The B-type cyclin kinase inhibitor p40SIC1 controls the G1 to S transition in S. cerevisiae

Etienne Schwob, Thomas Böhm, Michael D. Mendenhall, Kim Nasmyth

Research output: Contribution to journalArticlepeer-review

787 Scopus citations


When yeast cells reach a critical size, they initiate bud formation, spindle pole body duplication, and DNA replication almost simultaneously. All three events depend on activation of Cdc28 protein kinase by the G1 cyclins Cln1, -2, and -3. We show that DNA replication also requires activation of Cdc28 by B-type (Clb) cyclins. A sextuple clb1-6 mutant arrests as multibudded G1 cells that resemble cells lacking the Cdc34 ubiquitin-conjugating enzyme. cdc34 mutants cannot enter S phase because they fail to destroy p40SIC1, which is a potent inhibitor of Clb but not Cln forms of the Cdc28 kinase. In wild-type cells, p40SIC1 protein appears at the end of mitosis and disappears shortly before S phase. Proteolysis of a cyclin-specific inhibitor of Cdc28 is therefore an essential aspect of the G1 to S phase transition.

Original languageEnglish
Pages (from-to)233-244
Number of pages12
Issue number2
StatePublished - Oct 21 1994

Bibliographical note

Funding Information:
We would especially like to acknowledge the contributions made by Uttam Surana and Angelika Amon, who first noticed that Clb2 protein fails to activate Cdc26 in cdc34 mutants. We would also like to thank Christian Dahmann, whose data is presented in Figure 2A, and Angelika Amon for the data presented in Figure 48. We are grateful to Gotthold Schaffner, Robert Kurzbauer, Ivan Botto, Sissy Aigner for DNA sequencing and oligonucleotides synthesis, and Hannes Tkad-letz for photographs. We thank Christian Koch and Christian Dahmann for comments on the manuscript as well as Bruce Futcher, Kim Arndt, and Stefan Jentsch for plasmids, strains, and antibodies. T. B. was supported by the Jubileumsfondprojekt 4637 of the Austrian National Bank and by Fond zur Wissenshaftlichen Forderung grant PO9979/ MOB. M. D. M. acknowledges the American Cancer Society (grant CB-70B) for funding.

ASJC Scopus subject areas

  • General Biochemistry, Genetics and Molecular Biology


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