CHARACTERIZATION OF THE HUMAN ENDOGENOUS RETROVIRUS-K PROTEINASE

The proteinase of the human endogenous retrovirus K (HERV-K) shows sim ilarity to retrovirus aspartic proteinases. It is translated from a tr anscript composed of gag and prt. The proteinase was expressed either as full-length native protein or as truncated protein in Escherichia c oli. Functional protein was demonstrated by its autocatalytic cleavage into an 18 kDa fragment recognized by a polyclonal antiserum. This au tocatalytic cleavage was specifically inhibited by a human immunodefic iency virus type 1 proteinase inhibitor. The HERV-K proteinase express ed in E. coli was capable of cleaving HERV-K Gag translated in vitro. Major protein fragments of 39 and 30 kDa, and minor protein fragments of 26, 22 and 21 kDa were obtained. Similar fragments are also observe d in the human teratocarcinoma cell line Teral. Our data suggest that the HERV-K proteinase is functionally equivalent to other retrovirus p roteinases and thus probably functions in the processing of Gag precur sor protein.