A Mutation (radA100) inEscherichia ColiThat Selectively Sensitizes Cells Grown in Rich Medium to X- or U.V.-radiation, or Methyl Methanesulphonate

Abstract

The radA100 mutant was isolated from Escherichia coli K-12 after mutagenesis with N-methyl-N''-nitrosoguanidine and selection from .gamma.-radiation sensitivity. The radA gene is located between the serB and deoC loci (at 99.6 min) on the E. coli K-12 linkage map. The radA100 mutation sensitized stationary phase cells to X-rays if they had been grown in glucose-supplemented rich medium, but not if they had been grown in nonsupplemented rich medium (indicating a defect in glucose-induced resistance). Similarly, logarithmic phase cells were sensitized to X-rays, UV radiation and methyl methanesulfonate if they had been grown in rich medium, but not if they had been grown in minimal medium (indicating a defect in medium-dependent resistance). Relative to the wild-type strain, the radA100 mutant was deficient in the repair of X-ray-induced DNA single-strand breaks when grown to log phase in rich medium, but not when grown in minimal medium. This is a novel mutation among the known DNA repair defects in that it did not sensitize log phase cells, grown in minimal medium, to X- or UV-radiation.