HIV-1 Tat acts as a processivity factor in vitro in conjunction with cellular elongation factors.

Kato, Hiroyuki; Sumimoto, Hideki; Pognonec, Philippe; Chen, Chein Hwa; Rosen, Craig A.; Roeder, Robert G.

doi:10.1101/gad.6.4.655

Cited by 190 publications

(128 citation statements)

References 66 publications

(71 reference statements)

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“…One could therefore explain part of the synergism in transcriptional activation if interaction of acidic activators with TFIIH stimulates melting of the DNA at the promoter. This phenomenon would have been difficult to detect in vitro because acidic activators also stimulate formation of the closed preinitiation complex (65,112,114 18) and increasing the processivity of chain elongation by RNA polymerase 11 (52,54,61,71). Similarly, other typical activators, including VP16, may also generally stimulate chain elongation by RNA polymerase 11 (119).…”

Section: Discussionmentioning

confidence: 99%

Binding of basal transcription factor TFIIH to the acidic activation domains of VP16 and p53.

Xiao¹,

Pearson²,

Coulombe³

et al. 1994

Mol. Cell. Biol.

339

274

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Acidic transcriptional activation domains function well in both yeast and mammalian cells, and some have been shown to bind the general transcription factors TFIID and TFIIB. We now show that two acidic transactivators, herpes simplex virus VP16 and human p53, directly interact with the multisubunit human general transcription factor TFIHH and its Saccharomyces cerevisuze counterpart, factor b. The VP16-and p53-binding domains in these factors lie in the p62 subunit of TFIIH and in the homologous subunit, TFB1, of factor b. Point mutations in VP16 that reduce its transactivation activity in both yeast and mammalian cells weaken its binding to both yeast and human TFIIH. This suggests that binding of activation domains to TFIIH is an important aspect of transcriptional activation.Accurate transcription in vitro by human RNA polymerase II involves the general transcription factors TFIIA, TFIIB, TFIID, TFIIE, TFIIF (RAP30 and RAP74), TFIIH (also known as BTF2), and TFIIJ (reviewed in references 13 and 121). Beginning with TFIID, which recognizes the TATA boxes present in many promoters for RNA polymerase II, these factors and RNA polymerase II can be assembled in a defined order onto a promoter (5). TFIIH and TFIIJ are the last of these factors to bind to an assembling initiation complex (12,14,26), and TFIIH, also known as BTF2, is the only factor known to possess associated enzymatic activities. These include an ATP-dependent DNA helicase activity (95, 96) and a protein kinase activity that can phosphorylate the carboxyterminal heptapeptide repeat domain (CTD) of the largest subunit of RNA polymerase 11 (12, 21,68 herpes simplex virus transactivator VP16 (107) and in the N-terminal 73 amino acids of the mammalian tumor suppressor protein p53 (23). The p53 protein has a site-specific DNA-binding domain in its carboxy-terminal portion (101). VP16 does not, by itself, bind specifically to DNA, but instead its amino-terminal portion binds DNA in association with mammalian factors, including the POU homeodomain protein Oct-1 that recognizes octamer sequences in DNA (28,60,102). When fused to the DNA-binding domain of GAL4, the VP16 and p53 activation domains stimulate transcription in yeast and human cells of a gene bearing GAL4-binding sites (9,16,23,74,87,92). These observations imply that common mechanisms for transcriptional activation by acidic activators may exist in fungi and mammals.Many activation domains have been shown to interact with the TATA-box-binding protein (TBP) subunit of TFIID. These include the highly acidic activation domains in VP16 (50,103), p53 (10,67,72,84,97,108),118), and E2F-1 (37), as well as other kinds of activation domains found in the adenovirus activator ElA (48, 62), the Epstein-Barr virus proteins Zta (64) and R (70), the human T-cell leukemia virus type 1 (HTLV-1) activator Taxl (8), the transactivator Tat of human immunodeficiency virus type 1 (HIV-1) (53), and human c-Fos and c-Jun (85), PU-1 (38), and Spl (20). In certain cases, reduced binding of TBP by activation domains wit...

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Section: Discussionmentioning

confidence: 99%

Binding of basal transcription factor TFIIH to the acidic activation domains of VP16 and p53.

Xiao¹,

Pearson²,

Coulombe³

et al. 1994

Mol. Cell. Biol.

339

274

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“…Antitermination by the N protein involves the host proteins, NusA, NusB, NusG, ribosomal protein S10 and RNA elements at the 5Ј end of nascent viral transcripts. Whereas processive mechanisms found in phage have been extensively characterized and references therein), the mechanisms in eukaryotes are much less understood, except for the Drosophila hsp70 gene (Rougvie and Lis 1988;O'Brien and Lis 1991), the c-myc gene (Krumm et al 1992;Strobl and Eick 1992), and factor TFIIF (Price et al 1989;Bengal et al 1991), TFIIS (Sekimizu et al 1976), SIII (Elongin) (Bradsher et al 1993a,b;Aso et al 1995), P-TEFb (Marshall andPrice 1995;Marshall et al 1996), and HIV-1 Tat (Marciniak and Sharp 1991;Kato et al 1992;Zhou and Sharp 1995;Mancebo et al 1997;Zhu et al 1997). Tat activation of HIV-1 transcription is interesting because Tat enhances the processivity of transcription complexes in a manner reminiscent of N , and Tat activation is sensitive to DRB (Marciniak and Sharp 1991;Zhou and Sharp 1995;Mancebo et al 1997;Zhu et al 1997).…”

