The role of misrepair processes in the isolation of new types of streptomycin-resistant mutants in Escherichia coli.

Treatment of Escherichia coli cells with ethylmethanesulfonate followed by a prolonged delay for phenotypic expression allows to select new types of streptomycin-resistant mutants, which are double mutants with one change resulting from base mispairing and the second one from misrepair. The error-prone recA-dependent pathway is involved in this misrepair, as evidenced by the fact that recA strains do not provide double mutants.