The bacterial magnesium transporter CorA can functionally substitute for its putative homologue Mrs2p in the yeast inner mitochondrial membrane

The yeast nuclear gene MRS2 encodes a protein of 54 kDa, the presence of wh ich has been shown to be essential for the splicing of group II intron RNA in mitochondria and, independently, for the maintenance of a functional res piratory system. Here we show that the MRS2 gene product (Mrs2p) is an inte gral protein of the inner mitochondrial membrane. It appears to be inserted into this membrane by virtue of two neighboring membrane spanning domains in its carboxyl-terminal half. A large amino-terminal and a shorter carboxy l-terminal part are likely to be exposed to the matrix space. Structural fe atures and a short sequence motif indicate that Mrs2p may be related to the bacterial CorA Mg2+ transporter. In fact, overexpression of the CorA gene in yeast partially suppresses the pet(-) phenotype of an mrs2 disrupted yea st strain. Disruption of the MRS2 gene leads to a significant decrease in t otal magnesium content of mitochondria which is compensated for by the over expression of the CorA gene. Mutants lacking or overproducing Mrs2p exhibit phenotypes consistent with the involvement of Mrs2p in mitochondrial Mg2homeostasis.