Characterization of an Escherichia coli Mutant (radB101) Sensitive to γ and uv Radiation, and Methyl Methanesulfonate

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Abstract
After N-methyl-N′-nitro-N-nitrosoguanidine mutagenesis of Escherichia coli K-12 (xthA14), an 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 wild-type cells to γ and uv radiation, and to methyl methanesulfonate. When known DNA repair-deficient mutants were ranked for their γ-radiation sensitivity relative to their uv-radiation sensitivity, their order was (starting with the most selectively γ-radiation-sensitive strain): recB21, radB101, wild type, polA1, recF143, lexA101, recA56, uvrD3, and uvrA6. The radB mutant was normal for γ- and uv-radiation mutagenesis, it showed only a slight enhancement of γ- and uv-radiation-induced DNA degradation, and it was ∼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 γ irradiation and in postreplication repair after uv irradiation for the following reasons: the radB strain was normal for the host-cell reactivation of γ- and uv-irradiated bacteriophage λ; the radB mutation did not sensitize a recA strain, but did sensitize a polA strain to γ and uv radiation; the radB mutation sensitized a uvrB strain to uv radiation.