Retroviral envelope proteins mediate receptor recognition and membrane fusion during early infection. Endogenous envelope proteins may have kept, lost or modified their original function during evolution. This endogenous envelope protein has lost its original fusogenic properties. A ribosomal frameshift due to a slippery site present at the end of the gene may lead to a longer protein. Low expression in skin and testis. The CKS-17 immunosuppressive domain is present in many retroviral envelope proteins. As a synthetic peptide, it inhibits immune function in vitro and in vivo (By similarity). The CXXC motif is highly conserved across a broad range of retroviral envelope proteins. It is thought to participate in the formation of a labile disulfide bond possibly with the CX6CC motif present in the transmembrane domain (By similarity). Orthologs in P.troglodytes (truncated), G.gorilla (truncated). Belongs to the gamma type-C retroviral envelope protein family. HERV class-I F(c)2 env subfamily. The cleavage site does not match the consensus. CKS-17 sequence does not match the minimal active consensus. No predictable signal peptide. Truncated; premature stop codon upstream of the potential transmembrane domain.