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

Tat stimulation of human immunodeficiency virus type 1 (HIV-1) transcription requires Tat-dependent recruitment of human positive transcription elongation factor b (P-TEFb) to the HIV-1 promoter and the formation on the trans-acting response element (TAR) RNA of a P-TEFb-Tat-TAR ternary complex. We show here that the P-TEFb heterodimer of Cdk9-cyclin T1 is intrinsically incapable of forming a stable complex with Tat and TAR due to two built-in autoinhibitory mechanisms in P-TEFb. Both mechanisms exert little effect on the P-TEFb-Tat interaction but prevent the P-TEFb-Tat complex from binding to TAR RNA. The first autoinhibition arises from the unphosphorylated state of Cdk9, which establishes a P-TEFb conformation unfavorable for TAR recognition. Autophosphorylation of Cdk9 overcomes this inhibition by inducing conformational changes in P-TEFb, thereby exposing a region in cyclin T1 for possible TAR binding. An intramolecular interaction between the N- and C-terminal regions of cyclin T1 sterically blocks the P-TEFb-TAR interaction and constitutes the second autoinhibitory mechanism. This inhibition is relieved by the binding of the C-terminal region of cyclin T1 to the transcription elongation factor Tat-SF1 and perhaps other cellular factors. Upon release from the intramolecular interaction, the C-terminal region also interacts with RNA polymerase II and is required for HIV-1 transcription, suggesting its role in bridging the P-TEFb-Tat-TAR complex and the basal elongation apparatus. These data reveal novel control mechanisms for the assembly of a multicomponent transcription elongation complex at the HIV-1 promoter.
Mol Cell Biol 2000 Aug
PMID:Relief of two built-In autoinhibitory mechanisms in P-TEFb is required for assembly of a multicomponent transcription elongation complex at the human immunodeficiency virus type 1 promoter. 1091 73

Human immunodeficiency virus type 1 (HIV-1) Tat interacts with cyclin T1 (CycT1), a regulatory partner of CDK9 in the positive transcription elongation factor (P-TEFb) complex, and binds cooperatively with CycT1 to TAR RNA to recruit P-TEFb and promote transcription elongation. We show here that Tat also stimulates phosphorylation of affinity-purified core RNA polymerase II and glutathione S-transferase-C-terminal-domain substrates by CycT1-CDK9, but not CycH-CDK7, in vitro. Interestingly, incubation of recombinant Tat-P-TEFb complexes with ATP enhanced binding to TAR RNA dramatically, and the C-terminal half of CycT1 masked binding of Tat to TAR RNA in the absence of ATP. ATP incubation lead to autophosphorylation of CDK9 at multiple C-terminal Ser and Thr residues, and full-length CycT1 (amino acids 728) [CycT1(1-728)], but not truncated CycT1(1-303), was also phosphorylated by CDK9. P-TEFb complexes containing a catalytically inactive CDK9 mutant (D167N) bound TAR RNA weakly and independently of ATP, as did a C-terminal truncated CDK9 mutant that was catalytically active but unable to undergo autophosphorylation. Analysis of different Tat proteins revealed that the 101-amino-acid SF2 HIV-1 Tat was unable to bind TAR with CycT1(1-303) in the absence of phosphorylated CDK9, whereas unphosphorylated CDK9 strongly blocked binding of HIV-2 Tat to TAR RNA in a manner that was reversed upon autophosphorylation. Replacement of CDK9 phosphorylation sites with negatively charged residues restored binding of CycT1(1-303)-D167N-Tat, and rendered D167N a more potent inhibitor of transcription in vitro. Taken together, these results demonstrate that CDK9 phosphorylation is required for high-affinity binding of Tat-P-TEFb to TAR RNA and that the state of P-TEFb phosphorylation may regulate Tat transactivation in vivo.
Mol Cell Biol 2000 Sep
PMID:CDK9 autophosphorylation regulates high-affinity binding of the human immunodeficiency virus type 1 tat-P-TEFb complex to TAR RNA. 1095 91

Elongin is a transcription elongation factor that stimulates the rate of elongation by suppressing transient pausing by RNA polymerase II at many sites along the DNA. It is heterotrimeric in mammals, consisting of elongins A, B and C subunits, and bears overall similarity to a class of E3 ubiquitin ligases known as SCF (Skp1-Cdc53 (cullin)-F-box) complexes. A subcomplex of elongins B and C is a target for negative regulation by the von Hippel-Lindau (VHL) tumor-suppressor protein. Elongin C from Saccharomyces cerevisiae, Elc1, exhibits high sequence similarity to mammalian elongin C. Using NMR spectroscopy we have determined the three-dimensional structure of Elc1 in complex with a human VHL peptide, VHL(157-171), representing the major Elc1 binding site. The bound VHL peptide is entirely helical. Elc1 utilizes two C-terminal helices and an intervening loop to form a binding groove that fits VHL(157-171). Chemical shift perturbation and dynamics analyses reveal that a global conformational change accompanies Elc1/VHL(157-171) complex formation. Moreover, the disappearance of conformational exchange phenomena on the microsecond to millisecond time scale within Elc1 upon VHL peptide binding suggests a role for slow internal motions in ligand recognition.
J Mol Biol 2001 Sep 07
PMID:Solution structure and dynamics of yeast elongin C in complex with a von Hippel-Lindau peptide. 1154 95

