X-ray sensitive mutants of Chinese hamster ovary cell line: radio-sensitivity of DNA synthesis.

6 mutants of the CHO cell line hypersensitive to ionizing radiation have been previously described (Jeggo et al., 1982; Jeggo and Kemp, 1983). In this report, the degree of radiosensitivity of DNA synthesis in these mutant strains has been investigated. 5 of the 6 mutant strains showed a greater degree of inhibition of DNA synthesis following gamma-irradiation compared to the wild-type strains, one mutant showed a similar response to the parent strain. An analysis of the size of the DNA made after irradiation in mutant and wild-type strains indicated that initiation events were more inhibited than chain elongations. This enhanced radiosensitivity is in contrast to results observed using ataxia telangiectasia fibroblasts, in which DNA synthesis is radioresistant in comparison to normal skin fibroblasts. These results are interpreted on the basis of sensitivity resulting from a defect in DNA repair in these mutant strains.