The mitochondrial inner membrane protein Lpe10p, a homologue of Mrs2p, is essential for magnesium homeostasis and group II intron splicing in yeast

The yeast ORF YPL060w/LPE10 encodes a homologue of the mitochondrial protei n Mrs2p. These two proteins are 32%. identical, and have two transmembrane domains in their C-terminal regions and a putative magnesium transporter si gnature, Y/F-G-M-N, at the end of one of these domains. Data presented here indicate that Lpe10p is inserted into the inner mitochondrial membrane wit h both termini oriented towards the matrix space. Disruption of the LPE10 g ene results in a growth defect on non-fermentable substrates (petite phenot ype) and a marked defect in group II intron splicing. The fact that in intr on-less strains lpe10 disruptants also exhibit a petite phenotype indicates that functions other than RNA splicing are affected by the absence of Lpe1 0p. In the mitochondria, concentrations of magnesium, but not of several ot her divalent metal ions, are increased when Lpe10p is overexpressed and red uced when it is absent. Magnesium concentrations are raised to normal level s and growth on non-fermentable substrates is partially restored by the exp ression of CorA, the bacterial magnesium transporter, in the lpe10 disrupta nt. These features are similar to those previously reported for Mrs2p, sugg esting that Lpe10p and Mrs2p are functional homologues. However, they canno t easily substitute for each other. Their roles in magnesium homeostasis an d, possibly as a secondary effect, in RNA splicing are discussed.