Figure 5. Rad9^Ser272 is phosphorylated during normal cell cycle in an ATM dependent manner. (A) Cell cycle progression and Rad9^S272 phosphorylation after double thymidine block with (right) and without KU55933 treatment (10 µM) (left). (B) Rad9^Ser272 phosphorylation in sorted cells with (right) and without KU55933 (10 µM) treatment (left).