Helix-Turn-Helix DNA binding domain of CueR-like transcription regulators
Helix-turn-helix (HTH) transcription regulators CueR and ActP, copper efflux regulators. In Bacillus subtilis, copper induced CueR regulates the copZA operon, preventing copper toxicity. In Rhizobium leguminosarum, ActP controls copper homeostasis; it detects cytoplasmic copper stress and activates transcription in response to increasing copper concentrations. These proteins are comprised of two distinct domains that harbor the regulatory (effector-binding) site and the active (DNA-binding) site. Their conserved N-terminal domains contain winged HTH motifs that mediate DNA binding, while the C-terminal domains have two conserved cysteines that define a monovalent copper ion binding site. These proteins share the N-terminal DNA binding domain with other transcription regulators of the MerR superfamily that promote transcription by reconfiguring the spacer between the -35 and -10 promoter elements.