OXA1P, AN ESSENTIAL COMPONENT OF THE N-TAIL PROTEIN EXPORT MACHINERY IN MITOCHONDRIA

A number of nuclear encoded inner membrane proteins of mitochondria sp an the membrane in such a manner that their N termini are located in t he intermembrane space. Many of these proteins attain this membrane or ientation by undergoing an export step from matrix across the inner me mbrane. This export process, which resembles bacterial N-tail export f rom energetic and topogenic signal requirements, is facilitated by Oxa 1p, and protein that has homologues throughout prokaryotes and eukaryo tes. Oxa1p, as we have previously shown, is required to export the N a nd C termini of the mitochondrially encoded pCoxII to the intermembran e space. We demonstrate here that imported nuclear encoded proteins ph ysically interact with Oxa1p and depend on Oxa1p for efficient export of their N termini to the intermembrane space. Furthermore, Oxa1p inte racts with nascent polypeptide chains synthesized in mitochondria, inc luding the fully synthesized pCoxII and CoxIII species. Thus, Oxa1p re presents a component of a general export machinery of the mitochondria l inner membrane.