MFT52, AN ACID-BRISTLE PROTEIN IN THE CYTOSOL THAT DELIVERS PRECURSORPROTEINS TO YEAST MITOCHONDRIA

We have identified a novel protein, Mft52, in the cytosol of yeast cel ls, Mft52 has a two-domain structure that includes a receptor-like car boxyl-terminal ''acid-bristle'' domain, which binds basic, amphipathic mitochondrial targeting sequences, Native Mft52, purified from the cy tosol of yeast cells, is found as a large particle eluting in the void volume of a Superose 6 gel filtration column, Fusion proteins, consis ting of mitochondrial targeting sequences fused to nonmitochondrial pa ssenger proteins, are targeted to mitochondria in wild type yeast cell s, but defects in the gene encoding Mft52 drastically reduce the deliv ery of these proteins to the mitochondria, We propose that Mft52 is a subunit of a particle that is part of a system of targeting factors an d molecular chaperones mediating the earliest stages of protein target ing to the mitochondria.