Mechanisms of mitochondrial protein import.

1. Most proteins of cell organelles are synthesized as precursor proteins on cytosolic polysomes and are directed by signal sequences into the correct compartments. 2. In this review, the characteristics of mitochondrial protein uptake will be described, including the specific recognition, membrane translocation, proteolytic processing and folding of nuclear-encoded precursor proteins. 3. Recent studies indicate that a proteinaceous machinery located in the mitochondrial membranes and matrix performs these key steps of protein import.