Compensatory Mutation

A compensatory mutation mitigates the genetic disadvantage of another mutation. The streptomycin resistance gene in Salmonella or E. coli endows the cells with great selective advantage on streptomycin media, but under conditions where the antibiotic is not present the primary mutants are disadvantaged because of the modified ribosomes (conveying the resistance) are less efficient in translation. Several passages through streptomycin-free media. the fitness of the bacteria improves without reversion to the wild type gene. The improvement is generally due to mutations that compensate for the shortcoming of the ribosome. fitness, reversion, second site reversion; Guan Y et al 2001 J Virology 75:11920; Kulathinal RJ et al 2004 Science 306:1553.