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Journal of Bacteriology, November 1999, p. 6876-6881, Vol. 181, No. 22
Institut für Mikrobiologie,
Martin-Luther-Universität Halle-Wittenberg, D-06099 Halle,
Germany
Received 13 July 1999/Accepted 31 August 1999
The Czc system of Ralstonia sp. strain CH34 mediates
resistance to cobalt, zinc, and cadmium through ion efflux catalyzed by
the CzcCB2A cation-proton antiporter. The CzcD protein is
involved in the regulation of the Czc system. It is a membrane-bound
protein with at least four transmembrane
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
CzcD Is a Heavy Metal Ion Transporter Involved in
Regulation of Heavy Metal Resistance in Ralstonia sp.
Strain CH34
-helices and is a member of a subfamily of the cation diffusion facilitator (CDF) protein family,
which occurs in all three domains of life. The deletion of
czcD in a Ralstonia sp. led to partially
constitutive expression of the Czc system due to an increased
transcription of the structural czcCBA genes, both in the
absence and presence of inducers. The czcD deletion could
be fully complemented in trans by CzcD and two other CDF
proteins from Saccharomyces cerevisiae, ZRC1p and COT1p.
All three proteins mediated a small but significant resistance to
cobalt, zinc, and cadmium in Ralstonia, and this resistance was based on a reduced accumulation of the cations. Thus, CzcD appeared
to repress the Czc system by an export of the inducing cations.
*
Corresponding author. Mailing address: Institut
für Mikrobiologie, Martin-Luther-Universität
Halle-Wittenberg, Kurt-Mothes-Str. 3, D-06099 Halle, Germany. Phone:
(49)-345-5526352. Fax: (49)-345-5527010. E-mail:
d.nies{at}mikrobiologie.uni-halle.de.
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