Dissociation of import of the Rieske iron-sulfur protein into Saccharomyces cerevisiae mitochondria from proteolytic processing of the presequence.

The correlation between the import of the Rieske iron-sulfur protein into the mitochondrial matrix and processing of the precursor protein by matrix processing peptidase was investigated using high concentrations of metal chelators and iron-sulfur protein in which the recognition site for the matrix processing peptidase was destroyed by site-directed mutagenesis. High concentrations of EDTA and o-phenanthroline inhibit import of iron-sulfur protein into the matrix. The non-chelating structural isomers m-phenanthroline and p-phenanthroline inhibit import similar to o-phenanthroline, indicating that inhibition of import is mainly independent of the metal chelating ability of the compounds. Iron-sulfur protein in which the recognition site for the matrix processing peptidase had been destroyed by a point mutation was efficiently imported into the matrix space. Import of this mutant iron-sulfur protein was inhibited by the same concentrations of EDTA and o-phenanthroline which inhibit import of the wild-type protein. These results indicate that import of the iron-sulfur protein into the mitochondrial matrix is independent of proteolytic processing of the presequence, and that o-phenanthroline together with EDTA inhibits import of iron-sulfur protein into the matrix space of mitochondria by inhibiting a step other than proteolysis of the presequence.