Separate mechanisms are involved in rifampicin upmodulated and downmodulated gene expression in Salmonella Typhimurium

Sub-MIC antibiotics differentially modulate transcription of subsets of genes by unknown mechanisms. Paradoxically, the RNA polymerase inhibitor rifampicin is able to both upmodulate as well as downmodulate transcription when present at sub-MIC levels. In this study, we analyzed DNA sequences required for transcription modulation. For three downmodulated promoters, the necessary sequences were within those contacted by the RNA polymerase during transcription initiation. Thus hypersensitivity is a characteristic of the RNA polymerase promoter complexes. The sequences needed for upmodulation included both upstream and downstream sequences in one case, only upstream sequences for another promoter and only downstream sequences for the third. Thus, there appear to be multiple mechanisms of transcription modulation by rifampicin.