Metal-binding repressor for the cad operon. Involved in resistance to heavy metals, such as cadmium, bismuth, zinc or lead. Binds 2 metal ions per subunit. Metal binding to the N-terminal regulatory site causes the repressor to dissociate from the DNA. Homodimer. The N-terminal, regulatory metal binding site 1 has higher affinity for cadmium than for zinc. The second metal binding site has higher affinity for zinc and has no regulatory function.