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

The protein kinase p34(cdc2) plays a central role in controlling the G 2 to mitosis transition in all eukaryotic cells. It is regulated by pr otein-protein association and by multiple phosphorylations; one of the se phosphorylations is absolutely required for activity. Until recentl y, the molecular identity of the protein kinase that phosphorylates th is site was unknown. The subunits of this enzyme have been identified recently as p40(MO15), the catalytic subunit, and cyclin H, a regulato ry subunit. Similarities between this kinase and the p34(cdc2) family of protein kinases suggest how p40(MO15) itself may be regulated.