The fission yeast S-phase cyclin Cig2 can drive mitosis.

Commitment to mitosis is regulated by cyclin-dependent kinase (CDK) activity. In the fission yeast Schizosaccharomyces pombe, the major B-type cyclin, Cdc13, is necessary and sufficient to drive mitotic entry. Furthermore, Cdc13 is also sufficient to drive S phase, demonstrating that a single cyclin can regulate alternating rounds of replication and mitosis, and providing the foundation of the quantitative model of CDK function.

Comparative functional genomics of the fission yeasts.

The fission yeast clade--comprising Schizosaccharomyces pombe, S. octosporus, S. cryophilus, and S.