A conditional antimutator in E. coli.

A pleiotropic mutation in the purB gene of E. coli is described which lowers the spontaneous mutation frequency of other genes. The antimutator effect is very large for some genetic loci, but is absent at other sites. Both forward and reverse mutations are affected. This mutation in purB is temperature sensitive for both adenine auxotrophy and the antimutator action. Adenine, or adenosine, or low temperature growth abolish the antimutator effect. The mutagenicity of base analogs and nitrosoguanidine at several loci was found to be reduced by this purB mutation. The antimutator effect is recessive in strains merodiploid for the purB region. The frequency of reversion of mutation on F' episomes is affected by the chromosomal antimutator, which therefore acts in trans. Xray and UV sensitivity are normal in this mutant, which is the first antimutator characterized in E. coli.