Presence of env genes in members of the RTVL-H family of human endogenous retrovirus-like elements.

We have found that the RTVL-H family of human endogenous retrovirus-like elements was highly expressed in lung squamous cell carcinoma tissue and several human cell lines. We determined the nucleotide sequences of several cDNA clones and found a unique sequence that was not present in the published "prototypic" RTVL-H sequence. An open reading frame in this region encoded an amino acid sequence homologous to the conserved sequence in the transmembrane envelope protein of various retroviruses. Two genomic clones that encoded this sequence were obtained and sequenced. One RTVL-H element containing the env gene was 8.7 kilobase pairs in length. The putative env gene, consisting of about 1800 base pairs, had two open reading frames interrupted by a termination codon. The amino acid sequence of this region showed significant homology with those of other retroviral envelope proteins and contained eight potential glycosylation sites. There were estimated to be about 100 copies of RTVL-H elements containing the env gene per haploid human genome.