Fig. 4.

Locations of the amino acid positions associated with in utero mother-to-child transmission. The HIV-1 JR-FL gp120 core (PDB 2B4C) is displayed in white in a cartoon format complexed with a fragment of the CD4 ligand, which is drawn in gray in a space-filling format. Four of the 5 amino acids correlated with in utero transmission are colored yellow (position 6, in the signal peptide, is not included in the structure); the two positions with evidence of purifying selection during in utero transmission are displayed in red. Amino acid positions are indicated in white text.