On the Binding of Rifampicin to the DNA‐Directed RNA Polymerase from Escherichia coli

The capacity of RNA polymerase to bind the antibiotic rifampicin is rather sensitive to conditions which lead to conformational changes in the enzyme. Repeated freezing and thawing in 1 M LiCl as well as treatment with guanidinium chloride destroys the binding affinity of the enzyme for the inhibitor. Similarly rifampicin does not associate with any of the isolated subunits α, β or β′. Surprisingly, the reaction of an excess of mercurials with the enzyme leads only to a partial loss of binding capacity suggesting that –SH groups are not directly involved in the formation of the complex with rifampicin. During chain elongation very little rifampicin is bound to the enzyme. Simultaneously enzymatic activity is not affected by the inhibitor. RNA cannot protect the enzyme against the attachment of rifampicin although the binding capacity is reduced. Treatment of the complex of enzyme and antibiotic with RNA does not release rifampicin from the complex. These results support the hypothesis that the tight binding of rifampicin to RNA polymerase is the principal cause of the inhibitory action of the antibiotic.