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Query: UNIPROT:P23193 (transcription elongation factor)
 739 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Previous characterization of the Saccharomyces cerevisiae Spt4, Spt5, and Spt6 proteins suggested that these proteins act as transcription factors that modify chromatin structure. In this work, we report new genetic and biochemical studies of Spt4, Spt5, and Spt6 that reveal a role for these factors in transcription elongation. We have isolated conditional mutations in SPT5 that can be suppressed in an allele-specific manner by mutations in the two largest subunits of RNA polymerase II (Pol II). Strikingly, one of these RNA Pol II mutants is defective for transcription elongation and the others cause phenotypes consistent with an elongation defect. In addition, we show that spt4, spt5, and spt6 mutants themselves have phenotypes suggesting defects in transcription elongation in vivo. Consistent with these findings, we show that Spt5 is physically associated with RNA Pol II in vivo, and have identified a region of sequence similarity between Spt5 and NusG, an Escherichia coli transcription elongation factor that binds directly to RNA polymerase. Finally, we show that Spt4 and Spt5 are tightly associated in a complex that does not contain Spt6. These results, taken together with the biochemical identification of a human Spt4-Spt5 complex as a transcription elongation factor (Wada et al. 1998), provide strong evidence that these factors are important for transcription elongation in vivo.
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PMID:Evidence that Spt4, Spt5, and Spt6 control transcription elongation by RNA polymerase II in Saccharomyces cerevisiae. 945 Sep 30

The HIV-1 Tat protein regulates transcription elongation through binding to the viral TAR RNA stem-loop structure. We have isolated a novel 87 kDa cyclin C-related protein (cyclin T) that interacts specifically with the transactivation domain of Tat. Cyclin T is a partner for CDK9, an RNAPII transcription elongation factor. Remarkably, the interaction of Tat with cyclin T strongly enhances the affinity and specificity of the Tat:TAR RNA interaction, and confers a requirement for sequences in the loop of TAR that are not recognized by Tat alone. Moreover, overexpression of human cyclin T rescues Tat activity in nonpermissive rodent cells. We propose that Tat directs cyclin T-CDK9 to RNAPII through cooperative binding to TAR RNA.
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PMID:A novel CDK9-associated C-type cyclin interacts directly with HIV-1 Tat and mediates its high-affinity, loop-specific binding to TAR RNA. 949 87

The transition from abortive into productive elongation is proposed to be controlled by a positive transcription elongation factor b (P-TEFb) through phosphorylation of the carboxy-terminal domain (CTD) of the largest subunit of RNA polymerase II. Drosophila P-TEFb was identified recently as a cyclin-dependent kinase (CDK9) paired with a cyclin subunit (cyclin T). We demonstrate here the cloning of multiple cyclin subunits of human P-TEFb (T1 and T2). Cyclin T2 has two forms (T2a and T2b) because of alternative splicing. Both cyclin T1 and T2 are ubiquitously expressed. Immunoprecipitation and immunodepletion experiments carried out on HeLa nuclear extract (HNE) indicated that cyclin T1 and T2 were associated with CDK9 in a mutually exclusive manner and that almost all CDK9 was associated with either cyclin T1 or T2. Recombinant CDK9/cyclin T1, CDK9/cyclin T2a, and CDK9/cyclin T2b produced in Sf9 cells possessed DRB-sensitive kinase activity and functioned in transcription elongation in vitro. Either cyclin T1 or T2 was required to activate CDK9, and the truncation of the carboxyl terminus of the cyclin reduced, but did not eliminate, P-TEFb activity. Cotransfection experiments indicated that all three CDK9/cyclin combinations dramatically activated the CMV promoter.
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PMID:Identification of multiple cyclin subunits of human P-TEFb. 949 9

