A MITOCHONDRIAL PROTEASE WITH 2 CATALYTIC SUBUNITS OF NONOVERLAPPING SPECIFICITIES

The mitochondrial inner membrane protease is required for the maturati on of mitochondrial proteins that are delivered to the intermembrane s pace. In the yeast Saccharomyces cerevisiae, this protease is now show n to be a complex that contains two catalytic subunits, Imp2p and the previously identified Imp1p. Primary structure similarity indicates th at Imp1p and Imp2p are related to each other and to the family of euba cterial and eukaryotic signal peptidases. Imp1p and Imp2p have separat e, nonoverlapping substrate specificities. In addition to its catalyzi ng the cleavage of intermembrane space sorting signals, Imp2p is requi red for the stable and functional expression of Imp1p. Thus, inner mem brane protease, and by analogy eukaryotic multisubunit signal peptidas es, may have acquired multiple catalytic subunits by gene duplication to broaden their range of substrate specificity.