Nuclear integrations of mitochondrial DNA in primates: Inference of associated mutational events

To infer the possible mutational events taking place along the interorganel lar transfer of genetic material from mitochondria to the nucleus, four int egrations of mitochondrial DNA (mtDNA) in the human genome were characteriz ed together with their flanking nuclear sequences. By determining their pre sence/absence status in different primate species, these integrations were inferred to have occurred on the lineages leading to catarrhines (Old World monkeys and hominoids), to hominoids and to humans, respectively. in case of a polymorphic state, with;respect to its presence in a certain species, each preintegration sequence was either cloned in the same species or in a primate taxon that branched off before the transfer of the mtDNA to the nuc leus took place. For the four mtDNA integrations presented here, random mob ilization of the mtDNA and differing mechanisms for generating free ends in the nuclear target sequences can be inferred. Additionally, no common sequ ence features at the preintegration sites could be observed for these integ rations. Moreover, the comparisons of the sites before and after integratio n suggest different ways of integration. Thus, mtDNA integrations represent unique molecular recombinations in the evolutionary history and can, accor ding to their presence/absence status in different species, help to determi ne the branching order in phylogenetic trees.