ERV3, A Full-Length Human Endogenous Provirus: Sequence Analysis and Evolutionary Relationships

Abstract

The question of whether or not the human genome contains retroviral sequences is interesting in terms of both evolution and potential expression of these sequences. We have isolated baboon endogenous virus (BaEV) related sequences from a human DNA library (1) in order to address these questions (2,3). Hybridization and DNA sequence analyses of clones containing the human locus, ERV3, reveals that this region contains an apparent full length integrated retroviral genome (3,4). Significant homology was found between the gag and pol DNA sequences of this provirus and those of other mammalian type C retroviruses including: BaEV (5), Moloney murine murine leukemia virus (M-MuLV) (6), human T-cell leukemia virus (HTLV) (7) and two previously characterized human proviruses, ERV1 (2) and 51–1 (8). The complete nucleotide sequence has been obtained for both ERV3 long terminal repeats (LTRs). These elements contain known transcriptional control sequences within the LTRs in positions characteristic of mammalian type C retro-viruses. In contrast, the nucleotide sequence immediately following the U5 region of the 5’ LTR (that region commonly containing the primer binding site) is complementary not to the tRNApro utilized in the replication of type C mammalian retroviruses (9), but to a tRNAarg (10). This difference may define a new group of human retroviruses.