Many different human endogenous retrovirus (HERV) families are expressed in normal placental tissue at high levels, suggesting that HERVs are functionally important in reproduction. This gene is part of a human endogenous retrovirus provirus on chromosome 6 that has inactivating mutations in the gag and pol genes. This gene is the envelope glycoprotein gene which appears to have been selectively preserved. The gene's protein product plays a major role in placental development and trophoblast fusion. The protein has the characteristics of a typical retroviral envelope protein, including a cleavage site that separates the surface (SU) and transmembrane (TM) proteins which form a heterodimer.