The mitochondrial inner membrane protein Lpe10p, a homologue of Mrs2p, is essential for magnesium homeostasis and group
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O R I GI N A L P A P E R
J. Gregan á D. M. Bui á R. Pillich á M. Fink G. Zsurka á R. J. Schweyen
The mitochondrial inner membrane protein Lpe10p, a homologue of Mrs2p, is essential for magnesium homeostasis and group II intron splicing in yeast Received: 14 April 2000 / Accepted: 20 August 2000 / Published online: 11 January 2001 Ó Springer-Verlag 2001
Abstract The yeast ORF YPL060w/LPE10 encodes a homologue of the mitochondrial protein Mrs2p. These two proteins are 32% identical, and have two transmembrane domains in their C-terminal regions and a putative magnesium transporter signature, 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 with both termini oriented towards the matrix space. Disruption of the LPE10 gene results in a growth defect on non-fermentable substrates (petite phenotype) and a marked defect in group II intron splicing. The fact that in intron-less strains lpe10 disruptants also exhibit a petite phenotype indicates that functions other than RNA splicing are aected by the absence of Lpe10p. In the mitochondria, concentrations of magnesium, but not of several other divalent metal ions, are increased when Lpe10p is overexpressed and reduced when it is absent. Magnesium concentrations are raised to normal levels and growth on non-fermentable substrates is partially restored by the expression of CorA, the bacterial magnesium transporter, in the lpe10 disruptant. These features are similar to those previously reported for Mrs2p, suggesting that Lpe10p and Mrs2p are functional homologues. However, they cannot easily substitute for each other. Their roles in magnesium homeostasis and, possibly as a secondary eect, in RNA splicing are discussed.
Communicated by T. D. Fox J. Gregan á D. M. Bui1 á R. Pillich á M. Fink á G. Zsurka R. J. Schweyen (&) Vienna Biocenter, Department of Microbiology and Genetics, University of Vienna, Dr. Bohrgasse 9, A-1030 Vienna, Austria E-mail: [email protected] Tel.: +43-1-4277-54604 Fax: +43-1-4277-9546 Present address: Intercell GmbH, Vienna Biocenter, Dr. Bohrgasse 9, A-1030, Vienna, Austria
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Key words Mitochondria á Magnesium homeostasis á Group II introns á Protein topology á CorA protein family
Introduction Expression and assembly of the few structural genes encoded by mitochondrial DNA requires an unexpectedly large number of nuclear gene products. These products ful®ll various functions in RNA modi®cation and processing, particularly splicing of group I and group II introns, protein synthesis, assembly, stabilization and degradation of protein complexes of the respiratory chain (for review, see Costanzo and Fox 1990; Grivell 1995). Information on nuclear gene products that facilitate group II intron excision from pre-mRNA is still scarce. One such factor in yeast, Mss116p, shows similarity to RNA helicases of the DEAD-box family (Seraphin et al. 1989), and extracts from cells overexpressing this protein exhibit an increase in ATP-dependent splicing of group II i
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