Multiple human endogenous retrovirus (HERV-K) loci with gag open reading frames in the human genome

Human endogenous retrovirus HERV-K is present in 25-30 copies per haploid human genome. At least one of these loci is capable of producing full-length Gag protein, high amounts of which have been detected in germ cell tumors and derived cell lines. The latter display HERV-K Gag-encoded retroviral particles. Here, we employed the protein truncation test (PTT) in combination with a monochromosomal hybrid mapping panel to identify the human chromosomes harboring HERV-K gag genes with an open reading frame for Gag protein. Eight human chromosomes were found to contain intact HERV-K gag genes. PTT results were corroborated by partial sequencing of subregions from different HERV-K gag genes. The high number of HERV-K Gag open reading frames supports the idea of retroviral sequences retaining a biological benefit in the human genome.