Channel-forming protein essential for import of protein precursors into mitochondria. Forms part of the preprotein translocase complex of the outer mitochondrial membrane (TOM complex). Interacts with mitochondrial targeting sequences (By similarity). Ubiquitously expressed. In the male germ line expression is detected early in premeiotic spermatogonia and is persistent to the end of meiosis. Expressed both maternally and zygotically. Belongs to the Tom40 family.