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J Bacteriol. 1971 November; 108(2): 737-741
Copyright © 1971 American Society for Microbiology. All Rights Reserved.

Mechanism of Action of Rifampin on Mycobacterium smegmatis

Research Laboratories, Gruppo Lepetit S.p.A., Milano, Italy

ABSTRACT

Deoxyribonucleic acid (DNA)-dependent ribonucleic acid (RNA) polymerase (EC 2.7.7.6) isolated from a rifampin-sensitive strain of Mycobacterium smegmatis was 90% inhibited by 1 µg of rifampin per ml; enzyme from a rifampin-resistant mutant was not affected by this concentration of antibiotic. Inhibition of phenylalanine-1-¹⁴C incorporation by rifampin in growing cultures was complete about 6 min after addition of antibiotic. Under the same conditions, uracil-2-¹⁴c incorporated was blocked after 1.5 to 2 min. Rifampin kills M. smegmatis very slowly. When rifampin-inhibited cultures were transferred to a rifampin-free medium, there was a partial resumption of uracil-2-¹⁴C incorporation, even in the presence of chloramphenicol. We conclude that a primary event in the inhibition of M. smegmatis by rifampin is the block of DNA-dependent RNA polymerase.

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