The local repressor AcrR plays a modulating role in the regulation ofacrAB genes of Escherichia coliby global stress signals

摘要

SummaryGenesacrABencode a multidrug efflux pump inEscherichia coli. We have previously reported that transcription ofacrABis increased under general stress conditions (i.e. 4 ethanol, 0.5 M NaCl, and the stationary phase in Luria‐Bertanl medium). In this study,lacZtranscriptional fusions and anin vitrogel mobility shift assay have been utilized to study the mechanisms governing the regulation ofacrAB. We found that a closely linked gene,acrR, encoded a repressor ofacrAB. Nevertheless, the general stress conditions increased transcription ofacrABin the absence of functional AcrR, and such conditions surprisingly increased the transcription ofacrReven more strongly than that ofacrAB. These results suggest that the general‐stress‐induced transcription ofacrABis primarily mediated by global regulatory pathway(s), and that one major role of AcrR is to function as a specific secondary modulator to fine tune the level ofacrABtranscription and to prevent the unwanted overexpression ofacrAB. To our knowledge, this represents a novel mechanism of regulating gene expression inE. coli. Evidence also suggests that the up‐regulation ofacrABexpression under general stress conditions is not likely to be mediated by the known global regulators, such as MarA or SoxS, although elevated levels of these proteins were shown to increase the transcription