Fig. 2

Cyclin-dependent kinases (CDKs) cell cycle. CDKs and their cyclin partners form complexes, regulating the progression through the cell cycle (upper left panel). In early G1 phase (G1-pm), retinoblastoma protein (pRb) becomes phosphorylated by the complex, a pair of cyclin-D and CDK4/6 (upper right panel). In late G1 phase (G1-ps), pRb is hyper-phosphorylated by cyclin-E/CDK2 complex, undergoing a large conformational change. This conformational change fails to assemble with E2F, a transcription factor, which promotes to progress the G1/S transition. Cyclins bind with the dependent kinases and their concentration varies during the cell cycle (lower left panel). A crystal structure illustrates an example of cyclin/CDK complex (PDB: 2W99) (lower right panel). Apo-CDKs exhibit little kinase activity; CDKs become active kinases when interacting with the regulatory protein called a cyclin