Correlation of Survival with the Restoration of DNA Structure in X-Irradiated L5178Y S/S Cells

After exponentially growing populations of the radiosensitive S/S variant of the L5178Y murine leukemic lymphoblast were exposed to low doses of X rays (≤100 rad), the majority of the radiation-induced strand breaks in the DNA appeared to be rejoined within 5-10 hr. Subsequently, the DNA resolved slowly into a component that finally degraded into small pieces and a component that regained the size of the DNA in unirradiated cells long after irradiation (days). The fraction of the latter component correlated directly with the fraction of surviving cells. A similar correlation was found when semisynchronous populations of the S/S variant were X-irradiated (≤200 rad) during the radioresistant phase of the cell cycle.