CueR (YbbI) of Escherichia coli is a MerR family regulator controlling expression of the copper exporter CopA

We have shown that the open reading frame ybbI in the genomic sequence of Escherichia coli K-12 encodes the regulator of expression of the copper-exporting ATPase, CopA. In vivo studies showed that ybbI (designated cueR for copper export regulator gene) was required for copper tolerance during growth, that disruption of cueR caused loss of copA expression and that copA gene expression was regulated by cueR and by copper or silver ions. Expression of a lacZ reporter gene under the control of the copA promoter was approximately proportional to the concentration of cupric ions in the medium, but increased more rapidly in response to silver ion concentrations. The start of the copA transcript was located by primer extension mapping, and DNase I protection assays showed that the CueR protein binds in vitro to a dyad symmetrical sequence within a 19 bp spacer sequence in the copA promoter. CueR binding occurs in vitro in both the presence and the absence of RNA polymerase with or without copper ions present but, in the presence of CueR, RNA polymerase and copper ions, permanganate-sensitive transcription complexes were formed. CueR is predicted to have an N-terminal helix-turn-helix sequence and shows similarity to MerR family regulators.