Involved in the induction of the mtrCDE-encoded efflux pump (PubMed:10417654). Binds specifically to the mtrCDE promoter region (PubMed:23221802). Required for high-level inducible resistance to the detergent Triton X-100 (TX-100) and the spermicide nonoxynol-9 (N-9) (PubMed:10417654). The affinity for the mtrCDE promoter increases 2-fold in the presence of TX-100, a known effector and substrate of the MtrCDE pump. The MtrA and MtrR-binding sites are sterically close and addition of an effector increases the affinity of MtrA for the mtrCDE promoter such that MtrR binding is negatively impacted.