Fig. 1.

Envelope glycoprotein characteristics of tier-categorized reference HIV-1 variants. The numbers of amino acids in the different regions of Env (from top to bottom: gp120, all variable regions, variable regions 1 and 2, variable region 1, and variable region 2) are depicted in the left panels, while the numbers of potential N-linked glycosylation sites (PNGS) are depicted in the right panels. The tier-categorized reference viruses are grouped according to their neutralization sensitivity, with tier 1 being the most neutralization sensitive and tier 3 the most neutralization resistant. Horizontal bars represent the mean values. The associations between numbers of amino acids or PNGS and neutralization resistance between viruses from the three tier groups were evaluated for statistical significance by the Jonckheere-Terpstra test and between two tier groups by Student's t test.