IMPORT OF CARRIER PROTEINS INTO THE MITOCHONDRIAL INNER MEMBRANE MEDIATED BY TIM22

TRANSLOCATION of mitochondrial preproteins across the inner membrane i s facilitated by the TIM machinery(1-8). Tim34 binds to matrix targeti ng signals and initiates membrane potential-dependent import(8). Tim23 and Tim17 are constituents of a translocation channel across the inne r membrane(6). Tim44 is associated with this channel at the matrix sid e(6), and Tim44 recruits mitochondrial Hsp70 and its co-chaperone Mge1 , which drive protein translocation into the matrix using ATP as an en ergy source(9-14). Tim22 is a new component of the import machinery of mitochondria, which shares sequence similarity with both Tim23 and Ti m17. Here we report that Tim22 is required for the import of proteins of the mitochondrial ADP/ATP carrier (AAC) family into the inner membr ane. Members of the yeast AAC family are synthesized without matrix ta rgeting signals(15,16). Tim22 is in an assembly of high relative molec ular mass that is distinct from the Tim23-Tim17 complex(6). Import of proteins of the AAC family is independent of Tim23, and import of matr ix targeting signals containing preproteins is independent of Tim22.