Evidence for genomic rearrangements mediated by human endogenous retroviruses during primate evolution

Human endogenous retroviruses (HERVs), which are remnants of past retrovira l infections of the germline cells of our ancestors(1), make up as much as 8% of the human genome and may even outnumber genes(2,3). Most HERVs seem t o have entered the genome between 10 and 50 million years ago, and they com prise over 200 distinct groups and subgroups(1,4). Although repeated sequen ce elements such as HERVs have the potential to lead to chromosomal rearran gement through homologous recombination between distant loci, evidence for the generality of this process is lacking. To gain insight into the expansi on of these elements in the genome during the course of primate evolution, we have identified 23 new members of the HERV-K (HML-2) group, which is tho ught to contain the most recently active members. Here we show, by phylogen etic and sequence analysis, that at least 16% of these elements have underg one apparent rearrangements that may have resulted in large-scale deletions , duplications and chromosome reshuffling during the evolution of the human genome.