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.

• PMID: 7954792
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Reference Type

Journal Article | Research Support, Non-U.S. Gov't

Authors

Schwob E, Böhm T, Mendenhall MD, Nasmyth K

Primary Lit For

CDC34 | CDC4 | CDC53 | CLB6 | CLB5 | SIC1 | SCF-Cdc4 ubiquitin ligase complex

Additional Lit For

CDC28 | CLB1 | CLB3 | CLN1 | CLB4 | SCF-Grr1 ubiquitin ligase complex | SCF-Mdm30 ubiquitin ligase complex | SCF-Ufo1 ubiquitin ligase complex | SCF-Das1 ubiquitin ligase complex | SCF-MET30 E3 ubiquitin ligase complex

Review For