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J. Bacteriol. doi:10.1128/JB.01851-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

The zinc-responsive regulator Zur controls a zinc uptake system and some ribosomal proteins in Streptomyces coelicolor A3(2)

Laboratory of Molecular Microbiology, School of Biological Sciences, and Institute of Microbiology, Seoul National University, Seoul 151-742, Korea; Department of Chemistry, Mokpo National University, Muan, Korea

^* To whom correspondence should be addressed. Email: jhroe{at}snu.ac.kr.

	Abstract

In various bacteria Zur, a zinc-specific regulator of Fur family, regulates genes for zinc transport systems to maintain zinc homeostasis. It has also been suggested to control zinc mobilization by regulating some ribosomal proteins. The antibiotics-producing soil bacterium Streptomyces coelicolor contains four genes for Fur family regulators, and one (named as zur) is located downstream of the znuACB operon encoding a putative zinc uptake transporter. We found that zinc specifically repressed the level of znuA transcript, which was derepressed in zur mutant. Purified Zur, existing as homodimers, bound to the znuA promoter region in the presence of zinc, confirming the role of Zur as a zinc-responsive repressor. We analyzed transcripts for paralogous forms of ribosomal proteins L31 (rpmE1 and E2) and L33 (rpmG2 and G3) for their dependence on Zur, and found that RpmE2 and RpmG2 with no zinc-binding motif of conserved cysteines (C) are negatively regulated by Zur. C-negative RpmG3 and C-positive RpmE1 were not regulated by Zur. Instead, they were regulated by ^R as predicted from their promoter sequence. The rpmE1 and G3 were induced partially by EDTA in a manner dependent on ^R, suggesting that zinc-depletion could stimulate ^R regulatory system. This reflects a link between thiol-oxidizing stress and zinc-depletion. We determined the Zur binding sites within znuA and rpmG2 promoter regions by footprinting analyses and identified a consensus inverted repeat sequence (TGaaAatgatTttCA). This sequence matches closely with that for Mycobacterial Zur, and allows prediction of more genes in Zur regulon.

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