Rifampicin Resistance of RNA Polymerase in the Binary Complex with DNA

Addition of rifampicin to a preincubated mixture of RNA polymerase and DNA does not lead to inhibition of the subsequent initiation of RNA chain synthesis. The formation of the enzymatically active binary complex between RNA polymerase and DNA, however, proved to be very sensitive to the action of the inhibitor. Once the complex has formed in the absence of substrate the enzyme is resistant to the antibiotic. The presence of sigma factor is not required for the formation of the resistant complex. In the presence of sigma, however, more resistant complex is formed between enzyme and DNA containing sigma specific initiation sites. The binary complex between RNA polymerase containing sigma factor and sigma specific DNA is more rapidly inactivated during prolonged incubation with rifampicin than a complex formed with unspecific DNA or in the absence of sigma. Rifampicin may therefore be used as a tool to discriminate sigma specific and unspecific active complexes of RNA polymerase and template.