Résumé
13-type cyclin destruction is necessary for exit from mitosis and the initiation of a new cell cycle. Through the isolation of mutants, we have identified three essential yeast genes,
CDC16, CDC23, and
CSE1, which are required for proteolysis of the B-type cyclin CLB2 but not of other unstable proteins.
cdc23-1 mutants are defective in both entering and exiting anaphase. Their failure to exit anaphase can be explained by defective cyclin proteolysis.
CDC23 is required at the metaphase/anaphase transition to separate sister chromatids, and we speculate that it might promote proteolysis of proteins that hold sister chromatids together. Proteolysis of CLB2 is initiated in early anaphase, but a fraction of CLB2 remains stable until anaphase is complete.