HT2A , CA150 , TFIID , <PROT1_155871>  Tat </PROT1_155871> - SF1 , TIP30 , and PolII itself ( CITATION ) , and other groups have reported interactions between <PROT1_155871>  Tat </PROT1_155871> and the coactivator proteins p300 and CREB - binding protein ( CBP ) ( CITATION ) or between <PROT1_155871>  Tat </PROT1_155871> and the transcription factor <PROT2_2966>  TFIIH </PROT2_2966> ( TARGET_CITATION , CITATION , CITATION , CITATION ) . ||8628270_155871_2966==>The reported interaction of <PROT1_155871>  Tat </PROT1_155871> with <PROT2_2966>  TFIIH </PROT2_2966> ( TARGET_CITATION , CITATION , CITATION , CITATION ) , which contains a CTD kinase activity , has led to the proposal that <PROT1_155871>  Tat </PROT1_155871> might activate the HIV - 1 LTR by the sequential TAR - independent recruitment of <PROT2_2966>  TFIIH </PROT2_2966> to LTR - bound PolII molecules , followed by the subsequent TAR - dependent recruitment of hCycT1 / P - TEFb ( CITATION , CITATION ) . ||8628270_155871_2966==><PROT2_2966>  TFIIH </PROT2_2966> has been found to associate with <PROT1_155871>  Tat </PROT1_155871> ( TARGET_CITATION , CITATION , CITATION , CITATION ) , and based on differential sensitivity of <PROT2_2966>  TFIIH </PROT2_2966> and P - TEFb to a pseudosubstrate peptide , it was concluded that in addition to P - TEFb , the kinase activity of <PROT2_2966>  TFIIH </PROT2_2966> was required for <PROT1_155871>  Tat </PROT1_155871> to work ( CITATION ) . ||8628270_155871_2966==><PROT1_155871>  Tat </PROT1_155871> , through its activation domain , interacts with the general transcription factor , <PROT2_2966>  TFIIH </PROT2_2966> ( TARGET_CITATION ) , and stimulates the phosphorylation of the C - terminal domain of RNA polymerase II by its kinase component , cdk7 ( CITATION , CITATION ) . ||8628270_155871_2966==>Many transcription activator proteins , including HSV VP16 and human p53 and Androgen Receptor , as well as HIV <PROT1_155871>  Tat </PROT1_155871> , bind to <PROT2_2966>  TFIIH </PROT2_2966> directly , which might stimulate its CTD kinase activity and facilitate entry into productive transcription elongation ( CITATION , CITATION , TARGET_CITATION and CITATION ) . ||8628270_155871_2966==>Perhaps not surprisingly , therefore , the activation domain of <PROT1_155871>  Tat </PROT1_155871> makes direct contact with the protein kinases <PROT2_2966>  TFIIH </PROT2_2966> , P - TEFb , TAFII250 and TIP30 and the protein phosphatase FCP1 ( CITATION , CITATION , CITATION , CITATION , CITATION and TARGET_CITATION ) . ||8628270_155871_2967==><PROT1_155871>  Tat </PROT1_155871> was reported previously to bind to the p62 subunit of <PROT2_2967>  TFIIH </PROT2_2967> ( Blau et al. 1996 TARGET_CITATION ; Parada and Roeder 1996 CITATION ) . ||8628270_155871_2967==>HIV - 1 <PROT1_155871>  Tat </PROT1_155871> has previously been shown to associate with several components comprising the HIV - 1 preinitiation complex including SP1 ( CITATION ) , TATA - binding protein ( TBP ) and associated factors ( TAFs ) ( CITATION ) , the p62 subunit of <PROT2_2967>  TFIIH </PROT2_2967> ( TARGET_CITATION ) in addition to RNA polymerase II ( CITATION ) . ||8628270_155871_2967==>Many transcription activators , including HIV - 1 <PROT1_155871>  Tat </PROT1_155871> , herpes simplex