The residues from P4-P4 0 were collected for each substrate cleavage. Figure 1 shows the number of peptidases showing some selectivity for one or two residues in each binding pocket from S4 to S4 0 . Clearly, many peptidases have extended substrate-binding sites with preferences beyond S1, with 52 showing a preference in the S4 pocket. There are a few peptidases that have a preference at S5 (30), but a preference so far from the scissile bond is rare. It is conceivable that mitochondrial intermediate peptidase (M03.006), which removes a transit octapeptide from the N-terminus of proteins synthesized in the cytoplasm but destined for the mitochondrial matrix, may have a preference as far away from the cleavage site as S8 (31) . Preference on the prime side of the scissile bond is thought to rarely extend beyond the S1 0 pocket, but Figure 1 shows that 32 different peptidases have a preference in S4 0 .