THE FUNCTION(S) OF CAK, THE P34(CDC2)-ACTIVATING KINASE

The protein kinase p34(cdc2) plays a central role in controlling the G2 to mitosis transition in all eukaryotic cells. It is regulated by protein-protein association and by multiple phosphorylations; one of these phosphorylations is absolutely required for activity. Until recently, the molecular identity of the protein kinase that phosphorylates this site was unknown. The subunits of this enzyme have been identified recently as p40(MO15), the catalytic subunit, and cyclin H, a regulatory subunit. Similarities between this kinase and the p34(cdc2) family of protein kinases suggest how p40(MO15) itself may be regulated.