To stimulate transcriptional elongation of HIV-1 genes, the transactivator Tat recruits the positive transcription elongation factor b (P-TEFb) to the initiating RNA polymerase II (RNAPII). We found that the activation of transcription by RelA also depends on P-TEFb. Similar to Tat, RelA activated transcription when tethered to RNA. Moreover, TNF-alpha triggered the recruitment of P-TEFb to the NF-kappaB-regulated IL-8 gene. While the formation of the transcription preinitiation complex (PIC) remained unaffected, DRB, an inhibitor of P-TEFb, prevented RNAPII from elongating on the IL-8 gene. Remarkably, DRB inhibition sensitized cells to TNF-alpha-induced apoptosis. Thus, NF-kappaB requires P-TEFb to stimulate the elongation of transcription and P-TEFb plays an unexpected role in regulating apoptosis.
Mol Cell 2001 Aug
PMID:NF-kappaB binds P-TEFb to stimulate transcriptional elongation by RNA polymerase II. 1154 35

Transcriptional elongation by RNA polymerase II (RNAPII) is regulated by the positive transcription elongation factor b (P-TEFb). P-TEFb is composed of Cdk9 and C-type cyclin T1 (CycT1), CycT2a, CycT2b, or CycK. The role of the C-terminal region of CycT1 and CycT2 remains unknown. In this report, we demonstrate that these sequences are essential for the activation of transcription by P-TEFb via DNA, i.e., when CycT1 is tethered upstream or downstream of promoters and coding sequences. A histidine-rich stretch, which is conserved between CycT1 and CycT2 in this region, bound the C-terminal domain of RNAPII. This binding was required for the subsequent expression of full-length transcripts from target genes. Thus, P-TEFb could mediate effects of enhancers on the elongation of transcription.
Mol Cell Biol 2002 Jan
PMID:Interaction between P-TEFb and the C-terminal domain of RNA polymerase II activates transcriptional elongation from sites upstream or downstream of target genes. 1173 44

The human immunodeficiency virus type 1 (HIV-1) Tat protein activates transcription elongation by stimulating the Tat-activated kinase (TAK/p-TEFb), a protein kinase composed of CDK9 and its cyclin partner, cyclin T1. CDK9 is able to hyperphosphorylate the carboxyl-terminal domain (CTD) of the large subunit of RNA polymerase during elongation. In addition to TAK, the transcription elongation factor Spt5 is required for the efficient activation of transcriptional elongation by Tat. To study the role of Spt5 in HIV transcription in more detail, we have developed a three-stage Tat-dependent transcription assay that permits the isolation of active preinitiation complexes, early-stage elongation complexes, and Tat-activated elongation complexes. Spt5 is recruited in the transcription complex shortly after initiation. After recruitment of Tat during elongation through the transactivation response element RNA, CDK9 is activated and induces hyperphosphorylation of Spt5 in parallel to the hyperphosphorylation of the CTD of RNA polymerase II. However, immunodepletion experiments demonstrate that Spt5 is not required for Tat-dependent activation of the kinase. Chase experiments using the Spt5-depleted extracts demonstrate that Spt5 is not required for early elongation. However, Spt5 plays an important role in late elongation by preventing the premature dissociation of RNA from the transcription complex at terminator sequences and reducing the amount of polymerase pausing at arrest sites, including bent DNA sequences. This novel biochemical function of Spt5 is analogous to the function of NusG, an elongation factor found in Escherichia coli that enhances RNA polymerase stability on templates and shows sequence similarity to Spt5.
Mol Cell Biol 2002 Feb
PMID:Spt5 cooperates with human immunodeficiency virus type 1 Tat by preventing premature RNA release at terminator sequences. 1180

