Isolation and Characterization of the nikR Gene Encoding a Nickel-Responsive Regulator in Escherichia coli

Expression of the nickel-specific transport system encoded by the Escherichia coli nikABCDE operon is repressed by a high concentration of nickel. By using random transposon Tn10 insertion, we isolated mutants in which expression of the nik operon became constitutive with respect to nickel. We have identified the corresponding nikR gene which encodes a nickel-responsive regulator. Expression of nikR was partially controlled by Fnr through transcription from the nikA promoter region. In addition, a specific transcription start site for the constitutive expression of nikR was found 51 bp upstream of the nikR gene.