Escherichia coli DNA repair genes radA and sms are the same gene

Escherichia coli strains carrying radA100 or sms mutations were identical in their sensitivities to either methyl methanesulfonate or UV radiation treatment and in their plasmid complementation patterns for UV radiation survival. DNA sequencing analysis of the radA mutant and radA1 strains and comparison of their sequences with the published sms gene sequence showed the radA mutant to differ only by a G-to-A transition mutation, which is predicted to change a cysteine in a zinc-finger motif to tyrosine. The sms gene is concluded to be identical to the previously described radA gene. The radA100 mutation (named for its role in radiation re-sistance) was isolated because it made Escherichia coli cells sensitive to gamma radiation (3). This mutation maps close to the serB locus (3) and has been placed at 99.5 min on the E. coli K-12 linkage map (1). Log-phase radA mutant cells show in-creased sensitivity to X rays, methyl methanesulfonate (MMS), and UV radiation when grown in rich medium but not when grown in minimal medium (3). Rich medium-grown radA100 cells are also 30 % deficient in their ability to repair X-ray