Fig. 1

Overview of the regulation of the cell cycle. The cell cycle is depicted as a circle where each black arrow represents one phase of the cell cycle. Cells enter the cell cycle into the G1 phase, which is followed by the S phase, G2 phase and then mitosis (M). The cell cycle is regulated by CDKs (purple), their regulatory subunit cyclins (pink), CDK inhibitors such as p21 (light blue), and other regulatory kinases, such as the checkpoint kinases 1 and 2 (Chk1 and Chk2; yellow). The orange lines at the end of G1, G2 and during mitosis indicate cell cycle checkpoints where the cell is monitored for defects during replication and can respond by the p53 (green) pathway or the ATM/R (red) pathway, among others. Yellow circles with “M” indicate proteins known to be methylated on arginine residues and the dark blue circles with “P” indicate phosphorylation of pRB