Schematic presentation of the integrated provirus of KoRV, structure of the envelope protein and sequence of the immunosuppressive domain. a, LTR, long terminal repeat; gag, group-specific antigen; pro-pol, protease-polymerase; env, envelope protein, FP, fusion peptide; isu, immunosuppressive domain; MSD, membrane spanning domain; CC, cysteine-cysteine loop. The arrow indicated the cleavage site between the surface (gp70) and the transmembrane (p15E) envelope protein. b, comparison of the sequence of the immunosuppressive domain of three KoRV subtypes and HIV-1. Identical amino acids are in orange, conservative exchanges in lilac.