Helix-Turn-Helix DNA binding domain of the CadR and PbrR transcription regulators
Helix-turn-helix (HTH) CadR and PbrR transcription regulators including Pseudomonas aeruginosa CadR and Ralstonia metallidurans PbrR that regulate expression of the cadmium and lead resistance operons, respectively. These proteins are comprised of distinct domains that harbor the regulatory (effector-binding) site and the active (DNA-binding) site. Their conserved N-terminal domains contain predicted winged HTH motifs that mediate DNA binding, while the C-terminal domains have three conserved cysteines which form a putative metal binding site. Some members in this group have a histidine-rich C-terminal extension. 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.