FIGURE 7.

Proposed model of MpfA function in high Mg²⁺ medium. Mg²⁺ ions are represented as dots and the amount of dots corresponds to the concentration. The arrows represent the direction of Mg²⁺ transport, and we propose that MpfA (SA0657) is a Mg²⁺ exporter (or at least an essential component of one). In a WT strain (Left) internal Mg²⁺ concentration is maintained lower than the external one by the combined action of Mg²⁺ importers (MgtE/CorA) and MpfA. MpfA activity is potentially regulated by Mg²⁺ internal concentration, through binding of Mg²⁺ at the CBS pair. In absence of MpfA (Right), Mg²⁺ cannot be exported anymore leading to an increase in internal Mg²⁺ up to toxic concentration. This toxicity could for example manifest itself in modified RNA structures, where higher Mg²⁺ leads to more stable RNA double helices.