Mutations that increase the low-level transcription of the Saccharomyces cerevisiae HIS4 gene, which results from deletion of the genes encoding transcription factors BAS1, BAS2, and GCN4, were isolated previously in SIT1 (also known as RPO21, RPB1, and SUA8), the gene encoding the largest subunit of RNA polymerase II (RNAPII). Here we show that sit1 substitutions cluster in two conserved regions of the enzyme which form part of the active site. Six sit1 mutations, affect region F, a region that is involved in transcriptional elongation and in resistance to alpha-aminatin. Four sit1 substitutions lie in another region involved in transcriptional elongation, region D, which binds Mg2+ ions essential for RNA catalysis. One region D substitution is lethal unless suppressed by a substitution in region G and interacts genetically with PPR2, the gene encoding transcription elongation factor IIS. Some sit1 substitutions affect the selection of transcriptional start sites at the CYC1 promoter in a manner reminiscent of that of sua8 (sua stands for suppression of upstream ATG) mutations. Together with previous findings which indicate that regions D and G are in close proximity to the 3' end of the nascent transcript and that region F is involved in the translocation process, our results suggest that transcriptional activation by the sit1 mutations results from alteration of the RNAPII active center.
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PMID:Stimulation of transcription by mutations affecting conserved regions of RNA polymerase II. 957 41

DRB is a classic inhibitor of transcription by RNA polymerase II (pol II). Although it has been demonstrated that DRB inhibits the elongation step of transcription, its mode of action has been elusive. DRB also markedly inhibits human immunodeficiency virus (HIV) transcription, by targeting the elongation which is enhanced by the HIV-encoded transactivator Tat. Two factors essential for DRB action have recently been identified. These factors, positive transcription elongation factor b (P-TEFb) and DRB sensitivity-inducing factor (DSIF), positively and negatively regulate pol II elongation, and are likely to be relevant to the function of Tat. In this review, we summarize the recent findings on these factors, and discuss a possible model for the molecular mechanism of DRB action.
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PMID:Interplay between positive and negative elongation factors: drawing a new view of DRB. 958 78

We developed a system to identify the viral proteins required for the packaging and passage of human respiratory syncytial virus (RSV) by reconstructing these events with cDNA-encoded components. Plasmids encoding individual RSV proteins, each under the control of a T7 promoter, were cotransfected in various combinations together with a plasmid containing a minigenome into cells infected with a vaccinia virus recombinant expressing T7 RNA polymerase. Supernatants from these cells were passaged onto fresh cells which were then superinfected with RSV. Functional reconstitution of RSV-specific packaging and passage was detected by expression of the reporter gene carried on the minigenome. As expected, the four nucleocapsid proteins N, P, L, and M2-1 failed to direct packaging and passage of the minigenome. Passage was achieved by further addition of plasmids expressing three membrane-associated proteins, M, G, and F; inclusion of the fourth envelope- associated protein, SH, did not alter passage efficiency. Passage was reduced 10- to 20-fold by omission of G and was abrogated by omission of either M or F. Coexpression of the nonstructural NS1 or NS2 protein had little effect on packaging and passage except through indirect effects on RNA synthesis in the initial transfection. The M2-1 transcription elongation factor was not required for the generation of passage-competent particles. However, addition of increasing quantities of M2-1 to the transfection mediated a dose-dependent inhibition of passage which was alleviated by coexpression of the putative negative regulatory factor M2-2. Omission of the L plasmid reduced passage 10- to 20-fold, most likely due to reduced availability of encapsidated minigenomes for packaging. However, the residual level of passage indicated that neither L protein nor the process of RSV-specific RNA synthesis is required for the production and passage of particles. Omission of N or P from the transfection abrogated passage. Thus, the minimum RSV protein requirements for packaging and passaging a minigenome are N, P, M, and F, although the efficiency is greatly increased by addition of L and G.
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PMID:Identification of the respiratory syncytial virus proteins required for formation and passage of helper-dependent infectious particles. 962 Oct 29

Prior genetic analysis suggests that there may exist an interaction between the products of the vaccinia virus genes A18R, a putative negative transcription elongation factor, and G2R, a putative positive transcription elongation factor. In addition, affinity purification of polyhistidine-tagged G2R protein overexpressed in vaccinia virus-infected cells, reported here, results in copurification of the vaccinia H5R protein, previously characterized as a late viral transcription factor. We have therefore used several methods to screen further for interactions among the G2R, A18R, and H5R proteins. Methods include copurification or co-immunoprecipitation of proteins overexpressed during vaccinia virus infection, activation of the gal 4 promoter by gal 4 fusions in the yeast two-hybrid system, and co-immunoprecipitation of proteins synthesized in vitro in a rabbit reticulocyte lysate. The results reveal interactions which include all possible pairwise combinations of the three proteins G2R, A18R, and H5R; however, not all possible permutations of the interactions are observed and the interactions are not observed in all environments tested. The results suggest that the vaccinia virus proteins G2R, A18R, and H5R interact as part of a higher order transcription complex.
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PMID:Characterization of the interactions among vaccinia virus transcription factors G2R, A18R, and H5R. 963 70

