fig1

Figure 1. CDK-cyclin complexes and their function in cell cycle. Each CDK is shown in complex with its corresponding cyclin. For clarity, only few substrates are included. CDKs 1, 2, 4 and 6 are classical CDKs involved in the regulation of cell-cycle progression and transition from G1 to S phase. CDK1 in complex with cyclins A and B regulate G2/M transition and mitosis together with CDK11-CycL. CDK3 is involved in the control of the cell-cycle interphase. Activity of these CDK-cyclin complexes is regulated by other CDKs including CDK7 (in complex with its cyclin H and Mat1), CKIs (p15, p16, p18, p19, p27, p21 and p57) and regulatory elements such as the Rb. CDK7 functions in the regulation of several other CDKs via phosphorylation and is controlled by CDK8 in complex with its cyclin C. *Nonphosphorylated p27. Single letters stand for cyclins, for instance H is cyclin H. CKIs: cyclin-dependent kinase inhibitors; CDK: cyclin-dependent kinase; Rb: retinoblastoma protein; G1: growth phase; S: DNA synthesis; G2: second growth phase; M: mitosis; G0: resting phase; E2F: E2 transcription factor