Inhibition of transcription and translation of an arginine-induced and rifampin-induced acetylornithine delta-transaminase of Escherichia coli

Evidence that rifampicin can stimulate readthrough of transcriptional terminators in Escherichia coli, including the attenuator of the rpoBC operon

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.

Alteration of regulation of arginine biosynthesis in Escherichia coli W by mutation to rifampin resistance

The synthesis of acetylornithine delta-transaminase is induced by arginine and by rifampin in an arginine-inducible mutant of Escherichia coli W. A mutant of the arginine-inducible strain was isolated which is resistant to rifampin. The mutation which has brought about rifampin resistance has altered RNA polymerase and has simultaneously altered the regulation of arginine biosynthesis. Three of the enzymes of arginine biosynthesis, acetylornithinase, ornithine transcarbamylase, and argininosuccinase, show a greater rate of derepression and a 2--12-fold higher level of enzyme activity in the rifampin-resistant mutant than in the parent arginine-inducible strain. Acetylornithine delta-transaminase is no longer inducible by rifampin alone, and the level of inducibility by arginine plus rifampin has been reduced by 70%. The results indicate that RNA polymerase is involved in regulation of arginine biosynthesis in E. coli W.