Rare creation of recombinant mtDNA haplotypes in mammalian tissues.

The problem of whether recombinant mtDNAs are created in mammalian cells has been controversial for many years. We show convincing evidence for the very rare creation of recombinant mtDNA haplotypes by isolating human somatic hybrid cells and by generating mice carrying two different mtDNA haplotypes. To avoid misinterpretation of PCR-jumping products as recombinants, we used purified mtDNAs for cloning and sequencing. The results showed that only three of 318 clones of mtDNA purified from mouse tissues corresponded to recombinant mtDNA haplotypes, whereas no recombinants were found in human somatic hybrid cells. Such an extremely low frequency of mtDNA recombination does not require any revision of important concepts on human evolution that are based on its absence. Considering the high concentration of reactive oxygen species around the mtDNA and its frequent strand breakage, recombinant clones would correspond to gene conversion products created by repair of nucleotide mismatches.