Reversion of frameshift mutations by mutator genes in Escherichia coli.

The Escherichia coli mutator genes mutU4, mutS3, and mut-25 (a possible allele of mutL), previously known to induce transitional base changes, increased significantly the frequencies of reversion of lacZ frameshift mutations. mutT1, previously shown to induce only the transversion of adenine-thymine to cytosine-guanine, had no effect on the reversion of lacZ frameshift mutations. With mutator genes other than mutT1, small increases were found in the frequencies of reversion of trpA frameshift mutations.