R Factor-mediated Resistance to Ultraviolet Light in Strains of Escherichia coli Deficient in Known Repair Functions

Abstract

The expression of resistance to UV irradiation mediated by R factor R46 was studied in strains deficient in excision repair and recombination repair. The R factor protected wild-type bacteria and wild-type cells in which repair was inhibited by the substitution of bromouracil for chromosomal thymine. It increased the survival of strains defective in the endonucleolytic (uvr), repolymerizing (pol) and joining (lig) stages of the excision repair process. Recombination deficient mutants of recB or recC loci were protected by R46, but the R factor had little effect on the survival of a recA strain or a recA recB double mutant. R46 increased the survival of cells that were treated with chloramphenicol before UV irradiation, but did not protect cultures treated with chloramphenicol after irradiation. R46 apparently confers resistance to the lethal effects of UV irradiation by a mechanism that is independent of excision repair. Resistance may be mediated by an inducible gene product, which is possibly a nuclease and dependent on a functional host recA gene for expression.