Comparison of the Escherichia coli umu+-encoded function with plasmid R46-mediated error-prone repair in DNA-damaged cells.

Escherichia coli strain TK701 umu+ was more resistant than strain TK702 umu when tested against bleomycin (BLM), cis-platinum(II) diamminodichloride (PDD), ultraviolet light and methyl methanesulphonate (MMS), which produce single-strand DNA damage. However, the umu mutant was no more sensitive to mitomycin C (MTC) or proflavine (PF), which cause double-strand DNA binding. Strain TK702 umu was nonmutable by any of the agents, whereas mutations were induced in the wild-type strain by PDD, UV, MMS and MTC. The E. coli umu+ function therefore mimics plasmid R46-mediated error-prone repair in protecting only against single-strand DNA damage, whilst enhancing mutagenesis by both single- and double-strand damaging agents. Comparison of plasmid R46-mediated protection and mutagenesis in umu+ and umu strains indicated that the plasmid confers a greater error-prone DNA-repair activity in the mutant. Results are discussed in terms of analogy between host umu+ and plasmid muc+ functions.