title: A feed forward circuit comprising Spt6, Ctk1 and PAF regulates Pol II CTD phosphorylation and transcription elongation.
abstract: The C-terminal domain (CTD) of RNA polymerase II is sequentially modified for recruitment of numerous accessory factors during transcription. One such factor is Spt6, which couples transcription elongation with histone chaperone activity and the regulation of H3 lysine 36 methylation. Here, we show that CTD association of Spt6 is required for Ser2 CTD phosphorylation and for the protein stability of Ctk1 (the major Ser2 CTD kinase). We also find that Spt6 associates with Ctk1, and, unexpectedly, Ctk1 and Ser2 CTD phosphorylation are required for the stability of Spt6-thus revealing a Spt6-Ctk1 feed-forward loop that robustly maintains Ser2 phosphorylation during transcription. In addition, we find that the BUR kinase and the polymerase associated factor transcription complex function upstream of the Spt6-Ctk1 loop, most likely by recruiting Spt6 to the CTD at the onset of transcription. Consistent with requirement of Spt6 in histone gene expression and nucleosome deposition, mutation or deletion of members of the Spt6-Ctk1 loop leads to global loss of histone H3 and sensitivity to hydroxyurea. In sum, these results elucidate a new control mechanism for the regulation of RNAPII CTD phosphorylation during transcription elongation that is likely to be highly conserved.
authors.affiliation: Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA and Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
authors.forename: Raghuvar
authors.initials: R
authors.lastname: Dronamraju
authors.forename: Brian D
authors.initials: BD
authors.lastname: Strahl
mesh_terms: D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D016213:Cyclins / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D056488:Histone Chaperones; D009687:Nuclear Proteins / Q000378:metabolism*; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D055550:Protein Stability; D017434:Protein Structure, Tertiary; D012319:RNA Polymerase II / Q000737:chemistry / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D061805:Transcription Elongation, Genetic; D035602:Transcriptional Elongation Factors / Q000378:metabolism*
chemical_list: C414164:Bur2 protein, S cerevisiae; C118305:CTDK-I protein complex, S cerevisiae; D016213:Cyclins; D056488:Histone Chaperones; D009687:Nuclear Proteins; C065456:SPT6 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D035602:Transcriptional Elongation Factors; D011494:Protein Kinases; D018844:Cyclin-Dependent Kinases; C414163:SGV1 protein, S cerevisiae; D012319:RNA Polymerase II