Studies on three mutagen-sensitive mutants of mouse L5178Y cells. I. Characterization of the hybrids between L5178Y and mutagen-sensitive mutants.

Three mutagen-sensitive mutants, MS-1, M10 and Q31, have been isolated from mouse L5178Y cells. MS-1 cells are sensitive to methyl methanesulfonate (MMS), M10 cells are cross-sensitive to X-rays, MMS and 4-nitroquinoline 1-oxide (4NQO), and Q31 cells are cross-sensitive to UV and 4NQO. Lines resistant to 6-thioguanine (TGr) and 5-bromo-2'-deoxyuridine (BUr) were isolated from L5178Y and these three mutagen -sensitive mutants. All the TGr lines were sensitive to 5-bromo-2'-deoxyuridine and HAT medium and all the BUr lines were sensitive to 6-thioguanine and HAT medium. The hybrids homozygous for the mutagen-sensitive markers showed nearly the same sensitivity to UV, 4NQO, X-rays and MMS as their parental TGr and BUr lines. The hybrids constructed by fusing L5178Y BUr and TGr lines from each of MS-1, M10 and Q31 displayed the normal UV, X-ray and MMS resistancy of L5178Y cells. Thus the UV-, X-ray- and MMS-sensitive markers in MS-1, M10 and Q31 were recessive in somatic cell hybrids. The 4NQO-sensitive phenotype, however, behaved codominantly in somatic cell hybrids.