Effects of the umuC36 mutation on ultraviolet-radiation-induced base-change and frameshift mutations in Escherichia coli.

The effects of the umuC36 mutation on the induction of base-change and frameshift mutations were studied. An active umuC gene was necessary in either the uvr+ strains of Escherichia coli K12 for UV- and X-ray-induced mutations to His+, ColER and SpcR, which are presumably base-change mutations, but it was not essential for ethyl methanesulphonate or N-methyl-N'-nitro-N-nitrosoguanidine-induced His+ mutations. In contrast, only 1 out of 13 trp- frameshift mutations examined was UV reversible, and the process of mutagenesis was umuC+-dependent, whereas a potent frameshift mutagen, ICR191, effectively induced Trp+ mutations in most of the strains regardless of the umu+ or umuC genetic background. These results suggest that base substitutions are a major mutational type derived from the umuC+-dependent pathway of error-prone repair.