The Cak1p protein kinase is required at G1/S and G2/M in the budding yeast cell cycle.
The CAK1 gene encodes the major CDK-activating kinase (CAK) in budding yeast and is required for activation of Cdc28p for cell cycle progression from G2 to M phase. Here we describe the isolation of a mutant allele of CAK1 in a synthetic lethal screen with the Sit4 protein phosphatase. Analysis of several different cak1 mutants shows that although the G2 to M transition appears most sensitive to loss of Cak1p function, Cak1p is also required for activation of Cdc28p for progression from G1 into S phase. Further characterization of these mutants suggests that, unlike the CAK identified from higher eukaryotes, Cak1p of budding yeast may not play a role in general transcription. Finally, although Cak1 protein levels and in vitro protein kinase activity do not fluctuate during the cell cycle, at least a fraction of Cak1p associates with higher molecular weight proteins, which may be important for its in vivo function.
Sutton
A
A
Department of Biochemistry and Cell Biology, State University of New York, Stony Brook 11794, USA. sutton@mcbsgi.bio.sunysb.edu
Freiman
R
R
D017489:CDC28 Protein Kinase, S cerevisiae / Q000235:genetics / Q000378:metabolism; D002453:Cell Cycle / Q000502:physiology*; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D016193:G1 Phase / Q000502:physiology; D016195:G2 Phase / Q000502:physiology; D005800:Genes, Fungal / Q000502:physiology; D005804:Genes, Lethal / Q000502:physiology; D009154:Mutation; D010749:Phosphoprotein Phosphatases / Q000502:physiology; D010766:Phosphorylation; D011233:Precipitin Tests; D054648:Protein Phosphatase 2; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D011506:Proteins / Q000378:metabolism; D012331:RNA, Fungal / Q000032:analysis; D012333:RNA, Messenger / Q000032:analysis; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D014158:Transcription, Genetic / Q000235:genetics; D000095043:Cyclin-Dependent Kinase-Activating Kinase
D011506:Proteins; D012331:RNA, Fungal; D012333:RNA, Messenger; D029701:Saccharomyces cerevisiae Proteins; D017346:Protein Serine-Threonine Kinases; D017489:CDC28 Protein Kinase, S cerevisiae; D018844:Cyclin-Dependent Kinases; C058605:PHO85 protein, S cerevisiae; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; C104343:SIT4 protein, S cerevisiae; D000095043:Cyclin-Dependent Kinase-Activating Kinase