Characterization of an Escherichia coli mutant (radB101) sensitive to gamma and uv radiation, and methyl methanesulfonate.

After N-methyl-N'-nitro-N-nitrosoguanidine mutagenesis of Escherichia coli K-12 (xthA14), and X-ray-sensitive mutant was isolated. This sensitivity is due to a mutation, radB101, which is located at 56.5 min on the E. coli K-12 linkage map. The radB101 mutation sensitized wildtype cells to gamma and uv radiation, and to methyl methanesulfonate. When known DNA repair-deficient mutants were ranked for their gamma-radiation sensitivity relative to their uv-radiation sensitivity, their order was (starting with the most selectively gamma-radiation-sensitive strain): recB21, radB101, wild type, polA1, recF143, lexA101, recA56, uvrD3, and uvrA6. The radB mutant was normal for gamma- and uv-radiation mutagenesis, it showed only a slight enhancement of gamma- and uv-radiation-induced DNA degradation, and it was approximately 60% deficient in recombination ability. The radB gene is suggested to play a role in the recA gene-dependent (Type III) repair of DNA single-strand breaks after gamma irradiation and in postreplication repair after uv irradiation for the following reasons; the radB strain was normal for the host-cell reactivation of gamma- and uv-irradiated bacteriophage lambda; the radB mutation did not sensitize a recA strain, but did sensitize a polA strain to gamma and uv radiation; the radB mutation sensitized a uvrB strain to uv radiation.