A transcriptional regulator of the MerR family encoded by Bordetella pertussis was characterized in Escherichia coli and in vitro. Uniquely, the regulator responded specifically to Zn(II), Cd(II), and Co(II) and was named ZccR. Gel shift assays confirmed that ZccR binds to an adjacent divergent promoter possessing an elongated spacer region of 19 bp between the -10 and -35 elements, and that Zn(ll), Co(ll), and Cd(ll) reduced the protein affinity for DNA. Site-directed mutagenesis of four cysteine and six histidine residues of ZccR showed that the cysteine residues at positions 77, 112, and 122, conserved in many of the metal-responsive MerR-like regulators, were essential for induction. Mutagenesis of the histidine residues (positions 73, 87, 90, 126, 140, and 142) revealed that histidine residues at 90, 140, and 142 were required for full induction by all three metals. (C) 2003 Elsevier Science (USA). All rights reserved.