A mouse-cell mutant sensitive to ionizing radiation is hypermutable by low doses of gamma-radiation

The mutant mouse lymphoma cell M10, which is sensitive to methyl methanesulfonate and ionizing radiation, was compared with the parental L5178Y cells for mutation induction after gamma-irradiation. The rate of induced mutations to 6-thioguanine resistance in L5178Y cells was 2-3 X 10(-7) per R, as determined after exposures ranging from 25 to 500 R. The induced mutation frequency per unit dose per locus in M10 cells was about 4 times higher than that in L5178Y cells at the lower doses of exposure (25-75 R), but it declined sharply at the higher doses of gamma-rays (100-150 R). The rate of induced mutation per unit cell killing in M10 cells was nearly the same as that in L5178Y cells when they were compared at the levels of lower cell killing.