A Predictive Scale for Evaluating Cyclin-dependent Kinase Substrates. A Comparison of P34cdc2 and P33cdk2

Protein phosphorylation by members of the Cdk (cyclin-dependent kinase) family of protein kinases is necessary for progression through the cell cycle. However, the primary sequence determinants of Cdk substrate specificity have yet to be examined quantitatively. We have used a panel of glutathione S-transferase peptide fusions to investigate the fine-structure specificity of p33(cdk2) and p34(cdc2). Our data indicate that the generally held consensus sequences for p34(cdc2) represent a significant oversimplification of its true specificity and that this specificity is conserved between species. p33(cdk2) and p34(cdc2) have similar but distinct substrate specificities that are affected modestly by the associated cyclin subunit. We derive specific values of phosphorylation efficiencies by these enzymes that can be used to estimate the phosphorylation potential of proposed Cdk substrates.