Rapid Degradation of the G1 Cyclin Cln2 Induced by CDK-Dependent Phosphorylation

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Science  15 Mar 1996:
Vol. 271, Issue 5255, pp. 1597-1601
DOI: 10.1126/science.271.5255.1597


Cyclins regulate the major cell cycle transitions in eukaryotes through association with cyclin-dependent protein kinases (CDKs). In yeast, G1 cyclins are essential, rate-limiting activators of cell cycle initiation. G1-specific accumulation of one G1 cyclin, Cln2, results from periodic gene expression coupled with rapid protein turnover. Site-directed mutagenesis of CLN2 revealed that its phosphorylation provides a signal that promotes rapid degradation. Cln2 phosphorylation is dependent on the Cdc28 protein kinase, the CDK that it activates. These findings suggest that Cln2 is rendered self-limiting by virtue of its ability to activate its cognate CDK subunit.