Section: Antitermination Mechanisms In Eukaryotesmentioning

confidence: 99%

DSIF, a novel transcription elongation factor that regulates RNA polymerase II processivity, is composed of human Spt4 and Spt5 homologs

Wada

Takagi

Yamaguchi

et al. 1998

Genes & Development

659

707

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We report the identification of a transcription elongation factor from HeLa cell nuclear extracts that causes pausing of RNA polymerase II (Pol II) in conjunction with the transcription inhibitor 5,6-dichloro-1-␤-D-ribofuranosylbenzimidazole (DRB). This factor, termed DRB sensitivity-inducing factor (DSIF), is also required for transcription inhibition by H8. DSIF has been purified and is composed of 160-kD (p160) and 14-kD (p14) subunits. Isolation of a cDNA encoding DSIF p160 shows it to be a homolog of the Saccharomyces cerevisiae transcription factor Spt5. Recombinant Supt4h protein, the human homolog of yeast Spt4, is functionally equivalent to DSIF p14, indicating that DSIF is composed of the human homologs of Spt4 and Spt5. In addition to its negative role in elongation, DSIF is able to stimulate the rate of elongation by RNA Pol II in a reaction containing limiting concentrations of ribonucleoside triphosphates. A role for DSIF in transcription elongation is further supported by the fact that p160 has a region homologous to the bacterial elongation factor NusG. The combination of biochemical studies on DSIF and genetic analysis of Spt4 and Spt5 in yeast, also in this issue, indicates that DSIF associates with RNA Pol II and regulates its processivity in vitro and in vivo.

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“…Tat is able to stimulate elongation, in some cases without any apparent effect on initiation (31,33,40,47), whereas VP16 also strongly stimulates initiation. Tat is a unique activator because it is recruited to the transcription complex by binding to nascent RNA rather than to promoter DNA.…”

mentioning

confidence: 99%

Three Functional Classes of Transcriptional Activation Domains

Blau

Xiao

McCracken

et al. 1996

Molecular and Cellular Biology

257

263

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We have studied the abilities of different transactivation domains to stimulate the initiation and elongation (postinitiation) steps of RNA polymerase II transcription in vivo. Nuclear run-on and RNase protection analyses revealed three classes of activation domains: Sp1 and CTF stimulated initiation (type I); human immunodeficiency virus type 1 Tat fused to a DNA binding domain stimulated predominantly elongation (type IIA); and VP16, p53, and E2F1 stimulated both initiation and elongation (type IIB). A quadruple point mutation of VP16 converted it from a type IIB to a type I activator. Type I and type IIA activators synergized with one another but not with type IIB activators. This observation implies that synergy can result from the concerted action of factors stimulating two different steps in transcription: initiation and elongation. The functional differences between activators may be explained by the different contacts they make with general transcription factors. In support of this idea, we found a correlation between the abilities of activators, including Tat, to stimulate elongation and their abilities to bind TFIIH.Stimulation of eukaryotic gene expression requires sequence-specific factors with DNA binding domains and activation domains that interact with the general transcription factors (GTFs) and recruit RNA polymerase II (pol II) to the promoter (3, 65). In vivo the transcriptionally active form of pol II is probably a holoenzyme complex which contains a number of the GTFs as well as other polypeptides (36). Different activation domains interact with different GTFs, including TFIIB (44), TFIID (17,19,63), and TFIIF (76). These interactions are thought to recruit, stabilize, and/or modify the activity of the pol II holoenzyme.We recently demonstrated that the activation domains of p53, VP16, and E2F1 bind directly to TFIIH (50a, 72). TFIIH is a multisubunit factor, different forms of which are required for both transcription and nucleotide excision repair of DNA (9). TFIIH is the only GTF which has enzymatic activities: it has two helicase subunits and a cyclin-dependent protein kinase subunit which phosphorylates the pol II large-subunit C-terminal domain (CTD) (12,52,58,60). Both of these enzymatic activities are implicated in steps in transcription which occur shortly after initiation of the RNA chain. First, a helicase is required for efficient formation of open complexes and for promoter clearance on linear templates in vitro (20). Second, when paused polymerases resume elongation on several Drosophila genes in vivo, the CTD becomes phosphorylated, suggesting a possible role for TFIIH kinase in regulating elongation (50, 70). Furthermore, inhibitors of the TFIIH kinase inhibit elongation under activated (74), but not basal (57), transcription conditions.In vivo, rate-limiting steps after initiation have been well documented for a number of genes. For example, polymerases stall 20 to 40 bases downstream of the start sites in the Drosophila hsp70 and human c-myc genes (38, 51, 64) and terminate...

show abstract

HIV-1 Tat acts as a processivity factor in vitro in conjunction with cellular elongation factors.

Cited by 190 publications

References 66 publications

Binding of basal transcription factor TFIIH to the acidic activation domains of VP16 and p53.

Binding of basal transcription factor TFIIH to the acidic activation domains of VP16 and p53.

DSIF, a novel transcription elongation factor that regulates RNA polymerase II processivity, is composed of human Spt4 and Spt5 homologs

Three Functional Classes of Transcriptional Activation Domains

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