part of Phosphorylation in cytosol G2-M-phase transition Phosphorylation of Cdc2 by Cdk7 in cytosol IEV:0001133 IMR:0100597 IMR:0100603 Phosphorylation of Cdk1 by Cdk7 in cytosol UniProt:P50613, Stabilizes the cyclin H-CDK7 complex to form a functional CDK-activating kinase (CAK) enzymatic complex. CAK activates the cyclin-associated kinases CDC2/CDK1, CDK2, CDK4 and CDK6 by threonine phosphorylation. CAK complexed to the core-TFIIH basal transcription factor activates RNA polymerase II by serine phosphorylation of the repetitive carboxyl-terminus domain (CTD) of its large subunit (POLR2A), allowing its escape from the promoter and elongation of the transcripts. Involved in cell cycle control and in RNA transcription by RNA polymerase II. event