Chloroplast precursor protein translocon

Chloroplasts are believed to have originated from a photosynthetic, prokary otic ancestor. As the result of endosymbiotic evolution, most of the genes of the endocytobiont were displaced to the host nucleus. Today's chloroplas ts must import most of their proteins from the cytosol as precursors, Oligo meric protein complexes in the chloroplast outer and inner envelope membran es are responsible for the specific recognition and membrane translocation of precursor proteins. The translocon at the outer membrane of chloroplasts and the inner membrane of chloroplasts act jointly during the import proce ss. Several translocon subunits have been partially characterized in their molecular structure and function. Initial evidence indicates the prokaryoti c origin of some chloroplast translocon components. (C) 1999 Federation of European Biochemical Societies.