virus VP16 , and human p53 and E2F1 , can bind <PROT2_2967>  TFIIH </PROT2_2967> ( CITATION , TARGET_CITATION , CITATION ) whose CDK7 subunit is a CTD kinase for RPII ( reviewed in refs. CITATION and CITATION ) . ||8628270_155871_2967==>The HIV - 1 <PROT1_155871>  Tat </PROT1_155871> protein stimulates elongation by RNAP II ( reviewed in ref. CITATION ) and interacts with two CTD kinases , <PROT2_2967>  TFIIH </PROT2_2967> ( TARGET_CITATION , CITATION , CITATION ) and P - TEFb ( CITATION , CITATION ) . ||8628270_155871_2967==>Although both <PROT1_155871>  Tat </PROT1_155871> and VP16 bind <PROT2_2967>  TFIIH </PROT2_2967> components ( TARGET_CITATION , CITATION and CITATION ) , <PROT1_155871>  Tat </PROT1_155871> but not VP16 stimulates the ability of kinases in <PROT2_2967>  TFIIH </PROT2_2967> to phosphorylate the RNA polymerase II CTD ( CITATION and CITATION ) . ||8628270_155871_2967==>The multi - subunit general transcription factor <PROT2_2967>  TFIIH </PROT2_2967> , which has its own tripartite protein kinase , Cdk7 & # x2013 ; cyclin H & # x2013 ; MAT1 , binds to the same domain of <PROT1_155871>  Tat </PROT1_155871> ( CITATION , CITATION , CITATION and TARGET_CITATION ) . ||8628270_155871_2967==>All of these factors , like <PROT1_155871>  Tat </PROT1_155871> , bind to <PROT2_2967>  TFIIH </PROT2_2967> ( TARGET_CITATION ) . ||8628270_155871_2967==>DRB may exert its effect by direct inhibition of a CTD kinase activity , and two DRB - sensitive cellular kinases , the CAK component of <PROT2_2967>  TFIIH </PROT2_2967> ( CITATION , TARGET_CITATION ) and <PROT1_155871>  Tat </PROT1_155871> - associated kinase ( TAK ) ( CITATION ) , have been found to interact with the activation domain of <PROT1_155871>  Tat </PROT1_155871> . ||8628270_155871_2967==>Transcription activators may remove hnRNP U and / or provide signals to inactivate hnRNP u. It remains to be determined whether a transcription factor such as <PROT1_155871>  Tat </PROT1_155871> , retinoic acid receptor alpha , p53 , or VP16 that binds <PROT2_2967>  TFIIH </PROT2_2967> or Cdk7 ( TARGET_CITATION , CITATION , CITATION , CITATION , CITATION , CITATION ) would affect the interaction of hnRNP U with <PROT2_2967>  TFIIH </PROT2_2967> in vivo . ||8628270_155871_2967==>In fact , <PROT1_155871>  Tat </PROT1_155871> has been shown to interact with <PROT2_2967>  TFIIH </PROT2_2967> and to stimulate phosphorylation of pol II CTD by the <PROT2_2967>  TFIIH </PROT2_2967> kinase , although different groups have different opinions on which subunit of <PROT2_2967>  TFIIH </PROT2_2967> mediates <PROT1_155871>  Tat </PROT1_155871> binding ( TARGET_CITATION , CITATION , CITATION , CITATION ) . ||8628270_155871_2967==>HIV - 1 <PROT1_155871>  Tat </PROT1_155871> has been shown to interact with <PROT2_2967>  TFIIH </PROT2_2967> ( TARGET_CITATION , CITATION , CITATION , CITATION ) and P - TEFb ( CITATION , CITATION ) in different reports following different protocols . ||8628270_155871_2967==>These proteins include the core RNA polymerase II ( CITATION , CITATION ) , whose C - terminal domain is required for <PROT1_155871>  Tat </PROT1_155871> - mediated transactivation ( CITATION ) , TAFII55 ( CITATION ) , and <PROT2_2967>  TFIIH </PROT2_2967> and CDK7 ( TARGET_CITATION , CITATION ) . ||8628270_155871_2967==>In addition to hCycT1 , a number of other potential <PROT1_155871>  Tat </PROT1_155871> interacting proteins and / or cofactors have been proposed including MSS1 , HT2A , CA150 , TFIID , <PROT1_155871>  Tat </PROT1_155871> - SF1 , TIP30 , and PolII itself ( CITATION ) , and other groups have reported interactions between <PROT1_155871>  Tat </PROT1_155871> and the coactivator proteins p300 and CREB - binding protein ( CBP ) ( CITATION ) or between <PROT1_155871>  Tat </PROT1_155871> and the transcription factor <PROT2_2967>  TFIIH </PROT2_2967> ( TARGET_CITATION , CITATION , CITATION , CITATION ) . ||8628270_155871_2967==>The reported interaction of <PROT1_155871>  Tat </PROT1_155871> with <PROT2_2967>  TFIIH </PROT2_2967> ( TARGET_CITATION , CITATION , CITATION , CITATION ) , which contains a CTD kinase activity , has led to the proposal that <PROT1_155871>  Tat </PROT1_155871> might activate the HIV - 1 LTR by the sequential TAR - independent recruitment of <PROT2_2967>  TFIIH </PROT2_2967> to LTR - bound PolII molecules , followed by the subsequent TAR - dependent recruitment of hCycT1 / P - TEFb ( CITATION , CITATION ) . ||8628270_155871_2967==><PROT2_2967>  TFIIH </PROT2_2967> has been found to associate with <PROT1_155871>  Tat </PROT1_155871> ( TARGET_CITATION , CITATION , CITATION , CITATION ) , and based on differential sensitivity of <PROT2_2967>  TFIIH </PROT2_2967> and P - TEFb to a pseudosubstrate peptide , it was concluded that in addition to P - TEFb , the kinase activity of <PROT2_2967>  TFIIH </PROT2_2967> was required for <PROT1_155871>  Tat </PROT1_155871> to work ( CITATION ) . ||8628270_155871_2967==><PROT1_155871>  Tat </PROT1_155871> , through its activation domain , interacts with the general transcription factor , <PROT2_2967>  TFIIH </PROT2_2967> ( TARGET_CITATION ) , and stimulates the phosphorylation of the C - terminal domain of RNA polymerase II by its kinase component , cdk7 ( CITATION , CITATION ) . ||8628270_155871_2967==>Many transcription activator proteins , including HSV VP16 and human p53 and Androgen Receptor , as well as HIV <PROT1_155871>  Tat </PROT1_155871> , bind to <PROT2_2967>  TFIIH </PROT2_2967> directly , which might stimulate its CTD kinase activity and facilitate entry into productive transcription elongation ( CITATION , CITATION , TARGET_CITATION and CITATION ) . ||8628270_155871_2967==>Perhaps not surprisingly , therefore , the activation domain of <PROT1_155871>  Tat </PROT1_155871> makes direct contact with the protein kinases <PROT2_2967>  TFIIH </PROT2_2967> , P - TEFb , TAFII250 and TIP30 and the protein phosphatase FCP1 ( CITATION , CITATION , CITATION , CITATION , CITATION and TARGET_CITATION ) . ||8628270_155871_2968==><PROT1_155871>  Tat </PROT1_155871> was reported previously to bind to the p62 subunit of <PROT2_2968>  TFIIH </PROT2_2968> ( Blau et al. 1996 TARGET_CITATION ; Parada and Roeder 1996 CITATION ) . ||8628270_155871_2968==>HIV - 1 <PROT1_155871>  Tat </PROT1_155871> has previously been shown to associate with several components comprising the HIV - 1 preinitiation complex including SP1 ( CITATION ) , TATA - binding protein ( TBP ) and associated factors ( TAFs ) ( CITATION ) , the p62 subunit of <PROT2_2968>  TFIIH </PROT2_2968> ( TARGET_CITATION ) in addition to RNA polymerase II ( CITATION ) . ||8628270_155871_2968==>Many transcription activators , including HIV - 1 <PROT1_155871>  Tat </PROT1_155871> , herpes simplex virus VP16 , and human p53 and E2F1 , can bind <PROT2_2968>  TFIIH </PROT2_2968> ( CITATION , TARGET_CITATION , CITATION ) whose CDK7 subunit is a CTD kinase for RPII ( reviewed in refs. CITATION and CITATION ) . ||8628270_155871_2968==>The HIV - 1 <PROT1_155871>  Tat </PROT1_155871> protein stimulates elongation by RNAP II ( reviewed in ref. CITATION ) and interacts with two CTD kinases , <PROT2_2968>  TFIIH </PROT2_2968> ( TARGET_CITATION , CITATION , CITATION ) and P - TEFb ( CITATION , CITATION ) . ||8628270_155871_2968==>Although both <PROT1_155871>  Tat </PROT1_155871> and VP16 bind <PROT2_2968>  TFIIH </PROT2_2968> components ( TARGET_CITATION , CITATION and CITATION ) , <PROT1_155871>  Tat </PROT1_155871> but not VP16 stimulates the ability of kinases in <PROT2_2968>  TFIIH </PROT2_2968> to phosphorylate the RNA polymerase II CTD ( CITATION and CITATION ) . ||8628270_155871_2968==>The multi - subunit general transcription factor <PROT2_2968>  TFIIH </PROT2_2968> , which has its own tripartite protein kinase , Cdk7 & # x2013 ; cyclin H & # x2013 ; MAT1 , binds to the same domain of <PROT1_155871>  Tat </PROT1_155871> ( CITATION , CITATION , CITATION and TARGET_CITATION ) . ||8628270_155871_2968==>All of these factors , like <PROT1_155871>  Tat </PROT1_155871> , bind to <PROT2_2968>  TFIIH </PROT2_2968> ( TARGET_CITATION ) . ||8628270_155871_2968==>DRB may exert its effect by direct inhibition of a CTD kinase activity , and two DRB - sensitive cellular kinases , the CAK component of <PROT2_2968>  TFIIH </PROT2_2968> ( CITATION , TARGET_CITATION ) and <PROT1_155871>  Tat </PROT1_155871> - associated kinase ( TAK ) ( CITATION ) , have been found to interact with the activation domain of <PROT1_155871>  Tat </PROT1_155871> . ||8628270_155871_2968==>Transcription activators may remove hnRNP U and / or provide signals to inactivate hnRNP u. It remains to be determined whether a transcription factor such as <PROT1_155871>  Tat </PROT1_155871> , retinoic acid receptor alpha , p53 , or VP16 that binds <PROT2_2968>  TFIIH </PROT2_2968> or Cdk7 ( TARGET_CITATION , CITATION , CITATION , CITATION , CITATION , CITATION ) would affect the interaction of hnRNP U with <PROT2_2968>  TFIIH </PROT2_2968> in vivo . ||8628270_155871_2968==>In fact , <PROT1_155871>  Tat </PROT1_155871> has been shown to interact with <PROT2_2968>  TFIIH </PROT2_2968> and to stimulate phosphorylation of pol II CTD by the <PROT2_2968>  TFIIH </PROT2_2968> kinase , although different groups have different opinions on which subunit of <PROT2_2968>  TFIIH </PROT2_2968> mediates <PROT1_155871>  Tat </PROT1_155871> binding ( TARGET_CITATION , CITATION , CITATION , CITATION ) . ||8628270_155871_2968==>HIV - 1 <PROT1_155871>  Tat </PROT1_155871> has been shown to interact with <PROT2_2968>  TFIIH </PROT2_2968> ( TARGET_CITATION , CITATION , CITATION , CITATION ) and P - TEFb ( CITATION , CITATION ) in different reports following different protocols . ||8628270_155871_2968==>These proteins include the core RNA polymerase II ( CITATION , CITATION ) , whose C - terminal domain is required for <PROT1_155871>  Tat </PROT1_155871> - mediated transactivation ( CITATION ) , TAFII55 ( CITATION ) , and <PROT2_2968>  TFIIH </PROT2_2968> and CDK7 ( TARGET_CITATION , CITATION ) . ||8628270_155871_2968==>In addition to hCycT1 , a number of other potential <PROT1_155871>  Tat </PROT1_155871> interacting proteins and / or cofactors have been proposed including MSS1 , HT2A , CA150 , TFIID , <PROT1_155871>  Tat </PROT1_155871> - SF1 , TIP30 , and PolII itself ( CITATION ) , and other groups have reported interactions between <PROT1_155871>  Tat </PROT1_155871> and the coactivator proteins p300 and CREB - binding protein ( CBP ) ( CITATION ) or between <PROT1_155871>  Tat </PROT1_155871> and the transcription factor <PROT2_2968>  TFIIH </PROT2_2968> ( TARGET_CITATION , CITATION , CITATION , CITATION ) . ||8628270_155871_2968==>The reported interaction of <PROT1_155871>  Tat </PROT1_155871> with <PROT2_2968>  TFIIH </PROT2_2968> ( TARGET_CITATION , CITATION , CITATION , CITATION ) , which contains a CTD kinase activity , has led to the proposal that <PROT1_155871>  Tat </PROT1_155871> might activate the HIV - 1 LTR by the sequential TAR - independent recruitment of <PROT2_2968>  TFIIH </PROT2_2968> to LTR - bound PolII molecules , followed by the subsequent TAR - dependent recruitment of hCycT1 / P - TEFb ( CITATION , CITATION ) . ||8628270_155871_2968==><PROT2_2968>  TFIIH </PROT2_2968> has been found to associate with <PROT1_155871>  Tat </PROT1_155871> ( TARGET_CITATION , CITATION , CITATION , CITATION ) , and based on differential sensitivity of <PROT2_2968>  TFIIH </PROT2_2968> and P - TEFb to a pseudosubstrate peptide , it was concluded that in addition to P - TEFb , the kinase activity of <PROT2_2968>  TFIIH </PROT2_2968> was required for <PROT1_155871>  Tat </PROT1_155871> to work ( CITATION ) . ||8628270_155871_2968==><PROT1_155871>  Tat </PROT1_155871> , through its activation domain , interacts with the general transcription factor , <PROT2_2968>  TFIIH </PROT2_2968> ( TARGET_CITATION ) , and stimulates the phosphorylation of the C - terminal domain of RNA polymerase II by its kinase component , cdk7 ( CITATION , CITATION ) . ||8628270_155871_2968==>Many transcription activator proteins , including HSV VP16 and human p53 and Androgen Receptor , as well as HIV <PROT1_155871>  Tat </PROT1_155871> , bind to <PROT2_2968>  TFIIH </PROT2_2968> directly , which might stimulate its CTD kinase activity and facilitate entry into productive transcription elongation ( CITATION , CITATION , TARGET_CITATION and CITATION ) . ||8628270_155871_2968==>Perhaps not surprisingly , therefore , the activation domain of <PROT1_155871>  Tat </PROT1_155871> makes direct contact with the protein kinases <PROT2_2968>  TFIIH </PROT2_2968> , P - TEFb , TAFII250 and TIP30 and the protein phosphatase FCP1 ( CITATION , CITATION , CITATION , CITATION , CITATION and TARGET_CITATION ) . ||8628270_155871_902==>DRB may exert its effect by direct inhibition of a CTD kinase activity , and two DRB - sensitive cellular kinases , the <PROT2_902>  CAK </PROT2_902> component of TFIIH ( CITATION , TARGET_CITATION ) and <PROT1_155871>  Tat </PROT1_155871> - associated kinase ( TAK ) ( CITATION ) , have been found to interact with the activation domain of <PROT1_155871>  Tat