Actions of the rifamycins.

Correlation between rifampicin-resistance of slow-growing Rhizobium strains and their ability to express nitrogenase activity in culture

“…We do not know the basis of the rifampicin-resistance of the Rhizobium strains which were able to express nitrogenase activity in culture. Rifampicin-resistance may be a consequence of cell permeability to the drug and/or an altered RNA polymerase structure [9,14,15]. A role for RNA polymerase in the differentiation of nitrogen-fixing bacteroids has been inferred from the observation that several rifampicin-resistant mutants of both slow-and fast-growing Rhizohium strains form ineffective nodulus [8,16].…”

“…During the course of studies on the cowpea Rhizobium strain 32H 1 which expresses nitrogenase activity in culture [3], we noted that it grew on mannitol-salts-yeast extract (M +) medium [8] containing 500 /~g/ml rifampicin, an inhibitor of bacterial RNA polymerase [9]. This level of rifampicin-resistance was significantly higher than values reported for some other slow-and fastgrowing Rhizobium strains [8].…”

Ribonucleic Acid Synthesis in Plant Mitochondria: Effects of Some Inhibitors and Cyclic Nucleotides

“…This inhibition does not respond to the action of cAMP and cGMP under any of the conditions investigated. The synthesis is also highly sensitive to rifampicin, which is a specific inhibitor of RNA polymerase responsible for DNAdependent RNA synthesis (Wehrli and Staehelin 1971). The inhibition by rifampicin can partially be released, if the synthetic system is preincubated for 15 min with cAMP before the addition of the antibiotic.…”

Synthesis of RNA byRhodomicrobium vannieliiswarmer cells

“…1). As rifampicin is a specific inhibitor of the initiation of transcription, the target of the antibiotic being the fl subunit of the DNA-dependent RNA polymerase [12], the data indicated that de novo RNA synthesis was required for the maintenance of protein synthesis in dark anaerobically-incubated swarmer cells• Protein synthesis dependent upon long-lived messenger RNA would not have been inhibited in this way.…”