Specificity of Cdk activation in vivo by the two Caks Mcs6 and Csk1 in fission yeast

• Published in: The EMBO journal Vol. 20; no. 1-2; pp. 82 - 90
• Main Authors: Hermand, Damien, Westerling, Thomas, Pihlak, Arno, Thuret, Jean-Yves, Vallenius, Tea, Tiainen, Marianne, Vandenhaute, Jean, Cottarel, Guillaume, Mann, Carl, Mäkelä, Tomi P.
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 15.01.2001; Blackwell Publishing Ltd; Oxford University Press
• Subjects: Cak1; Cdk-activating kinases; Cloning, Molecular; Csk1; Csk1 protein; Cyclin-Dependent Kinases - metabolism; Enzyme Activation; Genetic Complementation Test; Glutathione Transferase - genetics; Humans; Mcs6; Mcs6 protein; Metazoa; Open Reading Frames; Phenotype; Phosphorylation; Protein Kinases - genetics; Protein Kinases - metabolism; Protein-Serine-Threonine Kinases - genetics; Protein-Serine-Threonine Kinases - metabolism; Recombinant Fusion Proteins - metabolism; Saccharomyces cerevisiae; Schizosaccharomyces - enzymology; Schizosaccharomyces - genetics; Schizosaccharomyces - growth & development; Schizosaccharomyces pombe; Schizosaccharomyces pombe Proteins; Substrate Specificity; Yeasts
• ISSN: 0261-4189; 1460-2075; 1460-2075
• DOI: 10.1093/emboj/20.1.82

Activating phosphorylation of cyclin‐dependent kinases (Cdks) is mediated by at least two structurally distinct types of Cdk‐activating kinases (Caks): the trimeric Cdk7–cyclin H–Mat1 complex in metazoans and the single‐subunit Cak1 in budding yeast. Fission yeast has both Cak types: Mcs6 is a Cdk7 ortholog and Csk1 a single‐subunit kinase. Both phosphorylate Cdks in vitro and rescue a thermosensitive budding yeast CAK1 strain. However, this apparent redundancy is not observed in fission yeast in vivo. We have identified mutants that exhibit phenotypes attributable to defects in either Mcs6‐activating phosphorylation or in Cdc2‐activating phosphorylation. Mcs6, human Cdk7 and budding yeast Cak1 were all active as Caks for Cdc2 when expressed in fission yeast. Although Csk1 could activate Mcs6, it was unable to activate Cdc2. Biochemical experiments supported these genetic results: budding yeast Cak1 could bind and phosphorylate Cdc2 from fission yeast lysates, whereas fission yeast Csk1 could not. These results indicate that Mcs6 is the direct activator of Cdc2, and Csk1 only activates Mcs6. This demonstrates in vivo specificity in Cdk activation by Caks.