A recA-dependent mutator of Escherichia coli K12: method of isolation and initial characterization.

A number of mutator strains of E. coli were isolated using histochemical techniques which allow the identification of a single mutator colony on agar plates with as many as 2000 colonies. Several mutators isolated in this way were found by P1-mediated transduction to map to the proA--proB region of the E. coli chromosome. The map position of these mutators is very close to that of the conditional mutator, mutD. However, in contrast to mutD, one of these newly isolated mutators was suppressed in a thermosensitive recA strain at 43 degrees C, but not at 30 degrees C. This mutator mutation has been named mut-8. Besides being dependent upon recA, mut-8 is also dependent upon growth in enriched medium for the expression of its mutator activity. The mutator activity of mut-8 was found to be recessive to the wild-type allele.