JB Accepts, published online ahead of print on 6 November 2009

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J. Bacteriol. doi:10.1128/JB.01239-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Promoter and riboswitch control of the Mg²⁺ transporter MgtA from Salmonella enterica

Michael J. Cromie and Eduardo A. Groisman^*

Howard Hughes Medical Institute, Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri, 63110, USA

^* To whom correspondence should be addressed. Email: groisman{at}borcim.wustl.edu.

The MgtA protein from Salmonella enterica serovar Typhimurium mediates Mg²⁺ uptake from the periplasm into the cytoplasm. Here we report that the PhoP/PhoQ two-component regulatory system, which responds to periplasmic Mg²⁺, governs mgtA transcription initiation at all investigated Mg²⁺ concentrations, and that the Mg²⁺-sensing 5' leader region of the mgtA gene controls transcription elongation into the mgtA coding region when Salmonella is grown in media with < 50 μM Mg²⁺. Overexpression of the Mg²⁺ transporter CorA, which is believed to increase cytoplasmic Mg²⁺ levels, decreased mgtA transcription in a manner dependent on a functional mgtA 5' leader.