Identification of Mutations in mtDNA from Patients Suffering Mitochondrial Diseases
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The human mitochondrial genome (
see
Fig. 1 ) is a 16,569-bp (base pair) circle of double-stranded DNA (
1
). It contains genes encoding 2 ribosomal RNAs, 22 transfer RNAs, and 13 structural genes, all of which are subunits of the respiratory chain complexes. Of the 13 structural genes, 7 encode subunits of complex I (NADH-CoQ oxidoreductase), 1 encodes the cytochrome-b subunit of complex III (CoQ-cytochrome-c oxidoreductase), 3 encode subunits of complex IV (cytochrome-c oxidase, or COX), and 2 encode subunits of complex V (ATP synthase). Each of these complexes also contains subunits encoded by nuclear genes, which are imported from the cytoplasm and assembled, together with the mtDNA-encoded subunits, into the respective holoenzymes, which are embedded in the mitochondrial inner membrane. Complex II (succinate dehydrogenase-CoQ oxidoreductase), of which succinate dehydrogenase (SDH) is a component, is encoded entirely by nuclear genes.
Fig. 1.
The human mitochondrial genome. The structural genes for the mtDNA-encoded 12S and 16S ribosomal RNAs, the subunits of NADH-coenzyme Q oxidoreductase (ND), cytochrome-c oxidase (COX), cytochrome-b (Cyt b), and ATP synthase (A), and 22 tRNAs, are shown, as are the origins of heavy- (O
H
) and light (O
L
) -strand replication.
