Mycobacterium smegmatis RNA polymerase: DNA supercoiling, action of rifampicin and mechanism of rifampicin resistance

Mol Microbiol. 1993 Apr;8(2):277-85. doi: 10.1111/j.1365-2958.1993.tb01572.x.


We have isolated RNA polymerase from Mycobacterium smegmatis and established conditions for specific transcription initiation in vitro. The M. smegmatis enzyme has a strong dependence on supercoiling of the DNA substrate for transcription from mycobacterial promoters. We also show that RNA polymerase is the target for rifampicin, and that this antibiotic specifically inhibits the transition from synthesis of short oligoribonucleotides to full-length transcripts. RNA polymerase isolated from a rifampicin-resistant mutant of M. smegmatis is less sensitive to rifampicin in vitro, confirming that one mechanism of rifampicin resistance in mycobacteria is through alteration of RNA polymerase. This in vitro transcription system provides a simple method for the characterization of gene expression in mycobacteria including the pathogens Mycobacterium tuberculosis, Mycobacterium avium and Mycobacterium leprae. It also provides a system for evaluating potential anti-mycobacterial drugs.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Bacterial Proteins / antagonists & inhibitors
  • Bacterial Proteins / isolation & purification
  • Bacterial Proteins / metabolism*
  • DNA, Bacterial / genetics*
  • DNA, Superhelical / genetics*
  • DNA-Directed RNA Polymerases / antagonists & inhibitors
  • DNA-Directed RNA Polymerases / isolation & purification
  • DNA-Directed RNA Polymerases / metabolism*
  • Drug Resistance, Microbial
  • Heat-Shock Proteins / metabolism
  • Mycobacterium / drug effects
  • Mycobacterium / enzymology*
  • Mycobacterium / genetics
  • Promoter Regions, Genetic
  • Rifampin / pharmacology*
  • Substrate Specificity
  • Transcription, Genetic


  • Bacterial Proteins
  • DNA, Bacterial
  • DNA, Superhelical
  • Heat-Shock Proteins
  • DNA-Directed RNA Polymerases
  • Rifampin