Molecular mechanism of MexR-mediated regulation of MexAB-OprM efflux pump expression in Pseudomonas aeruginosa

To elucidate the molecular mechanism by which the MexR repressor regulates expression of the MexAB-OprM efflux pump, we investigated MexR and the mexR -mexA intergenic DNA (mexOP) interaction. and transcription of the mexA-lac Z reporter gene containing different lengths or mexOP. Homogeneously purifi ed MexR bound specifically to mexOP proximal to mexR. The mexOP-lacZ fusion gene lacking the region immediately proximal to mexR showed minimum enzyme activity, thereby suggesting that a promoter element is located between me xR and the MexR-binding sires. These observations explain the mechanism of self-regulation of mexR expression as well as low and elevated expression o f MexAB-OprM in the wild-type strain and nalB-type mutant, respectively, of Pseudomonas aeruginosa. (C) 2001 Federation of European Microbiological So cieties. Published by Elsevier Science B.V. All rights reserved.