Construction of the ACH-envelope clones. (A) ACH.75, ACH.95, and ACH.195 contain the env gene of the HTE mutants²⁰  between an SphI site and an NsiI site in the ACH molecular clone. The point mutants are designated by the wild-type amino acid, the position (in comparison to initiator methionine), and the mutant amino acid. SU indicates surface protein; TM, transmembrane protein; CD, cytoplasmic domain. (B) HTLV-1 SU protein. Schematic summary of functional domains of SU.^10,14-22  The position of amino acid mutants examined in this study is indicated in bold.