Intramitochondrial protein sorting. Isolation and characterization of the yeast MSP1 gene which belongs to a novel family of putative ATPases.

Replacement of the presequence of yeast cytochrome c1 by the amino-terminal 61 residues of MAS70, a yeast mitochondrial outer membrane protein, resulted in exclusive localization of the fusion protein (termed the 61-mC1 protein) to the outer membrane. When a cytochrome c1-deficient yeast strain was transformed with a plasmid encoding the fusion protein, the cells could not grow on nonfermentable carbon sources such as glycerol. We isolated a novel yeast gene MSP1 (mitochondrial sorting of proteins) whose overexpression causes mislocalization of the 61mC1 fusion protein to the inner membrane, probably via the intermembrane space, and thereby allows the host cells to grow on glycerol. The predicted MSP1 protein (MSP1) is a hydrophilic 40-kDa polypeptide containing a putative membrane-spanning domain near the amino terminus. Further sequence analyses revealed that MSP1 is a member of a novel family of putative ATPases which share a highly conserved domain of about 185 amino acid residues, including a consensus motif for a nucleotide binding site. MSP1 was found to be an intrinsic mitochondrial outer membrane protein of an apparent molecular mass of 40 kDa with a large domain facing to the cytosol. The MSP1 gene is not essential for the cell growth either on fermentable or nonfermentable carbon sources.