Evidence that pretreatment of Escherichia coli cells with N-methyl-N'-nitro-N-nitrosoguanidine enhances mutability of subsequently infecting phage lambda.

Abstract

The frequency of mutations in λ is significantly higher for host cells of a rec+ or recA- strain pretreated with N-methyl-N′-nitro-N-nitrosoguanidine (NG) than for untreated control cells. Direct NG treatment of λDNA-injected host cells results in about tenfold higher mutation frequency in λ than NG treatment of host cells alone. Since mutability of λ is enhanced by UV preirradiation of host cells in the rec+ strain but not in the recA- strain, indirect NG mutagenesis is different in mechanism from indirect UV mutagenesis. It is concluded that NG mutagenesis in λ consists of at least two processes: induction of rec+-independent mutagenic activity in the host bacterium and production of rec+-independent mutational damage to intracellular λDNA.