Fission yeast msp1 is a mitochondrial dynamin-related protein

We recently identified Msp1p, a fission yeast Schizosaccharomyces pombe dyn amin-related protein, which is essential for the maintenance of mitochondri al DNA, The Msp1p sequence displays typical features of a mitochondrial pro tein. Here we report in vitro and in vivo data that validate that predictio n. We demonstrate that the targeting sequence of Msp1p is processed by reco mbinant mitochondrial processing peptidase and that Msp1p is imported into S, pombe mitochondria in vitro in the presence of cellular extracts. We sho w that the first 109 residues of Msp1p encompass a functional peptide signa l that is sufficient to direct chimera to mitochondria. Immunofluorescence studies indicate that Msp1p staining colocalises with a mitochondrial marke r ana electron microscopy shows that the protein is located inside the mito chondria. Mitochondrial enrichment and fractionation further confirm that l ocalisation and show that Msp1p is anchored to the matrix side of the mitoc hondrial inner membrane. Finally, we report that overexpression of the Msp1 protein results in gross alteration of the mitochondrial structure and fun ction. All together our results suggest that Msp1p is an essential componen t for mitochondrial maintenance.