Insertional polymorphisms of full-length endogenous retroviruses in humans

Human endogenous retrovirus K (HERV-K) is distinctive among the retroviruse s in the human genome in that many HERV-K proviruses were inserted into the human germline after the human and chimpanzee lineages evolutionarily dive rged [1, 2]. However, all full-length endogenous retroviruses described to date in humans are sufficiently old that all humans examined were homozygou s for their presence [1]. Moreover, none are intact; all have lethal mutati ons [1, 3, 4]. Here, we describe the first endogenous retroviruses; in huma ns for which both the full-length provirus and the preintegration site alle les are shown to be present in the human population today. One provirus, ca lled HERV-K113, was present in about 30% of tested individuals, while a sec ond, called HERV-K115, was found in about 15%. HERV-K113 has full-length op en reading frames (ORFs) for all viral proteins and lacks any nonsynomymous substitutions in amino acid motifs that are well conserved among retroviru ses. This is the first such endogenous retrovirus identified in humans. The se findings indicate that HERV-K remained capable of reinfecting humans thr ough very recent evolutionary times and that HERV-K113 is an excellent cand idate for an endogenous retrovirus that is capable of reinfecting humans to day.