Escherichia coli merodiploids with altered ratios of episomal to chromosomal RNA polymerase activity

Summary Starting with an E. coli merodiploid strain (rpoB ⁺ (rifS)/rpoB^- (rifR)) containing equal amounts of rifampicin-sensitive and resistant RNA polymerase activities, mutants were isolated that had a disproportionately high ratio of the rifampicin-resistant enzyme activity. With one strain it is shown that the mutation responsible for this phenotype is closely linked to the rifR (rpoB^-) allele.