FIG 1.

Schematic representation of the known regulatory pathways for expression of the AcrAB-TolC efflux pump in Salmonella. The genes are represented as arrows, and their translated proteins are represented as ovals (transcriptional repressors) and hexagons (transcriptional activators). The AcrAB-TolC pump extrudes drugs across the cytoplasmic and outer membranes. Excessive production of AcrA and AcrB is prevented by the local repressor AcrR. Activation of acrA, acrB, and tolC transcription occurs primarily due to the global regulatory protein RamA by binding to the rambox upstream of these genes. As demonstrated, the regulatory proteins SoxS and Rob can also activate acrAB-tolC transcription. RamA expression is controlled by RamR, which represses the activation of ramA. Likewise, SoxR controls the expression of both soxR and soxS.