Protein Domain : ArsR-type transcription regulator, HTH motif IPR018334

Type	Conserved_site
Description	Bacterial transcription regulatory proteins that bind DNA via a helix-turn-helix (HTH) motif can be grouped into families on the basis of sequence similarities. One such group, termed arsR, includes several proteins that appear to dissociate from DNA in the presence of metal ions: arsR, which functions as a transcriptional repressor of an arsenic resistance operon; smtB from Synechococcus sp. (strain PCC 7942), which acts as a transcriptional repressor of the smtA gene that codes for a metallothionein; cadC, a transcription regulator of the cadmium resistance (cad) operon which encodes a Cd/Pb-specific efflux ATPase [].The HTH motif is thought to be located in the central part of these proteins [ ]. The motif is characterised by a number of well-conserved residues: at its N-terminal extremity is a cysteine residue; a second Cys is found in arsR and cadC, but not in smtA; and at the C terminus lie one or two histidines. These residues may be involved in metal-binding (Zn in smtB; metal-oxyanions such as arsenite, antimonite and arsenate for arsR; and cadmium for cadC) []. It is believed that binding of a metal ion could induce a conformational change that would prevent the protein from binding DNA [].
Short Name	ArsR_HTH