Figure 4.

Schematic diagram of the feline immunodeficiency virus (FIV) Env glycoprotein. (Top) The leader peptide and the surface (SU) and transmembrance (TM) subunits are shown. The three major regions that constitute the TM are indicated: ectodomain (red box), membrane-spanning domain (grey box) and the cytoplasmic tail (light-blue box). Amino acid numbering corresponds to the Env protein of the Petaluma isolate. (Bottom) Amino acid sequences of the membrane anchor and the cytoplasmic domain of FIV Env. The four highly conserved cysteines as well as the tyrosine-based endocytosis motif within the cytoplasmic tail are highlighted below the sequence.