Protein sorting to mitochondria

According to the endosymbiont hypothesis, mitochondria have lost
the autonomy of their prokaryotic ancestors. They have to import
most of their proteins from the cytosol because the mitochondrial
genome codes for only a small percentage of the polypeptides that
reside in the organelle. Recent findings show that the sorting of
proteins into the mitochondrial subcompartments and their folding
and assembly follow principles already developed in prokaryotes.
The components involved may have structural and functional
equivalents in bacteria.