Fig. 2. Mitoses observed over the time course after irradiation in two p53 mutated cell lines. (A) After 10 Gy irradiation, cell samples were taken for 4 days and assessed by western blotting for the presence of p34^cdc2 and Tyr15-phosphorylated p34^cdc2. The delay in G2 for Namalwa and WI-L2-NS cells shown in Fig. 1 was associated with prominent Tyr15 phosphorylation of p34^cdc2 thus indicating a decrease in p34^cdc2 activity. The control level of p34^cdc2 activity was restored by day 3 (WI-L2-NS) or 4 (Namalwa) after irradiation. (B) The number of cells undergoing mitosis was assessed every day for 10 days by light microscopy, compared with untreated control cells and expressed as the mitotic index. These data show that adaptation of G2 arrest was followed by accumulation of WI-L2-NS (black diamonds) and Namalwa (open square) cells in mitosis. The drop in mitosis in the Namalwa cell line after 10 Gy, following the initial accumulation, is a result of mitotic failure. These data represent averages from three experiments and bars represent standard deviations.