a, CDK2 activity traces of cells exposed to inhibitors of ATM (5 μM KU-60019), ATR (2 μM AZ-20), and DNA-PK (1 μM NU-7441) (marked in grey), starting 5 h after a control pulse or a 20-min NCS pulse (marked in purple). Cells undergoing mitosis within 1 h before drug treatment were selected for analysis. b, Averaged p21 intensity traces in response to a 20-min NCS pulse (200 ng ml−1) in MCF7 cells. Cells were selected for which NCS was applied during a 4-h time window after mitosis. Data are mean ± 95% confidence intervals (n = 79 cells).