Bur1 kinase is required for efficient transcription elongation by RNA polymerase II.
The Saccharomyces cerevisiae cyclin-dependent kinase (CDK) Bur1 (Sgv1) may be homologous to mammalian Cdk9, which functions in transcriptional elongation. Although Bur1 can phosphorylate the Rpb1 carboxy-terminal domain (CTD) kinase in vitro, it has no strong specificity within the consensus heptapeptide YSPTSPS for Ser2 or Ser5. BUR1 mutants are sensitive to the drugs 6-azauracil and mycophenolic acid and interact genetically with the elongation factors Ctk1 and Spt5. Chromatin immunoprecipitation experiments show that Bur1 and its cyclin partner Bur2 are recruited to transcription elongation complexes, cross-linking to actively transcribing genes. Interestingly, Bur1 shows reduced cross-linking to transcribed regions downstream of polyadenylation sites. In addition, bur1 mutant strains have a reduced cross-linking ratio of RNA polymerase II at the 3' end of genes relative to promoter regions. Phosphorylation of CTD serines 2 and 5 appears normal in mutant cells, suggesting that Bur1 is not a significant source of cotranscriptional Rpb1 phosphorylation. These results show that Bur1 functions in transcription elongation but may phosphorylate a substrate other than the CTD.
Keogh
Michael-Christopher
MC
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA.
Podolny
Vladimir
V
Buratowski
Stephen
S
D002843:Chromatin / Q000378:metabolism; D018844:Cyclin-Dependent Kinases / Q000235:genetics / Q000502:physiology*; D000939:Epitopes / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D005800:Genes, Fungal; D005982:Glutathione Transferase / Q000378:metabolism; D010641:Phenotype; D017354:Point Mutation; D011494:Protein Kinases / Q000032:analysis; D012319:RNA Polymerase II / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000502:physiology*; D013696:Temperature; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic
D002843:Chromatin; D000939:Epitopes; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D005982:Glutathione Transferase; D011494:Protein Kinases; C060137:carboxy-terminal domain kinase; D018844:Cyclin-Dependent Kinases; C414163:SGV1 protein, S cerevisiae; D012319:RNA Polymerase II