MOM22 IS A RECEPTOR FOR MITOCHONDRIAL TARGETING SEQUENCES AND COOPERATES WITH MOM19

Recognition of targeting signals is a crucial step in protein sorting within the cell, So far, only a few components capable of deciphering targeting signals have been identified, and insights into the chemical nature of the interaction between the signals and their receptors are scarce, Using highly purified mitochondrial outer membrane vesicles, we demonstrate that MOM22 and MOM19, components of the protein import complex of the outer membrane, bind preproteins at the mitochondrial s urface in a reversible fashion, Interaction specifically and directly occurs with the N-terminal presequence and is abolished after inactiva tion of either MOM22 or MOM19, Binding is salt sensitive, suggesting t hat recognition involves electrostatic forces between the positive cha rges of the presequence and the acidic cytosolic domain of MOM22, MOM1 9 and MOM22 can be cross-linked with high efficiency, We propose that the two proteins form a complex which functions as the presequence rec eptor at the mitochondrial surface and facilitates the movement of pre proteins into the translocation pore.