DNA repair-deficient Chinese hamster ovary cells exhibiting differential sensitivity to gamma rays under aerobic and hypoxic conditions.

The survival of the wild-type parent and two mutant lines of Chinese hamster cells, known to be defective in DNA repair, has been determined as a function of exposure to gamma rays under aerobic and hypoxic conditions. When compared to the wild-type line, one of the mutants selected for sensitivity to ethyl methyl sulfonate (EMS), and known to be defective in the repair of DNA strand breaks, exhibits a markedly enhanced sensitivity to aerobic irradiation but a reduced enhancement to hypoxic irradiation and thus an enhanced oxygen enhancement ratio (OER). In contrast, the other line, known to be defective in the incision step of excision repair, exhibits the reverse pattern of sensitivity and hence a reduced OER. The results are compared to findings in bacterial mutants and cells obtained from ataxia telangiectasia (AT) patients and heterozygotes.