Properties of R-plasmid pEB017, which confers both enhanced UV-radiation resistance and mutability to wild-type, recA and umuC strains of Escherichia coli K12

Abstract

The R-plasmid, pEB017, restored recombination ability to recA56 and conferred enhanced resistance to UV-radiation and enhanced UV-radiation mutability to wild-type, recA56 and umuC36 strains of Escherichia coli K12. Comparatively, pEB017 enhanced UV-radiation mutability in a umuC strain, and also enhanced UV-radiation and nitrofuran mutability in a wild-type strain several-fold more than did another R-plasmid, pKM101. Plasmid pEB017 also mediated about a 3-fold enhancement of the SOS induction of beta-galactosidase synthesis in a recA strain, compared with the normal recA+ gene of E. coli. A BamHI fragment of pEB017 DNA was cloned into plasmid vector pBR322 to yield pEB021. The BamHI fragment in pEB021 (3.5 kb) is about 170 bp longer between the BamHI and PstI sites on the left end of the recA-like fragment, compared with published data on a similarly cloned recA gene from E. coli. Plasmid pEB021 conferred enhanced resistance to UV-radiation and enhanced UV-radiation mutability in wild-type and recA strains, and restored recombination ability in a recA strain. The introduction of pEB021 into a umuC strain made the cells slightly more resistant to killing by UV-irradiation, and promoted a small amount of UV-mutability in an otherwise nonmutable strain. These results suggest that R-plasmid pEB017 has a recA-like gene that mediates the enhanced resistance to UV-radiation and enhanced UV-radiation mutability, but which seems different in several important aspects from the normal recA gene in E. coli.