Mitochondrial DNA repair pathways.

It has long been held that there is no DNA repair in mitochondria. Early observations suggested that the reason for the observed accumulation of DNA damage in mitochondrial DNA is that DNA lesions are not removed. This is in contrast to the very efficient repair that is seen in the nuclear DNA. Mitochondrial DNA does not code for any DNA repair proteins, but it has been observed that a number of repair factors can be found in mitochondrial extracts. Most of these participate in the base excision DNA repair pathway which is responsible for the removal of simple lesions in DNA. Recent work has shown that there is efficient base excision repair in mammalian mitochondria and there are also indications of the presence of more complex repair processes. Thus, an active field of mitochondrial DNA repair is emerging. An understanding of the DNA repair processes in mammalian mitochondria is an important current challenge and it is likely to lead to clarification of the etiology of the common mutations and deletions that are found in mitochondria, and which are thought to cause various human disorders and to play a role in the aging phenotype.