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PLoS Genet. 2014 Jun 26;10(6):e1004429. doi: 10.1371/journal.pgen.1004429. eCollection 2014 Jun.

Transport of magnesium by a bacterial Nramp-related gene.

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The University of Maryland, Department of Cell Biology and Molecular Genetics, College Park, Maryland, United States of America.
The University of Texas Southwestern Medical Center, Department of Biochemistry, Dallas, Texas, United States of America.
Sanford-Burnham Medical Research Institute, La Jolla, California, United States of America; A.A.Kharkevich Institute for Information Transmission Problems, Russian Academy of Sciences, Moscow, Russia.
Virginia Tech University, Department of Biological Systems Engineering, Blacksburg, Virginia, United States of America.


Magnesium is an essential divalent metal that serves many cellular functions. While most divalent cations are maintained at relatively low intracellular concentrations, magnesium is maintained at a higher level (∼0.5-2.0 mM). Three families of transport proteins were previously identified for magnesium import: CorA, MgtE, and MgtA/MgtB P-type ATPases. In the current study, we find that expression of a bacterial protein unrelated to these transporters can fully restore growth to a bacterial mutant that lacks known magnesium transporters, suggesting it is a new importer for magnesium. We demonstrate that this transport activity is likely to be specific rather than resulting from substrate promiscuity because the proteins are incapable of manganese import. This magnesium transport protein is distantly related to the Nramp family of proteins, which have been shown to transport divalent cations but have never been shown to recognize magnesium. We also find gene expression of the new magnesium transporter to be controlled by a magnesium-sensing riboswitch. Importantly, we find additional examples of riboswitch-regulated homologues, suggesting that they are a frequent occurrence in bacteria. Therefore, our aggregate data discover a new and perhaps broadly important path for magnesium import and highlight how identification of riboswitch RNAs can help shed light on new, and sometimes unexpected, functions of their downstream genes.

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