IDENTIFICATION OF MIM23, A PUTATIVE COMPONENT OF THE PROTEIN IMPORT MACHINERY OF THE MITOCHONDRIAL INNER MEMBRANE

A screening for yeast mutants impaired in mitochondrial protein import led to the identification of two genes (MPI1 and MPI2) encoding the e ssential components MIM44 and MIM17 of the inner membrane import machi nery. We analyzed twelve additional mutants obtained in the screening and found two further complementation groups. One group represents mut ants of SSC1, the gene encoding mitochondrial hsp70, an essential matr ix protein required for protein import across the inner membrane. The second complementation group represents mutants of a new gene (MPI3) e ncoding a 23 kDa integral inner membrane protein (MIM23). MIM23 is syn thesized without a presequence, and its import to the inner membrane r equires a membrane potential. MIM23 contains a domain homologous to ha lf of MIM17. We speculate that MIM23 is a new member of the protein im port machinery of the mitochondrial inner membrane.