DNA repair in Proteus mirabilis. VI. Plasmid (R46-) mediated recovery and UV mutagenesis.

Summary The expression of plasmid R46-mediated recovery and mutagenic function (s) was studied in P. mirabilis, which is normally either weakly or nonmutable after UV exposure. The plasmid was found to confer on P. mirabilis enhanced UV resistance as well as UV-induced mutability for various types of forward mutations and reversion of the thr273 mutation. The plasmid enhanced survival of UV-irradiated phages in P. mirabilis both in unirradiated host cells and with increased efficiency after UV-exposure of host cells, as is characteristic of UV-inducible phage reactivation. Spontaneous mutability of P. mirabilis harboring R46 was about 2 to 7 times higher than that of cells without plasmid, depending on the marker, repair type, and plating density of the cells used. All of these R46-mediated rescue and mutagenic functions require the rec672⁺ gene function.It is assumed that the plasmid R46 adds functions to P. mirabilis comparable to those deficient in umuC and uvm mutants of E. coli (Kato and Shinoura, 1977; Steinborn, 1978) and that P. mirabilis possesses functions homologous to those controlled in E. coli by the recA⁺ and lexA⁺ genes.The significance of plasmid-mediated rescue and mutagenic functions for bacteria which lack the misrepair branch of mutagenesis, is discussed.