AmpR is a master regulator of gene expression in P. aeruginosa PAO1.

AmpR positively regulates resistance to β-lactam antibiotics by upregulating expression of the amp genes, nagZ and downregulating creD. In addition, AmpR affects fluoroquinolone resistance by negatively regulating expression of mexT, the positive regulator of the MexEF-OprN efflux pump. Expression of the virulence and stress response sigma factor, RpoS and QS-regulated acute virulence factors is downregulated in PAOΔampR, indicating positive AmpR regulation. AmpR also negatively regulates biofilm formation via an unknown mechanism. AmpR modulates levels of the small RNA rsmZ, whose levels are lower in PAOΔampR with a corresponding enhanced expression of RsmA. Downregulation of some of the T3SS genes in the ampR mutant is possibly by regulating ptrB expression, via PrtR. Further, two major regulators of the alginate biosynthetic pathway, AlgT/U and AlgB are negatively regulated by AmpR, thereby potentially also regulating alginate production. Whether these AmpR interactions are direct or indirect needs to be investigated.