MITOCHONDRIAL HSP70 MIM44 COMPLEX FACILITATES PROTEIN IMPORT/

Protein translocation into mitochondria requires the mitochondrial pro tein Hsp70. This molecular chaperone of the mitochondrial matrix is re cruited to the protein import machinery by MIM44, a component associat ed with the inner membrane of the mitochondria. Formation of the mt-Hs p70/MIM44 complex is regulated by ATP. MIM44 and mt-Hsp70 interact in a sequential manner with incoming segments of unfolded preproteins and thereby facilitate stepwise vectorial translocation of proteins acros s the mitochondrial membranes. The complex appears to act as a molecul ar ratchet which is energetically driven by the hydrolysis of ATP.