Cellular Adaptations to Cytoplasmic Mg<sup>2+</sup> Limitation
Eduardo A. Groisman, Carissa Chan
Abstract
Mg 2+ is the most abundant divalent cation in living cells. It is essential for charge neutralization, macromolecule stabilization, and the assembly and activity of ribosomes and as a cofactor for enzymatic reactions. When experiencing low cytoplasmic Mg 2+ , bacteria adopt two main strategies: They increase the abundance and activity of Mg 2+ importers and decrease the abundance of Mg 2+ -chelating ATP and rRNA. These changes reduce regulated proteolysis by ATP-dependent proteases and protein synthesis in a systemic fashion. In many bacterial species, the transcriptional regulator PhoP controls expression of proteins mediating these changes. The 5′ leader region of some mRNAs responds to low cytoplasmic Mg 2+ or to disruptions in translation of open reading frames in the leader regions by furthering expression of the associated coding regions, which specify proteins mediating survival when the cytoplasmic Mg 2+ concentration is low. Microbial species often utilize similar adaptation strategies to cope with low cytoplasmic Mg 2+ despite relying on different genes to do so.