Regulation of the operon responsible for broad-spectrum mercury resistance inStreptomyces lividans 1326

Publisher Website
Google Scholar
Abstract
The broad-spectrum mercury resistance ofStreptomyces lividans 1326 is mediated by six open reading frames (orf). These are arranged in two divergently transcribed operons. Theorfs merA (mercuric reductase) andmerB (organolyase) form one of the two operons. These genes and their regulation were further studied by deletion analysis and transcriptional fusion to the reporter genexylE in the plasmid pXE4. An increase in XylE activity in response to the presence of mercuric ions was observed. The function of ORF2 (MerT) and ORF3 (MerP) as mercury-specific transport proteins, previously postulated based on the structural features of the predicted proteins, was confirmed. Transcription of themer genes starts within the intercistronic region and two divergent promoters were identified by S1 nuclease mapping. Expression of the genes was negatively regulated by the product oforf1, now calledmerR. The repressor function was confirmed by gel retardation assays. MerR, produced inEscherichia coli, bound to two sites (operators) in the fragment containing the promoter region betweenmerA andmerR. Addition of mercuric ions and phenylmercuric acetate prevented the binding of MerR.