ACIDIC RECEPTOR DOMAINS ON BOTH SIDES OF THE OUTER-MEMBRANE MEDIATE TRANSLOCATION OF PRECURSOR PROTEINS INTO YEAST MITOCHONDRIA

Mitochondrial precursor proteins made in the cytosol bind to a hetero- oligomeric protein import receptor on the mitochondrial surface and th en pass through the translocation channel across the outer membrane, T his translocation step is accelerated by an acidic domain of the recep tor subunit Mas22p, which protrudes into the intermembrane space, This 'trans' domain of Mas22p specifically binds functional mitochondrial targeting peptides with a K-d Of <1 mu M and is required to anchor the N-terminal targeting sequence of a translocation-arrested precursor i n the intermembrane space, If this Mas22p domain is deleted, respirati on-driven growth of the cells is compromised and import of different p recursors into isolated mitochondria is inhibited 3- to 8-fold, Bindin g of precursors to the mitochondrial surface appears to be mediated by cytosolically exposed acidic domains of the receptor subunits Mas20p and Mas22p, Translocation of a precursor across the outer membrane thu s appears to involve sequential binding of the precursor's basic and a mphiphilic targeting signal to acidic receptor domains on both sides o f the membrane.