FIGURE 2.

KSR1 is required for cell cycle re-entry following MMC treatment. A, diagram representing cell cycle arrest and the CBPI assay. The cells that complete mitosis and undergo cell cycle arrest at cytokinesis because of cytochalasin B treatment are binucleated. The cells that have undergone arrest earlier in the cell cycle and have not yet completed mitosis are mononucleated. KSR1^–/–, KSR1^+/+, or KSR1^–/– MEFs expressing ectopic KSR1 were treated with DNA-damaging agents (light gray bars) or left untreated (dark gray bars). The cells were treated with 0.5 μg/ml MMC for 2 h (B), 5 J/m² UV radiation (C), or 8 Gy IR (D). Following treatment, the cells were incubated with cytochalasin B for the indicated times and analyzed by CBPI assay. The percentage of binucleated cells is indicated. The values are the averages ± standard deviations of at least three independent experiments.