Genetic studies on the β subunit of Escherichia coli RNA polymerase

Abstract

Spontaneously-occurring rifampicin-resistant mutants that survive on low (20 μg ml^-1) but not high drug concentrations (200 μg ml^-1) have been isolated. One such mutation appears to map close to residue 650 on the β structural gene. RNA polymerase from low-level resistant strains shows an intermediate response to rifampicin in vitro: both the association and dissociation rates of the antibiotic are markedly reduced. Continued expression of this unusual phenotype upon introduction of a high-level resistance allele is described in terms of DNA blockade.