A ROLE FOR A EUKARYOTIC GRPE-RELATED PROTEIN, MGE1P, IN PROTEIN TRANSLOCATION

The 70-kDa heat shock proteins (hsp70s) function as molecular chaperon es in a wide variety of cellular processes through cycles of binding a nd release from substrate proteins coupled to cycles of ATP hydrolysis . In the prokaryote Escherichia coil, the hsp70 DnaK functions with tw o other proteins, DnaJ and GrpE, which modulate the activity of DnaK. While numerous hsp70s and DnaJ-related proteins have been identified i n eukaryotes, to our knowledge no GrpE-related proteins have been repo rted. We report the isolation and characterization of a eukaryotic grp E-related gene, MGE1. MGE1, an essential nuclear gene of the yeast Sac charomyces cerevisiae, encodes a soluble protein of the mitochondrial matrix. Cells with reduced expression of Mge1p accumulate the precurso r form of a mitochondrial protein. Since mitochondrial hsp70 is requir ed for translocation of precursors of mitochondrial proteins from the cytosol into the matrix of mitochondria, these data suggest that Mge1p acts in concert with mitochondrial hsp70 in protein translocation.