Abstract
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.
Publication types
-
Research Support, Non-U.S. Gov't
MeSH terms
-
Anaphase-Promoting Complex-Cyclosome
-
CDC28 Protein Kinase, S cerevisiae / antagonists & inhibitors
-
CDC28 Protein Kinase, S cerevisiae / physiology*
-
Cell Cycle*
-
Cyclin B*
-
Cyclin-Dependent Kinase Inhibitor Proteins
-
Cyclins / physiology*
-
Fungal Proteins / physiology*
-
Ligases / physiology
-
Saccharomyces cerevisiae / cytology*
-
Saccharomyces cerevisiae Proteins*
-
Ubiquitin-Conjugating Enzymes
-
Ubiquitin-Protein Ligase Complexes*
-
Ubiquitin-Protein Ligases
Substances
-
CLB5 protein, S cerevisiae
-
Cyclin B
-
Cyclin-Dependent Kinase Inhibitor Proteins
-
Cyclins
-
Fungal Proteins
-
SIC1 protein, S cerevisiae
-
Saccharomyces cerevisiae Proteins
-
CDC34 protein, S cerevisiae
-
Ubiquitin-Conjugating Enzymes
-
Ubiquitin-Protein Ligase Complexes
-
Anaphase-Promoting Complex-Cyclosome
-
Ubiquitin-Protein Ligases
-
CDC28 Protein Kinase, S cerevisiae
-
Ligases