The CDK activity of the Cyclin A:Cdk2 complex is inhibited by phosphorylation at Tyr-15 by the WEE1 kinase (Gu et al. 1992, Wu et al. 2001). WEE1-mediated phosphorylation of cyclin A-bound CDK2 is positively regulated by CABLES1 (Wu et al. 2001).