CYTOSOLIC FACTORS IN MITOCHONDRIAL PROTEIN IMPORT

In vitro import studies have confirmed the participation of cytosolic protein factors in the import of various precursor proteins into mitoc hondria. The requirement for extramitochondrial adenosine triphosphate for the import of a group of precursor proteins seems to be correlate d with the chaperone activity of the cytosolic protein factors. One of the cytosolic protein factors is hsp70, which generally recognizes an d binds unfolded proteins in the cytoplasm. Hsp70 keeps the newly synt hesized mitochondrial precursor proteins in import-competent unfolded conformations. Another cytosolic protein factor that has been characte rized is mitochondrial import stimulation factor (MSF), which seems to be specific to mitochondrial precursor proteins. MSF recognizes the m itochondrial precursor proteins, forms a complex with them and targets them to the receptors on the outer surface of mitochondria.