Isolation and partial characterization of mutagen-sensitive and DNA repair mutants of Chinese hamster fibroblasts.

Through a new approach, we have sought to isolate ultraviolet light (UV)-sensitive and DNA repair mutant Chinese hamster fibroblasts. The procedure consisted of 1) mutation induction by 5-bromodeoxyuridine (Brd U)-blacklight and UV treatments; 2) incorporation of 3H-thymidine in repair-proficient cells at high temperature (38.5 degrees C) following UV damage; 3) cold holding (4.0 degrees C) of these cells to induce tritium killing; and 4) recovery and testing of repair-deficient and UV-sensitive cells which have survived and formed colonies at low temperature (34.0 degrees C). In our initial attempt at this protocol, we isolated 72 surviving colonies from 2 x 10(7) cells plated for selection. Of the 72 colonies, 20 demonstrated potential interest and four were selected for extensive study. One, identified as UVs-7, is slightly more sensitive to UV, but not sensitive to X rays or N-acetoxy-2-acetylaminofluorene (NAc-AAF). The mutant exhibits a highly reduced level of unscheduled DNA synthesis (UDS), as compared to the parental line. Two additional lines, UVs-40 UVs-44, are sensitive to UV, X ray, N-methyl-N-nitro-N-nitrosoguanidine (MNNG), and NAc-AAF, but exhibit normal UDS. A fourth line, UVr-23, has enhanced UDS, is resistant to UV, but exhibits no difference in sensitivity to x ray or NAc-AAf. These mutants are all stable, and should be useful for the study of mammalians DNA repair processes and mechanisms of mutagenesis.