Transporter of the mitochondrial inner membrane that exports magnesium and thus, plays a key role in mitochondrial Mg(2+) homeostasis. Significantly increases steady-state mitochondrial magnesium concentration (PubMed:25585246). Rescues the group II RNA splicing defect in the MRS2 and LPE10 deletion mutants (PubMed:25585246). Present with 2060 molecules/cell in log phase SD medium. Belongs to the mitochondrial carrier (TC 2.A.29) family.