Cytosol-synthesized preproteins destined for the mitochondria are transport
ed across the outer membrane by the translocase of the mitochondrial outer
membrane (TOM complex). This dynamic transport machinery can be divided int
o receptors that recognize preprotein targeting signals and components of t
he general import pore complex that mediate preprotein transport across the
outer membrane. This review focuses on recent studies dealing with the cen
tral questions regarding the pore-forming subunits, and architecture and ga
ting of the translocation channel of the outer membrane.