Chimeric mitochondrial minichromosomes of the human body louse, Pediculus humanus: Evidence for homologous and non-homologous recombination

The mitochondrial (mt) genome of the human body louse, Pediculus humanus, consists of 18 minichromo-
somes. Each minichromosome is 3 to 4 kb long and has 1 to 3 genes. There is unequivocal evidence for
recombination between different mt minichromosomes in P. humanus. It is not known, however, how these
minichromosomes recombine. Here, we report the discovery of eight chimeric mt minichromosomes in P.
humanus. We classify these chimeric mt minichromosomes into two groups: Group I and Group II. Group I
chimeric minichromosomes contain parts of two different protein-coding genes that are from different
minichromosomes. The two parts of protein-coding genes in each Group I chimeric minichromosome are
joined at a microhomologous nucleotide sequence; microhomologous nucleotide sequences are hallmarks of
non-homologous recombination. Group II chimeric minichromosomes contain all of the genes and the non-
coding regions of two different minichromosomes. The conserved sequence blocks in the non-coding regions
of Group II chimeric minichromosomes resemble the “recombination repeats” in the non-coding regions of
the mt genomes of higher plants. These repeats are essential to homologous recombination in higher plants.
Our analyses of the nucleotide sequences of chimeric mt minichromosomes indicate both homologous and
non-homologous recombination between minichromosomes in the mitochondria of the human body louse.

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