Cell cycle control and initiation of DNA replication in Saccharomyces cerevisiae

The cell cycle of budding yeast is controlled by a single cyclin-dependent protein kinase (Cdc28/Cdk1) which successively associates with the stage-specific activators Cln1-3 (G1 phase), Clb5,6 (S phase), Clb3,4 (S/G2 phase) and Clb1,2 (mitosis), The temporal pattern of these Cdk1/cyclin activities imposes a strict order of DNA replication events during the cycle: formation of a pre-replication complex at late M phase, initiation of replication at the G1/s transition, support of replication during S phase, and the prevention of re-replication at G2. A key component involved in S phase initiation is the Cdc6 protein, a transiently expressed DNA-independent ATP/GTPase interacting at late mitosis with an origin-recognizing complex.