Preproteins destined for mitochondria either are synthesized with amino-terminal signal
sequences, termed presequences, or possess internal targeting information within the
protein. The preprotein translocase of the outer mitochondrial membrane (designated Tom)
contains specific import receptors. The cytosolic domains of three import receptors, Tom20,
Tom22, and Tom70, have been shown to interact with preproteins. Little is known about the
internal targeting information in preproteins and the distribution of binding sequences for the …