title: P-TEFb containing cyclin K and Cdk9 can activate transcription via RNA.
abstract: Different positive transcription elongation factor b (P-TEFb) complexes isolated from mammalian cells contain a common catalytic subunit (Cdk9) and the unique regulatory cyclins CycT1, CycT2a, CycT2b, or CycK. The role of CycK as a transcriptional cyclin was demonstrated in this study. First, CycK activated transcription when tethered heterologously to RNA, which required the kinase activity of Cdk9. Although this P-TEFb could phosphorylate the C-terminal domain (CTD) of RNA polymerase II (RNAPII) in vitro, in contrast to CycT1 and CycT2, CycK did not activate transcription when tethered to DNA. Interestingly, when the C termini of CycT1 and CycT2 or only the histidine-rich stretch from positions 481 to 551 in CycT1 were added to CycK, the extended chimeras activated transcription equivalently via DNA. Moreover, these transcriptional effects required the CTD of RNAPII in cells. Thus, CycK functions as P-TEFb only via RNA, which suggests the presence of cellular RNA-bound activators that require CycK for their transcriptional activity.
authors.affiliation: Department of Medicine, University of California at San Francisco, California 94143-0703, USA.
authors.forename: Xin
authors.initials: X
authors.lastname: Lin
authors.forename: Ran
authors.initials: R
authors.lastname: Taube
authors.forename: Koh
authors.initials: K
authors.lastname: Fujinaga
authors.forename: B Matija
authors.initials: BM
authors.lastname: Peterlin
mesh_terms: D001665:Binding Sites; D015153:Blotting, Western; D020134:Catalytic Domain; D002460:Cell Line; D042863:Cyclin-Dependent Kinase 9; D018844:Cyclin-Dependent Kinases / Q000737:chemistry / Q000378:metabolism*; D016213:Cyclins / Q000378:metabolism*; D006801:Humans; D008954:Models, Biological; D009154:Mutation; D010957:Plasmids / Q000378:metabolism; D042925:Positive Transcriptional Elongation Factor B; D011233:Precipitin Tests; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry* / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D012313:RNA / Q000378:metabolism*; D012319:RNA Polymerase II / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D013997:Time Factors; D014158:Transcription, Genetic
chemical_list: C113028:CCNK protein, human; D016213:Cyclins; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D012313:RNA; D042925:Positive Transcriptional Elongation Factor B; D017346:Protein Serine-Threonine Kinases; C467969:CDK9 protein, human; D042863:Cyclin-Dependent Kinase 9; D018844:Cyclin-Dependent Kinases; D012319:RNA Polymerase II