RECOGNITION OF MITOCHONDRIA-TARGETING SIGNALS BY A CYTOSOLIC IMPORT STIMULATION FACTOR, MSF

MSF, a mitochondrial import stimulation factor purified from rat liver cytosol, is an ATP-dependent precursor protein conformational modulat or. As a step toward understanding the specificity of substrate recogn ition by MSF, various synthetic peptides were examined for their abili ty to induce MSF ATPase activity. The peptides corresponding to variou s mitochondria-targeting signal sequences elicited significant ATPase activity. MSF bound the synthetic mitochondrial signal peptides, and A TP hydrolysis caused dissociation of the peptides from MSF. Basic amin o acid residues in the signal peptides seemed to be essential for reco gnition. Thus, MSF is a member of the polypeptide chain-binding protei n family with unique recognition specificity and is distinct from the hsp70 family of proteins.