Identification of Closely Linked Loci Controlling Ultraviolet Sensitivity and Refractivity to Colicin E2 in Escherichia coli

Mutants (phenotypic symbol Ref-II) refractory to colicin E2 have been isolated in several strains of Escherichia coli K-12, and a refII locus has been mapped 1 to 2 min counter clockwise to thr. A small number of Ref-II mutants are also ultraviolet (UV)-sensitive and the uv(s) locus in one such strain has been mapped close to the refII locus near thr. The Ref-II mutation alone does not affect recombinant formation in F(-) strains, but the Ref-II, UV(s) strains behave in many respects like Rec(-) mutants, giving reduced recombination frequencies in crosses with male strains. It is suggested that the refII and uv(s) loci correspond to closely linked if not identical genes, concerned in some way in the activity of one or more deoxyribonucleases, and that the Ref-II, UV(s) mutants arise as the pleiotropic expression of a single gene or of a deletion or polar mutation affecting linked genes.