Figure 1).

Cell cycle steps (G0, G1, S and M) and their associated cyclin-dependent kinase (CDK)-cyclin complex holoenzyme and CDK inhibitors. There are two families of CDK inhibitors: inhibitors of CDL 4 (INK4) (p15, p16) and CDK interacting protein/inhibitory protein (Cip/Kip) (p21, p27)