Control of copper homeostasis in Escherichia coli by a P-type ATPase, CopA, and a MerR-like transcriptional activator, CopR

We have isolated and characterized a copper sensitive Escherichia coli muta nt that is deficient in the copper transporting P-type ATPase encoded by th e copA gene (previously ybaR). Measurements of uptake and efflux of Cu-64 b y wild-type and mutant cells implicated the CopA protein in copper efflux f rom the cytoplasm, and further demonstrated that cell-associated copper in intact E, coli cells is distributed between two kinetically distinguishable pools, the ratio of which was dramatically disturbed by the copA mutation. Using a copA-lacZ gene fusion the copA promoter was found to be specifical ly induced by copper, and this induction was shown to be dependent on a Mer R-like transcriptional activator encoded by a previously uncharacterized ge ne, copR (previously ybbI). In the copA deficient background the copA-lacZ fusion was super induced to very high levels even in the absence of copper addition to the medium, and this induction was dependent on CopR. These res ults indicated that the cytoplasmic copper concentration was dramatically i ncreased in the copA mutant, in agreement with the Cu-64 uptake experiments . Moreover, they implied, that the copper concentration in wild type cells is determined primarily by the CopA efflux pump, while copper is taken up b y an essentially constitutive mechanism. (C) 2000 Elsevier Science B.V. All rights reserved.