X-ray response of Chinese hamster ovary cells during the latter part of G2.

The ability of Chinese hamster ovary (CHO) cells to repair x-radiation damage during the transit from the late G2 to early M cell cycle stages was investigated by conventional dose-fractionation techniques. Despite their relatively high radiation sensitivity, CHO cells positioned in late G2 exhibit increased survival when a given dose of ionizing radiation is administered as two fractions (separated by 40-50 min) instead of as a single fraction. This increased survival apparently represents repair since neither cell cycle progression nor changes in the number of "effective targets" can account for the observed dose-sparing effect.