Evidence that rifampicin can stimulate readthrough of transcriptional terminators inEscherichia coli,including the attenuator of therpoBCoperon

The genes encoding the beta and beta' subunits of RNA polymerase in E.coli, rpoB and rpoC, lie downstream of at least two ribosomal protein genes, rplJ (encoding L10) and rplL (L7/12), in a common operon. All four genes are served by promoter PL10, and an attenuator (partial terminator) of transcription, t1, lies between rplJL and rpoBC. Treatment of E.coli with rifampicin, under conditions producing partial inhibition of general RNA synthesis, can stimulate transcription of rpoBC. We have investigated the locus of this effect by fusing PL10 and t1 separately to galK, in suitable plasmids. Our studies of these fusions, and similar fusions involving transcriptional terminators derived from coliphage T7, indicate that low concentrations of rifampicin cause increased readthrough of several different transcriptional terminators in E.coli in vivo, including rpo t1. We discuss whether or not this unspecific mechanism is solely responsible for the observed stimulatory effects of the drug on rpoBC transcription.