DNA Blockade by Rifampicin‐Inactivated Escherichia coli RNA Polymerase, and Its Amelioration by a Specific Mutation

Abstract

Partially diploid strains of E. coli containing rifampicin-sensitive and rifampicin-resistant RNA polymerase [EC 2.7.7.6] are, in general, sensitive to the drug. Of the 2 copies of the rpoB gene present in such strains, that which codes for sensitive enzyme is dominant. RNA polymerase, purified from a normal sensitive strain of E. coli and inactivated by rifampicin, can blockade bacteriophage T7 DNA in vitro, inhibiting its transcription by drug-resistant enzyme molecules. A mutation, rcs-40, reverses the normal dominance relationship in vivo, without detectably affecting the concentrations of resistant and sensitive RNA polymerase in the diploid cell. rcs-40 is closely linked to the rpoB gene, which codes for the rifampicin-sensitive enzyme. Rifampicin-sensitive RNA polymerase purified from E. coli rcs-40, although indistinguishable from the normal enzyme by many criteria, is significantly less efficient in the production of drug-dependent DNA blockade.