FIG. 1.

The HIV-1 env gene. (A) The HIV-1 env gene produces surface (gp120) and transmembrane (gp41) glycoprotein subunits from a precursor molecule through posttranslational proteolytic cleavage. The five variable regions of gp120 and a conserved CD4 binding site are indicated. The enlarged inset depicts the major structural domains of gp41 (not to scale). Amino acid alignments of the N-terminal (B) and C-terminal (C) heptad repeat regions are shown for HXB2 (used as the reference sequence), NL4.3, and JRFL. Residues that are identical to the HXB2 sequence are indicated by dashes, and substitutions are indicated by the amino acid letter. (B) The T-20 interaction site in HR1, residues 36 to 38, is shown in bold. (C) The corresponding positions of T-20 and T-649 in HR2 are indicated above the alignments. Both peptides are identical to the HXB2 sequence.