Identification of plasmid (pKM101)-coded proteins involved in mutagenesis and UV resistance.

Abstract

Mutagenesis of Escherichia coli by UV and many chemicals is not a passive process and requires the intervention of host functions. The isolation of chromosomal umuC mutants, which are nonmutable by many DNA-damaging agents and are slightly sensitive to them, has led to the model that the umuC gene product(s) functions in a pathway of ‘error-prone repair’1–3. UmuC mutants are suppressed by the introduction of the plasmid pKM1014; pKM101 was derived from the clinically isolated plasmid R46 by in vivo manipulations5. The muc (mutagenesis, UV and chemical) region of pKM101 is required for this suppression and we have suggested that it is an analogue of the chromosomal umuC gene(s)6. We have now subcloned the muc region onto the high-copy number vector pKB354 and identified two protein products by gel electrophoresis of maxicell preparations. Complementation analysis of muc insertion mutations has confirmed the existence of two genes, mucA and mucB, whose protein products are required for pKM101's effects on mutagenesis and resistance to killing. The molecular weights (MWs) of the mucA and mucB proteins are 16,000 and 45,000 respectively.