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Journal of Bacteriology, January 2008, p. 536-545, Vol. 190, No. 2
0021-9193/08/$08.00+0     doi:10.1128/JB.01481-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Characterization of the CopR Regulon of Lactococcus lactis IL1403

David Magnani, Olivier Barré, Simon D. Gerber, and Marc Solioz^*

Department of Clinical Pharmacology, University of Berne, Murtenstrasse 35, 3010 Berne, Switzerland

Received 13 September 2007/ Accepted 1 November 2007

To identify components of the copper homeostatic mechanism of Lactococcus lactis, we employed two-dimensional gel electrophoresis to detect changes in the proteome in response to copper. Three proteins upregulated by copper were identified: glyoxylase I (YaiA), a nitroreductase (YtjD), and lactate oxidase (LctO). The promoter regions of these genes feature cop boxes of consensus TACAnnTGTA, which are the binding site of CopY-type copper-responsive repressors. A genome-wide search for cop boxes revealed 28 such sequence motifs. They were tested by electrophoretic mobility shift assays for the interaction with purified CopR, the CopY-type repressor of L. lactis. Seven of the cop boxes interacted with CopR in a copper-sensitive manner. They were present in the promoter region of five genes, lctO, ytjD, copB, ydiD, and yahC; and two polycistronic operons, yahCD-yaiAB and copRZA. Induction of these genes by copper was confirmed by real-time quantitative PCR. The copRZA operon encodes the CopR repressor of the regulon; a copper chaperone, CopZ; and a putative copper ATPase, CopA. When expressed in Escherichia coli, the copRZA operon conferred copper resistance, suggesting that it functions in copper export from the cytoplasm. Other member genes of the CopR regulon may similarly be involved in copper metabolism.

Published ahead of print on 9 November 2007.

D.M. and O.B. contributed equally to this study.