Modulation of allele leakiness and adaptive mutability in Escherichia coli

It is shown that partial phenotypic suppression of two ochre mutations ( ar gE3 and lacZU118) and an amber mutation tin argE) by sublethal concentratio ns of streptomycin in an rpsL(+) (streptomycin-sensitive) derivative of the Escherichia coli strain AB1157 greatly enhances their adaptive mutability under selection. Streptomycin also increases adaptive mutability brought ab out by the ppm mutation described earlier. Inactivation of recA affects nei ther phenotypic suppression by streptomycin nor replication-associated muta genesis but abolishes adaptive mutagenesis. These results indicate a causal relationship between allele leakiness and adaptive mutability.