Substrate recognition and binding subunit of the essential mitochondrial processing protease (MPP), which cleaves the mitochondrial sequence off newly imported precursors proteins. Heterodimer of mppa-1 (alpha) and mppb-1 (beta) subunits, forming the mitochondrial processing protease (MPP) in which mppa-1 is involved in substrate recognition and binding and mppb-1 is the catalytic subunit. RNAi-mediated knockdown causes 63 percent embryonic lethality (PubMed:16788047). Embryonic lethality is further increased in simultaneous RNAi-mediated knockdown of mppa-1 and mppb-1 or ucr-1 and mppa-1 (PubMed:16788047). Belongs to the peptidase M16 family. Although it belongs to the peptidase M16 family, lacks the zinc-binding sites and appears to lack catalytic activity in vitro.