title: X-ray sensitive mutants of Chinese hamster ovary cells defective in double-strand break rejoining.
abstract: Six CHO mutants have previously been described as being sensitive to ionizing radiation and bleomycin treatment, with little or no cross sensitivity to UV-radiation (Jeggo and Kemp, 1983). Their ability to rejoin single- and double-strand breaks has been examined here. Using two techniques, gradient sedimentation and alkaline elution, no difference could be observed between wild-type and mutant strains in the initial number of single-strand breaks induced, the rate of rejoining, or the final level of single-strand breaks rejoined. Thus, a major inability to rejoin single-strand breaks is not the basis for sensitivity in these mutants. In contrast, all 6 mutants showed a decreased ability to rejoin the double-strand breaks induced by gamma-irradiation as measured by neutral elution. Rejoining of half of the breaks occurred in 37 min in wild-type cells and reached a maximum level of 72% after 2 h. All the mutants showed a decreased rate of rejoining, and the final level was 17% of that observed in the wild-type in the most defective mutant, and ranged from 35 to 69% in the other 5 mutants. These are the first mammalian cell mutants to be described with a defect in double-strand break rejoining.
mesh_terms: D000818:Animals; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D004260:DNA Repair / Q000528:radiation effects*; D004277:DNA, Single-Stranded / Q000528:radiation effects*; D005260:Female; D007700:Kinetics; D009154:Mutation; D010053:Ovary; D014466:Ultraviolet Rays; D014965:X-Rays
chemical_list: D004277:DNA, Single-Stranded