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. Author manuscript; available in PMC: 2014 Jul 16.
Published in final edited form as: Cell. 2009 Aug 21;138(4):628–644. doi: 10.1016/j.cell.2009.08.005

Figure 1. Principles of Mitochondrial Protein Biogenesis.

Figure 1

(A) Cytosolic and mitochondrial protein synthesis. Most mitochondrial proteins are synthesized on cytosolic ribosomes and are imported into the organelle. About 1% of mitochondrial proteins are synthesized inside the organelle.

(B) Sorting pathways of mitochondria. The translocase of the outer membrane (TOM complex) is the main entry gate into mitochondria. Subsequently, the precursor proteins follow different sorting pathways. MIA, mitochondrial intermembrane space assembly; OXA, insertase/export machinery of the inner membrane; SAM, sorting and assembly machinery; TIM22 complex, carrier translocase of the inner membrane; TIM23 complex, presequence translocase of the inner membrane. (Inset) The TOM complex consists of seven different subunits. The receptors Tom20, Tom22, and Tom70 recognize precursor proteins and transfer them to the central component, the channel-forming Tom40. Three small Tom proteins, Tom5, Tom6, and Tom7, are involved in the assembly and dynamics of the TOM complex. (Presequence-carrying precursor proteins, red; hydrophobic precursors with internal targeting signals, blue.)