Regulation of the Alr1 transporter by Mg supply

Magnesium is required for many essential processes and pathways, including protein synthesis and energy metabolism. In the yeast Saccharomyces cerevisiae, Mg2+ uptake across the plasma membrane primarily occurs via the magnesium transporter Alr1. Preliminary data had shown that Alr1-HA accumulation was decreased by Mg. Here I show that the epitope tag was responsible for this differential accumulation of Alr1, as native or N-terminally tagged Alr1 displayed much less differential accumulation. Immunoblotting and Ni2+ uptake assays indicated that both Mg-deficiency and the mnr2 mutation increased Alr1 activity, but under conditions where native protein accumulation was little affected. Since Mg-dependent regulation of Alr system activity and Alr1 protein accumulation did not correlate, I investigated the importance of the post-translational modification of Alr1 to regulation. These studies suggested that the post-translational modification of Alr1 and the C-terminal domain of the protein may be important for regulation