Different rifampin sensitivities of Escherichia coli and Mycobacterium tuberculosis RNA polymerases are not explained by the difference in the beta-subunit rifampin regions I and II.

Mycobacterium tuberculosis RNA polymerase is 1,000-fold more sensitive to rifampin than Escherichia coli RNA polymerase. Chimeric E. coli RNA polymerase in which the beta-subunit segment encompassing rifampin regions I and II (amino acids [aa] 463 through 590) was replaced with the corresponding region from M. tuberculosis (aa 382 through 509) did not show an increased sensitivity to the antibiotic. Thus, the difference in amino acid sequence between the rifampin regions I and II of the two species does not account for the difference in rifampin sensitivity of the two polymerases.