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. Author manuscript; available in PMC: 2016 Jul 18.
Published in final edited form as: Clin Sci (Lond). 2016 Mar;130(6):393–407. doi: 10.1042/CS20150707

Figure 2. Synthesis and assembly of COX subunits.

Figure 2

A scheme summarizing what is presently known about the pathways for the integrated synthesis and assembly of COX subunits expressed from the nuclear and mitochondrial genomes. Protein subunits translated on cytosolic ribosomes with N-terminal presequences are first transported by the outer membrane TOM complex and are subsequently matured and sorted by the TIM and MITRAC machineries to the intermembrane space, inner membrane, or matrix where they interact with partner proteins to form assembly intermediates (144–146). Subunits encoded by mtDNA genes are translated on mitochondrial ribosomes attached to the matrix side of the inner membrane. Following insertion into the inner membrane by Oxa1 they interact with their nucleo-cytoplasmic partners to form subcomplexes that subsequently assemble into COX. The overall process is assisted by numerous proteins acting in transport, translation, chaperoning of different assembly steps. Oxa1 is also involved in the biogenesis of other respiratory chain complexes. Some of the genes coding for ancillary factors (indicated in red) have been found to be mutated in COX deficient patients. IM, inner membrane; OM, outer membrane; 1, 2, 4, 5a, COX subunits (purple)