Human endogenous retrovirus HERV-K(HML-2) proviruses with Rec protein coding capacity and transcriptional activity

The human endogenous retrovirus family HERV-K(HML-2) encodes the so-called Rec protein that displays functional similarities to the HIV(REV) protein. The number of proviruses producing Rec protein was hitherto unknown. We therefore analyzed the human genome sequence data and determined seven HERV-K(HML-2) proviruses potentially capable of producing Rec both on the mRNA and the protein level. We analyzed Rec mRNA expression in the Tera-1 cell line and in synovial tissue, and in the expressed sequence tag (EST) database. Diagnostic nucleotides assigned transcriptionally active and Rec-encoding proviruses to human chromosomes 6, 7, 11, and 12. Differently spliced mRNAs were also identified. The various active proviruses encode almost identical Rec proteins. Our study contributes to the understanding of the biology of HERV-K(HML-2) Rec protein. Our study further demonstrates that minor sequence differences among proviruses allow assigning HERV transcripts to particular proviral loci. Extended studies will eventually yield a more complete image of HERV transcription, regulation, and biological significance in diverse human tissues.