Close-up view of the regulatory metal binding sites of E. coli ZntR (A), S. coelicolor Zur(B), S. aureus CzrA (C), and S. pneumoniae AdcR (D). Note that three of the four Zn(II) regulators harbor two metal binding sites that are within 10 Å of one another, either as part of a binuclear metal center consisting of two shared ligands, as in E. coli ZntR (panel A) [18] or in an amino acid sequence as is the case in S. coelicolor Zur [65,66] and S. pneumoniae AdcR [67] in panels B and D, respectively.