FIG. 1.

(A) Schematic diagram of the feline immunodeficiency virus (FIV) Env glycoprotein showing the cleavage site between its surface (SU) and transmembrane (TM) subunits (arrow). The variable regions of the SU glycoprotein (V1–V6) are indicated with hatched boxes whereas the structural features of the TM glycoprotein: ectodomain, membrane-spanning domain, and cytoplasmic region are highlighted with black, gray, and open boxes, respectively. Amino acid numbering corresponds to the Env protein of the Petaluma FIV-14 isolate. (B) Amino acid sequence alignment of the V3 domains of FIV (Petaluma isolate) and HIV-1 (NL4-3 strain). The identical amino acids present at the same position in both sequences are indicated. Asterisks show the conservative amino acid changes between the FIV and HIV-1 V3 regions.