The cell cycle progression is governed by a family of kinases (cdk: cyclin dependent kinases) whose activities are regulated by binding to regulatory subunits called cyclins. During the cell cycle and activate form specific pairs of cdk and cyclins. The pair CDK1 with cyclins A and B governs the transition G 2 / M. During the cell cycle cdk levels remain relatively constant and the cyclins fluctuate, thus activating specific cdk. (more...)