ZntA is a cation-translocating ATPase which exports from Escherichia coli Cd(II) and Pb(II), as well as Zn(II). The metal-dependent ATP hydrolysis activity of purified ZntA was recently characterised and showed a specificity for Cd(II), Pb(II) and Zn(II). zntA expression has been reported to be up-regulated primarily by Zn(II), mediated by the regulatory protein ZntR, belonging to the MerR transcriptional regulator family. In contrast to previous claims, we now show, using a Φ(zntA-lacZ) monolysogen, that Cd(II) is the most effective inducer of zntA, which is also induced significantly by Pb(II). The Cd(II)- and Pb(II)-dependent transcriptional up-regulation of zntA is also mediated by ZntR.
