HUMAN ENDOGENOUS RETROVIRAL ELEMENT K10 (HERV-K10) ENCODES A FULL-LENGTH GAG HOMOLOGOUS 73-KDA PROTEIN AND A FUNCTIONAL PROTEASE

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 thr ee donors provided evidence that HERV-K10 genes contain an open readin g frame of 1966 bp spanning the entire gag-homologous region. In the p rokaryotic system the entire reading frame of the HERV-K10 gag gene co uld be expressed as a fusion protein exhibiting a molecular weight of about 110,000. In addition, when the gag-homologous region and the adj acent HERV-K10 protease gene were prokaryotically expressed, we observ ed a Gag-protease fusion protein that exhibited specific autoproteolyt ic activities and processing of HERV-K10 Gag protein. By introducing d eletions on the right end of the putative protease gene an autocatalyt ic site could be localized within 300 bp of the putative HERV-K10 prot ease gene. For the first time, these results provide evidence that the HERV-K10 encodes a full-length Gag protein and a functional protease.