ATP-independent protease that degrades mitochondrial transit peptides after their cleavage both in intermembrane space and in matrix. Also degrades other unstructured peptides (By similarity). Binds 1 zinc ion per subunit. Homodimer. May also be present in the mitochondrial matrix. Present with 6140 molecules/cell in log phase SD medium. Belongs to the peptidase M16 family. PreP subfamily.