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  • The EMBO Journal (2001) 20, 82 - 90
  • doi:10.1093/emboj/20.1.82

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

Damien Hermand1,2,6, Thomas Westerling1,6, Arno Pihlak1,6, Jean-Yves Thuret3,6, Tea Vallenius1, Marianne Tiainen1, Jean Vandenhaute2, Guillaume Cottarel4, Carl Mann3 and Tomi P. Mäkelä1,5

  1. Haartman Institute & Biocentrum Helsinki, University of Helsinki, 00014 Helsinki, Finland
  2. Laboratoire de Génétique Moléculaire (GEMO), University of Namur (FUNDP), 61 Rue de Bruxelles, 5000 Namur, Belgium
  3. Service de Biochimie et Genetique Moléculaire, CEA/Saclay, F-91191 Gif-sur-Yvette Cedex, France
  4. Genome Therapeutics Corp., 100 Beaver Street, Waltham, MA 02154, USA
  5. HUCH Laboratory Diagnostics, 00029 HYKS, Finland
  6. D.Hermand & T.Westerling and A.Pihlak & J.-Y.Thuret, respectively, contributed equally to this work

Correspondence to:

Tomi P. Mäkelä, E-mail: tomi.makela@helsinki.fi

Received 2 November 2000; Accepted 20 November 2000; Revised 20 November 2000

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.

  • Keywords:

    • Cak1,
    • Cdk-activating kinases,
    • Csk1,
    • Mcs6