Helix-Turn-Helix DNA binding domain of putative Heavy Metal Resistance transcription regulators
Putative helix-turn-helix (HTH) heavy metal resistance transcription regulators (HMRTR), unknown subgroup. Based on sequence similarity, these proteins are predicted to function as transcription regulators that mediate responses to heavy metal stress in eubacteria. They belong to the MerR superfamily of transcription regulators that promote transcription of various stress regulons by reconfiguring the operator sequence located between the -35 and -10 promoter elements. A typical MerR regulator is comprised of two distinct domains that harbor the regulatory (effector-binding) site and the active (DNA-binding) site. Their N-terminal domains are homologous and contain a DNA-binding winged HTH motif, while the C-terminal domains are often dissimilar and bind specific coactivator molecules, such as, metal ions, drugs, and organic substrates. This subgroup lacks one of the conserved, metal-binding cysteines seen in the MerR1 group.