The expression of these cyclins in temporally distinct waves is, in part, responsible for the orderly progression of events in the cell cycle. The 2 major classes of cyclins, G 1 and B type, can be divided into subclasses on the basis of both primary sequence and pattern of expression. Each class appears to be optimally suited for a specific function in cell cycle. This specificity is due, in part, to the pattern of accumulation of the cyclins. We focus on regulation of initiation of the cell cycle during G 1 phase in the budding yeast Saccharomyces cerevisiae .
Initiation involves a complex choreography of events driven by the sequential activation of CDKs.
Efforts are under way to elucidate the mechanism of activation of G 1 -specific transcription. Accumulation of the proteins Cln1 and Cln2 drives early events in the development of the presumptive daughter cell. These key proteins include the G 1 cyclins themselves and Sic1, a specific inhibitor of CDK activity associated with B-type cyclins. Grr1 mediates the specific interaction of SCF with phosphorylated Cln2. We are analyzing Grr1 and Cln2 to understand the basis for that recognition.