An almost-intact human endogenous retrovirus K on human chromosome 7

In contrast to the many defective endogenous retroviral sequences, the human endogenous retrovirus HERV-K(HML-2) (ref. 1) group shows conservation of intact retroviral genes (for review, see ref. 2). We have previously reported evidence that human chromosome 7 contains both intact HERV-K gag and env genes, indicating the possible existence of an HERV-K provirus with intact open reading frames (ORFs) for all retroviral genes. We screened a chromosome 7-specific cosmid library (LLNL single chromosome cosmid library LL07NC01) for clones containing both gag and env sequences and identified cosmid clone Y20-B19 as harbouring an HERV-K provirus. This provirus, which we called HERV-K(HML-2.HOM), contains ORFs for all the retroviral genes (Fig. 1a) and represents the most intact human endogenous retrovirus to date.