MEMBRANE TRANSLOCATION OF MITOCHONDRIALLY CODED COX2P - DISTINCT REQUIREMENTS FOR EXPORT OF N-TERMINI AND C-TERMINI AND DEPENDENCE ON THE CONSERVED PROTEIN-OXA1P

To study in vivo the export of mitochondrially synthesized protein fro m the matrix to the intermembrane space, we have fused a synthetic mit ochondrial gene, AXG8''', to the Saccharomyces cerevisiae COX2 gene in mitochondrial DNA. The Arg8(m)p moiety was translocated through the i nner membrane when fused to the Cox2p C terminus by a mechanism depend ent on topogenic information at least partially contained within the e xported Cox2p C-terminal tail. The pre-Cox2p leader peptide did not si gnal translocation. Export of the Cox2p C-terminal tail, but not the N -terminal tail, was dependent on the inner membrane potential. The mit ochondrial export system does not closely resemble the bacterial Sec t ranslocase. However, normal translocation of both exported domains of Cox2p was defective in cells lacking the widely conserved inner membra ne protein Oxa1p.