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Sequences homologous to human herpesvirus 6 (HHV-6) are integrated within the nuclear genome of about 1% of humans, but it is not clear how this came about. It is also uncertain whether integrated HHV-6 can reactive into an infectious virus. HHV-6 integrates into telomeres, and this has recently been associated with polymorphisms affecting MOV10L1. MOV10L1 is located on the subtelomere of chromosome 22q (chr22q) and is required to make PIWI-interacting RNAs (piRNAs). As piRNAs block germline integration of transposons, piRNA-mediated repression of HHV-6 integration has been proposed to explain this association. In vitro, recombination of the HHV-6 genome along its terminal direct repeats (DRs) leads to excision from the telomere and viral reactivation, but the expected "solo-DR scar" has not been described in vivo. Here we screened for integrated HHV-6 in 7,485 Japanese subjects using whole-genome sequencing (WGS). Integrated HHV-6 was associated with polymorphisms on chr22q. However, in contrast to prior work, we find that the reported MOV10L1 polymorphism is physically linked to an ancient endogenous HHV-6A variant integrated into the telomere of chr22q in East Asians. Unexpectedly, an HHV-6B variant has also endogenized in chr22q; two endogenous HHV-6 variants at this locus thus account for 72% of all integrated HHV-6 in Japan. We also report human genomes carrying only one portion of the HHV-6B genome, a solo-DR, supporting in vivo excision and possible viral reactivation. Together these results explain the recently-reported association between integrated HHV-6 and MOV10L1/piRNAs, suggest potential exaptation of HHV-6 in its coevolution with human chr22q, and clarify the evolution and risk of reactivation of the only intact (non-retro)viral genome known to be present in human germlines. Author summary: Human herpesvirus 6 (HHV-6) infects most people during childhood and can reactivate later in life to contribute to diseases. The HHV-6 genome is also inherited by about 1% of people, included in the end "cap" of one of their 46 chromosomes. Little is known about how HHV-6 genomes entered human genomes, whether or not they still do, and the risk this poses for virus reactivation. We looked for HHV-6 in genome sequences from ~7,500 Japanese people. Most integrated HHV-6 variants have been co-evolving with human chromosomes for many generations. Surprisingly, in almost three-fourths of Japanese people with HHV-6 in their genome, HHV-6 is integrated in the same end of the same chromosome– 22q. Persistence of the HHV-6 genome within the short "cap" that preserves the end of chromosome 22q raises the question of whether the integrated viral sequence has taken on a useful function for this chromosome. Some human genomes harbor only one part of the HHV-6 genome–the same part that remains after experimental HHV-6 reactivation, during which most of the virus is cut out of the genome. This suggests that integration of HHV-6 into inherited human genomes is not irreversible, and possibly leads to production of infectious virus. [ABSTRACT FROM AUTHOR]