FIG. 1.

Schematic of SIVmac239 gp120. Amino acids representing the entire primary sequence of SIVmac239 were drawn schematically based on the known disulfide bonds for HIV-1 (27) and the hypothetical disulfide bonds for SIV and HIV-2 (18). The variable regions were based on the designations defined by Choi et al. (8), and the V3 region corresponds to the analogous V3 loop of HIV-1. All 23 potential N-linked (N-X-S/T) glycosylation sites for SIVmac239 are indicated by the addition of a CHO symbol at the asparagine (N) residue. In addition, nine amino acid changes between the parental SIVmac239 and the recombinant SIV/17E-CL used to produce chimeric envelope proteins are designated at the appropriate residue with a square denoting the amino acid change (1).