Characterization of nine transposon-induced mutants of Rhizobium tropici with decreased salt tolerance (DST) allowed the identification of eight gene loci required for adaptation to high external NaCl. Most of the genes also were involved in adaptation to hyperosmotic media and were required to overcome the toxicity of LiCl. According to their possible functions, genes identified could be classified into three groups. The first group included two genes involved in regulation of gene expression, such as ntrY, the sensor element of the bacterial ntrY/ntrX two-component regulatory system involved in regulation of nitrogen metabolism, and greA, which encodes a transcription elongation factor. The second group included genes related to synthesis, assembly, or maturation of proteins, such as alaS coding for alanine-tRNA synthetase, dnaJ, which encodes a molecular chaperone, and a nifS homolog probably encoding a cysteine desulfurase involved in the maturation of Fe-S proteins. Genes related with cellular build-up and maintenance were in the third group, such as a noeJ-homolog, encoding a mannose-1-phosphate guanylyltransferase likely involved in lipopolysaccharide biosynthesis, and kup, specifying an inner-membrane protein involved in potassium uptake. Another gene was identified that had no homology to known genes but that could be conserved in other rhizobia. When inoculated on Phaseolus vulgaris growing under nonsaline conditions, all DST mutants displayed severe symbiotic defects: ntrY and noeJ mutants were impaired in nodulation, and the remaining mutants formed symbiosis with very reduced nitrogenase activity. The results suggest that bacterial ability to adapt to hyperosmotic and salt stress is important for the bacteroid nitrogen-fixing function inside the legume nodule and provide genetic evidence supporting the suggestion that rhizobia face severe environmental changes after their release into plant cells.
Mol Plant Microbe Interact 2002 Mar
PMID:Rhizobium tropici genes involved in free-living salt tolerance are required for the establishment of efficient nitrogen-fixing symbiosis with Phaseolus vulgaris. 1195 25

The FF domain is a 60 amino acid residue phosphopeptide-binding module found in a variety of eukaryotic proteins including the transcription elongation factor CA150, the splicing factor Prp40 and p190RHOGAP. We have determined the structure of an FF domain from HYPA/FBP11. The domain is composed of three alpha helices arranged in an orthogonal bundle with a 3(10) helix in the loop between the second and third alpha helices. The structure differs from those of other phosphopeptide-binding domains and represents a novel phosphopeptide-binding fold.
J Mol Biol 2002 Oct 25
PMID:The structure of an FF domain from human HYPA/FBP11. 1238 Dec 97

Cyclin T1, together with the kinase CDK9, is a component of the transcription elongation factor P-TEFb which binds the human immunodeficiency virus type 1 (HIV-1) transactivator Tat. P-TEFb facilitates transcription by phosphorylating the carboxy-terminal domain (CTD) of RNA polymerase II. Cyclin T1 is an exceptionally large cyclin and is therefore a candidate for interactions with regulatory proteins. We identified granulin as a cyclin T1-interacting protein that represses expression from the HIV-1 promoter in transfected cells. The granulins, mitogenic growth factors containing repeats of a cysteine-rich motif, were reported previously to interact with Tat. We show that granulin formed stable complexes in vivo and in vitro with cyclin T1 and Tat. Granulin bound to the histidine-rich domain of cyclin T1, which was recently found to bind to the CTD, but not to cyclin T2. Binding of granulin to P-TEFb inhibited the phosphorylation of a CTD peptide. Granulin expression inhibited Tat transactivation, and tethering experiments showed that this effect was due, at least in part, to a direct action on cyclin T1 in the absence of Tat. In addition, granulin was a substrate for CDK9 but not for the other transcription-related kinases CDK7 and CDK8. Thus, granulin is a cellular protein that interacts with cyclin T1 to inhibit transcription.
Mol Cell Biol 2003 Mar
PMID:The growth factor granulin interacts with cyclin T1 and modulates P-TEFb-dependent transcription. 1258 88

The multisubunit transcription elongation factor NELF (for negative elongation factor) acts together with DRB (5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole) sensitivity-inducing factor (DSIF)/human Spt4-Spt5 to cause transcriptional pausing of RNA polymerase II (RNAPII). NELF activity is associated with five polypeptides, A to E. NELF-A has sequence similarity to hepatitis delta antigen (HDAg), the viral protein that binds to and activates RNAPII, whereas NELF-E is an RNA-binding protein whose RNA-binding activity is critical for NELF function. To understand the interactions of DSIF, NELF, and RNAPII at a molecular level, we identified the B, C, and D proteins of human NELF. NELF-B is identical to COBRA1, recently reported to associate with the product of breast cancer susceptibility gene BRCA1. NELF-C and NELF-D are highly related or identical to the protein called TH1, of unknown function. NELF-B and NELF-C or NELF-D are integral subunits that bring NELF-A and NELF-E together, and coexpression of these four proteins in insect cells resulted in the reconstitution of functionally active NELF. Detailed analyses using mutated recombinant complexes indicated that the small region of NELF-A with similarity to HDAg is critical for RNAPII binding and for transcriptional pausing. This study defines several important protein-protein interactions and opens the way for understanding the mechanism of DSIF- and NELF-induced transcriptional pausing.
Mol Cell Biol 2003 Mar
PMID:Human transcription elongation factor NELF: identification of novel subunits and reconstitution of the functionally active complex. 1261 62


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