Characterisation of CadR from Pseudomonas aeruginosa: a Cd(II)-responsive MerR homologue

cadR from Pseudomonas aeruginosa encodes a transcriptional regulatory protein which responds to Cd(II)≫Zn(II)>Hg(II) at its cognate promoter PcadA. CadR will also act to induce transcription at the Escherichia coli ZntR cognate promoter, PzntA, however, the induction profile is altered to Hg(II)>Cd(II)>Zn(II). Two separate single base pair deletions within PzntA result in further alteration of relative specificity in metal-ion induction profile for CadR. This demonstrates that the operator/promoter sequence can play a role in defining optimal ligand response and that for these regulators specificity is not solely a function of the regulatory protein.