Hydrophobicity profiles and phylogenetic analysis of Env proteins of BERV-K1 and -K2. (A) Hydrophobicity profiles of BERV-K1 and -K2 Env proteins. Gray shading indicates the fusion peptide and the transmembrane domain. (B) Phylogenetic analyses of the BERV-K1 and -K2 env genes. The phylogenetic tree of the entire TM-encoding region of env was constructed by the neighbor-joining method. enJSRV, endogenous Jaagsiekte sheep retrovirus; enMMTV, endogenous mouse mammary tumor virus; HERV-K, human endogenous retrovirus type K; ALV, avian leukemia virus; FIV, feline immunodeficiency virus; HIV-1, human immunodeficiency virus type 1; MuLV, murine leukemia virus; FeLV-B, feline leukemia virus subgroup B; HTLV-1, human T-cell leukemia virus type 1; BLV, bovine leukemia virus.