Alignment of the amino acid sequence of FeLV Env. Surface subunit (SU), transmembrane subunit (TM), receptor-binding domain (RBD), proline-rich region (PRR), and C domain of the Env protein are shown for FeLV-A 61E (49), FeLV-A clone 33 (41), and FeLV TG35-2 env clone (18) compared with FeLV TP2R. The variable regions, VRA, VRB, and PRR, are also shown by gray boxes. Dots indicate identical residues, and dashes indicate spaces that were introduced for the amino acid alignment. The Env sequences were aligned with the Genetyx program (Genetyx Corporation, Tokyo, Japan).