title: Characterization of the Schizosaccharomyces pombe Cdk9/Pch1 protein kinase: Spt5 phosphorylation, autophosphorylation, and mutational analysis.
abstract: Schizosaccharomyces pombe Cdk9/Pch1 protein kinase is a functional ortholog of the essential Saccharomyces cerevisiae Bur1/Bur2 kinase and a putative ortholog of metazoan P-TEFb (Cdk9/cyclin T). SpCdk9/Pch1 phosphorylates of the carboxyl-terminal domain (CTD) of the S. pombe transcription elongation factor Spt5, which consists of 18 tandem repeats of a nonapeptide of consensus sequence 1TPAWNSGSK9. We document the divalent cation dependence and specificity of SpCdk9/Pch1, its NTP dependence and specificity, the dependence of Spt5-CTD phosphorylation on the number of tandem nonamer repeats, and the specificity for phosphorylation of the Spt5-CTD on threonine at position 1 within the nonamer element. SpCdk9/Pch1 also phosphorylates the CTD heptaptide repeat array of the largest subunit of S. pombe RNA polymerase II (consensus sequence YSPTSPS) and does so exclusively on serine. SpCdk9/Pch1 catalyzes autophosphorylation of the kinase and cyclin subunits of the kinase complex. The distribution of phosphorylation sites on SpCdk9 (86% Ser(P), 11% Thr(P), 3% Tyr(P)) is distinct from that on Pch1 (2% Ser(P), 98% Thr(P)). We conducted a structure-guided mutational analysis of SpCdk9, whereby a total of 29 new mutations of 12 conserved residues were tested for in vivo function by complementation of a yeast bur1Delta mutant. We identified many lethal and conditional mutations of side chains implicated in binding ATP and the divalent cation cofactor, phosphoacceptor substrate recognition, and T-loop dynamics. We surmise that the lethality of the of T212A mutation in the T-loop reflects an essential phosphorylation event, insofar as the conservative T212S change rescued wild-type growth; the phosphomimetic T212E change rescued growth at 30 degrees C; and the effects of mutating the T-loop threonine were phenocopied by mutations in the three conserved arginines predicted to chelate the phosphate on the T-loop threonine.
authors.affiliation: Molecular Biology Program, Sloan-Kettering Institute, New York, New York 10021, USA.
authors.forename: Yi
authors.initials: Y
authors.lastname: Pei
authors.forename: Stewart
authors.initials: S
authors.lastname: Shuman
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D001120:Arginine / Q000737:chemistry; D001665:Binding Sites; D002412:Cations; D002868:Chromosomal Proteins, Non-Histone; D042863:Cyclin-Dependent Kinase 9 / Q000737:chemistry* / Q000378:metabolism; D016213:Cyclins / Q000737:chemistry* / Q000378:metabolism; D004252:DNA Mutational Analysis; D004305:Dose-Response Relationship, Drug; D005982:Glutathione Transferase / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008957:Models, Genetic; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010455:Peptides / Q000737:chemistry; D010766:Phosphorylation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000378:metabolism; D012568:Schizosaccharomyces / Q000201:enzymology*; D029702:Schizosaccharomyces pombe Proteins; D017386:Sequence Homology, Amino Acid; D012694:Serine / Q000378:metabolism; D013997:Time Factors; D035602:Transcriptional Elongation Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D002412:Cations; D002868:Chromosomal Proteins, Non-Histone; D016213:Cyclins; C105853:Pch1 protein, S pombe; D010455:Peptides; D012333:RNA, Messenger; D029702:Schizosaccharomyces pombe Proteins; D035602:Transcriptional Elongation Factors; C069940:SPT5 transcriptional elongation factor; D012694:Serine; D000255:Adenosine Triphosphate; D001120:Arginine; D005982:Glutathione Transferase; D042863:Cyclin-Dependent Kinase 9