Suppression of Ultraviolet Sensitivity in Escherichia coli uvr502 by the su58 Missense Suppressor

of thesu58 missense suppressor into the chromosome of theuvr502 mutant, either by mutation or by transduction, results in a marked increase of ultraviolet resistance of theuvr502 mutant. In theuvr + genetic background, thesu58 suppressor causes some decrease of ultraviolet resistance and marked increase in the spontaneous mutation frequency. The presence of thesu58 suppressor did not decrease the high frequency of spontaneous mutants in the population of theuvr502 strain. However, the significant increase in spontaneous mutant frequency in theuvr + su58 strain makes the difference between theuvr502 su58 and theuvr + su58 strains 18 times lower than that between theuvr502 and theuvr + suppressor-free strains. Since the missense suppressors act at the level of translation, the results suggest that the product of theuvr (502 ) gene is a protein.