The rex genes of lambda prophage modify ultraviolet light and N-methyl-N-nitrosourea-induced responses to DNA damage in Escherichia coli.

Inactivation and mutagenesis of Escherichia coli by ultraviolet light and N-methyl-N-nitrosourea (MNU) were examined in isogenic strains that were (i) free of lambda phage, (ii) lysogenic for lambda or (iii) contained the lambda rexAB operon on a plasmid (prex20). Inactivation was enhanced when rex genes were present and this enhancement was greater for MNU than for UV. Mutagenesis was not greatly affected by the presence of the rex genes with one exception; UV-induced glnU degrees suppressor mutations were reduced in the strain harboring prex20. Control experiments using a strain containing only plasmid pACYC184 showed no effect on inactivation. A small depression in UV-induced mutagenesis was observed, however. These data suggest that the lambda RexAB proteins interfere with processes necessary for recovery from DNA damage and for fixation of one example of UV-induced mutation. This and other recent observations of effects by rex genes are discussed.