Tat stimulates human immunodeficiency virus type 1 (HIV-1) transcription elongation through recognition of the transactivation response (TAR) RNA stem-loop structure at the 5' end of nascent viral transcripts. Recently, a human transcription elongation factor P-TEFb, consisting of CDK9 kinase, cyclin T and other associated factors, has been shown to interact with Tat to restore Tat activation in HeLa nuclear extract depleted of P-TEFb. Here, we report the purification of a P-TEFb complex fraction containing epitope-tagged wild-type CDK9 or kinase-inactive CDK9 and five tightly associated polypeptides. Only wild-type P-TEFb complex with an active CDK9 kinase was able to hyperphosphorylate the C-terminal domain of RNA polymerase II and mediate Tat transactivation in P-TEFb-depleted HeLa nuclear extract. Tat also stimulated transcription elongation by recruitment of the P-TEFb complex to the HIV-1 promoter through a Tat-TAR interaction. A possible mechanism for P-TEFb to become associated with polymerase elongation complexes and function as a general elongation factor was demonstrated by an interaction of P-TEFb with double-stranded RNA molecules through an 87 kDa subunit. Finally, P-TEFb was found to interact with and phosphorylate Tat-SF1, a Tat cofactor required for Tat transactivation. Our data indicate that the various subunits of the human P-TEFb complex may play distinct roles at multiple stages to mediate Tat activation of HIV-1 transcription elongation.
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PMID:Transcription elongation factor P-TEFb mediates Tat activation of HIV-1 transcription at multiple stages. 964 38

Loss of vaccinia virus A18R gene function results in an aberrant transcription profile termed promiscuous transcription, defined as transcription within regions of the genome which are normally transcriptionally silent late during infection. Promiscuous transcription results in an increase in the intracellular concentration of double-stranded RNA, which in turn results in activation of the cellular 2-5A pathway and subsequent RNase L-catalyzed degradation of viral and cellular RNAs. One of three hypotheses could account for promiscuous transcription: (i) reactivation of early promoters late during infection, (ii) random transcription initiation, (iii) readthrough transcription from upstream promoters. Transcriptional analysis of several viral genes, presented here, argues strongly against the first two hypotheses. We have tested the readthrough hypothesis by conducting a detailed transcriptional analysis of a region of the vaccinia virus genome which contains three early genes (M1L, M2L, and K1L) positioned directly downstream of the intermediate gene, K2L. The results show that mutation of the A18R gene results in increased readthrough transcription of the M1L gene originating from the K2L intermediate promoter. A18R mutant infection of RNase L knockout mouse fibroblast (KO3) cells does not result in 2-5A pathway activation, yet the virus mutant is defective in late viral gene expression and remains temperature sensitive. These results demonstrate that the A18R gene product is a negative transcription elongation factor for postreplicative viral genes.
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PMID:The vaccinia virus A18R DNA helicase is a postreplicative negative transcription elongation factor. 969 93

By binding to the transactivation response element (TAR) RNA, the transcriptional transactivator (Tat) from the human immunodeficiency virus increases rates of elongation rather than initiation of viral transcription. Two cyclin-dependent serine/threonine kinases, CDK7 and CDK9, which phosphorylate the C-terminal domain of RNA polymerase II, have been implicated in Tat transactivation in vivo and in vitro. In this report, we demonstrate that CDK9, which is the kinase component of the positive transcription elongation factor b (P-TEFb) complex, can activate viral transcription when tethered to the heterologous Rev response element RNA via the regulator of expression of virion proteins (Rev). The kinase activity of CDK9 and cyclin T1 is essential for these effects. Moreover, P-TEFb binds to TAR only in the presence of Tat. We conclude that Tat-P-TEFb complexes bind to TAR, where CDK9 modifies RNA polymerase II for the efficient copying of the viral genome.
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PMID:The ability of positive transcription elongation factor B to transactivate human immunodeficiency virus transcription depends on a functional kinase domain, cyclin T1, and Tat. 969 9


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