X-ray and UV mutagenesis in two L5178Y cell strains differing in tumorigenicity, radiosensitivity, and DNA repair

L5178Y-R (LY-R) and L5178Y-S (LY-S) cells are inversely cross sensitive to X-rays and UV (254 nm) radiation (Dox = 0.94 and 0.69 Gy, Dqx = 0.32 and 0.010 Gy; Douv = 0.07 and 5.5 J m-2, Dquv = 3.8 and 1.6 J m-2, for LY-R and LY-S cells, respectively). Mutagenicity of the two cell strains at the hypoxanthine-guanine phosphoribosyl transferase (HGPRT) locus was examined using 6-thioguanine resistance as a marker. LY-S cells showed remarkably low mutability; the spontaneous mutation frequency of LY-S cells was at least two orders of magnitude lower than that for LY-R cells (less than or equal to 0.005 vs. approximately 2.5 mutants per 10(5) survivors). The induced mutation rates for X-rays were 0.95 +/- 0.14 and 0.35 +/- 0.09 mutants per Gy per 10(5) survivors, and for UV radiation, 21.5 +/- 8.2 and 0.04 +/- 0.02 mutants per J m-2 per 10(5) survivors, for LY-R and LY-S cells, respectively. The results suggest that LY-S cells are efficient in the repair of UV-induced damage but not of lesions produced by ionizing radiation. The reverse appears to be true for LY-R cells. In addition, the low mutability of LY-S cells suggests that the processing of pre-mutational lesions may lead to lethality in this strain.