Figure 1.

Mouse ES cells carrying either one or two disrupted Msh2 genes appear tolerant to lethal effects of low-level radiation exposure. Displayed are clonogenic survival curves obtained from analysis of wt mouse ES cells (Msh2^+/+) and ES cells carrying disrupted Msh2 genes (Msh2^+/− and Msh2^−/−) after (A) prolonged (24, 48, and 72 h) exposure to low-level ionizing radiation (0.004 Gy/min) or after (B) treatment with acute dose ionizing radiation (1.0 Gy/min). Each symbol represents the mean of multiple, triplicate experiments; the SEM is shown by using error bars. In some cases, the error bars are smaller than the symbol.