Human Endogenous Retroviral Element K10 (HERV-K10) Encodes a Full-Length Gag Homologous 73-kDa Protein and a Functional Protease

Abstract

The gag-homologous region of the human endogenous retrovirus K10 (HERV-K10) was amplified by PCR from human genomic DNA and was analyzed by DNA cloning, sequencing, and expression of open reading frames in the prokaryotic pATH expression system. The analysis of genomic DNA of three donors provided evidence that HERV-K10 genes contain an open reading frame of 1966 bp spanning the entire gag-homologous region. In the prokaryotic system the entire reading frame of the HERV-K10 gag gene could be expressed as a fusion protein exhibiting a molecular weight of about 110,000. In addition, when the gag-homologous region and the adjacent HERV-K10 protease gene were prokaryotically expressed, we observed a Gag-protease fusion protein that exhibited specific autoproteolytic activities and processing of HERV-K10 Gag protein. By introducing deletions on the right end of the putative protease gene an autocatalytic site could be localized within 300 bp of the putative HERV-K10 protease gene. For the first time, these results provide evidence that the HERV-K10 encodes a full-length Gag protein and a functional protease.

Inhibition of Human Endogenous Retrovirus-K10 Protease in Cell-free and Cell-based Assays

“…The existence of a functional HERV-K protease was inferred from the presence of processed Gag proteins in teratocarcinoma cells (5). Direct evidence for a functional protease activity came from expression of different clones in E. coli (15,17,25,38).…”

“…Typically the coding regions of HERV-K elements are far less disrupted by mutations than other HERV families, and protein synthesis has been observed for all the main retroviral genes. The HERV-K Gag precursors are cleaved into major core, matrix, and nucleocapsid components (14 -16), presumably by HERV-K protease, because functional activity has been demonstrated for this enzyme (15,17).…”

Human endogenous retrovirus protein cORF supports cell transformation and associates with the promyelocytic leukemia zinc finger protein

“…For polyclonal antisera, rabbits were immunized with cORF protein as described (Mueller-Lantzsch et al, 1993). For monoclonal antibodies, cORF-protein was injected into Lou/c rats and antibodies were generated as described previously .…”

Characterization of the human endogenous retrovirus K proteinase

“…The human endogenous retrovirus K (HERV-K) family has been found to include members with open reading frames (ORFs) representing gag, prt, pol and env (Ono et al, 1986;Mueller-Lantzsch et al, 1993;L6wer et aI., 1993). Recently we were able to demonstrate a correlation between the expression of HERV-K gag sequences and seminomas in humans (Sauter et al, 1995).…”

“…Expression ofpT7-pro0.7 in E. coli BL21DE3 resulted in the autocatalytic cleavage of the pT7-pro0. (Ono et al, 1986;Mueller-Lantzsch et al, 1993;L6wer et al, 1993). All constructs except pT7-pro0.7 and pSPTgag-prot were expressed as TrpE fusion proteins in E. coli.…”