The structure of precursor proteins during import into mitochondria

Precursor proteins must be at least partially unfolded during import into m itochondria, but their actual conformation during translocation is not know n. Are proteins fully unfolded and threaded through the import machinery am ino acid by amino acid, or do they retain some partial structure? The foldi ng pathway of most proteins in vitro contains a partially folded intermedia te known as the molten globule state, and it has been suggested that protei ns are in the molten globule state during translocation across membranes. H ere we show that precursors are normally fully unfolded during import into mitochondria, However, precursors containing residual structure can be impo rted, if less efficiently,