Escherichia coli Cells Exposed to Streptomycin Display a Mutator Phenotype

Mistranslation mediated by the mutA and mutC tRNA alleles elicits a strong mutator phenotype (H. S. Murphy and M. Z. Humayun, J. Bacteriol. 179:7507–7514, 1997; M. M. Slupska, C. Baikalov, R. Lloyd, and J. H. Miller, Proc. Natl. Acad. Sci. USA 93:4380–4385, 1996). Here, we show that exposure to streptomycin, an antibiotic known to promote mistranslation, induces a recA- and umuDC-independent mutator phenotype detected as enhanced mutagenesis at a 3,N(4)-ethenocytosine lesion borne on transfected M13 single-stranded DNA.