Differential mutagenicities of 6 N-nitroso-N-alkylurea derivatives in Escherichia coli strains with different DNA-repair capacities.

Reverse mutations to prototrophy by, and killing effects of, 6 N-nitroso-N-alkylurea derivatives such as NMU, NEU, NPU, NBU, NIBU and NAU were studied with E. coli strains H/r30R (wild-type), Hs30R (uvrA-), O16 (polA-) and NG30 (recA-). Both strains polA- and recA- were far more sensitive to killing by the 6-compounds than were the wild-type and uvrA- strains, and there was no difference in the sensitivity between the latter 2 strains. NMU was mutagenic in all 4 strains; wild-type, uvrA- and polA- strains were almost equally mutable but the compound was slightly mutagenic in the recA- strain. The other 5 compounds, NEU, NPU, NBU, NIBU and NAU, caused hardly any mutation in the recA- strain. NEU, NPU and NBU were equally mutagenic in the wild-type, uvrA- and polA- strains; however, NIBU and NAU were more mutagenic in the uvrA- than in the wild type or polA-. From the differential mutagenicities and lethalities induced by the 6 N-nitroso-N-alkylureas into the 4 tester strains, mutational patterns of the compounds can be classified into 3 types.