PHOSPHATE-REGULATED INACTIVATION OF THE KINASE PHO80-PHO85 BY THE CDKINHIBITOR PHO81

A complex consisting of the cyclin-dependent kinase (CDK) PHO85 and th e cyclin PHO80 phosphorylates and is thought to inactivate the transcr iption factor PHO4 when yeast cells are grown in medium containing hig h concentrations of phosphate. The CDK inhibitor PHO81 inhibits the ki nase activity of the PHO80-PHO85 complex when Saccharomyces cerevisiae cells are grown in medium depleted of phosphate. A region of PHO81 wi th similarity to the mammalian CDK inhibitor p16(INK4) is sufficient f or inhibition in vitro. These studies demonstrate that CDK inhibitors are used to regulate kinases involved in processes other than cell cyc le control and suggest that the ankyrin repeat motif may be commonly u sed for interaction with cyclin-CDK complexes.