title: Genetic studies on the beta subunit of Escherichia coli RNA polymerase. III. Analysis of low-level rifampicin-resistant mutants.
abstract: Spontaneously-occurring rifampicin-resistant mutants that survive on low (20 micrograms ml-1) but not high drug concentrations (200 micrograms ml-1) have been isolated. One such mutation appears to map close to residue 650 on the beta 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.
mesh_terms: D012321:DNA-Directed RNA Polymerases / Q000235:genetics*; D004352:Drug Resistance, Microbial; D004926:Escherichia coli / Q000235:genetics*; D007700:Kinetics; D046911:Macromolecular Substances; D009154:Mutation; D011485:Protein Binding; D012293:Rifampin / Q000494:pharmacology
chemical_list: D046911:Macromolecular Substances; D012321:DNA-Directed RNA Polymerases; D012293:Rifampin