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. Expressed in lung, placenta, testis, peripheral blood lymphocytes, and teratocarcinoma cell lines. Has a type 1 genome. The HERV-K(HML-2) family contains type 1 and type 2 genomes depending on the absence or presence of 292 nucleotides at the 5'-end of the env gene resulting in Env proteins of distinct sizes. Despite their overall retroviral envelope structure HERV-K(HML-2) type 1 envelope proteins lack a predictable signal sequence. Subgenomic RNA transcripts coding for full-length envelope proteins have been detected for both type of genomes. Intergenic, closest flanking genes being RPL24 and FLJ23047. Belongs to the beta type-B retroviral envelope protein family. HERV class-II K(HML-2) env subfamily. No predictable signal peptide. Truncated; premature stop codon in the surface protein.