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

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Abstract
Partially diploid strains of Escherichia coli containing both rifampicin‐sensitive and rifampicin‐resistant RNA polymerase are, in general, sensitive to the drug: of the two 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. I show that 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.