FIG. 3.

Effects of mutations in the V3 crown and stem on tropism. (A) Effects of 2- and 4-amino-acid deletions in the V3 crown (residues 13 to 20) and stem (residues 9 to 12 and 21 to 25) on cell-cell fusion are shown. Percent fusion was calculated using luciferase activity normalized to R3A fusion on CD4⁺ CXCR4⁺ or CD4⁺ CCR5⁺ cells. The values are means plus standard errors of the mean (SEM). The data shown are the averages of three experiments. (B) Effects of deletions and alanine substitutions within the N-terminal side of the V3 stem (residues 9 to 12) on cell-cell fusion are shown. Percent fusion was calculated by using luciferase activity normalized to R3A fusion on CD4⁺ CXCR4⁺ or CD4⁺ CCR5⁺ cells. The values are means plus SEM. The data shown are the averages of three experiments. (C) Growth curves for infectious viruses containing the parental R3A and Δ9-12 Envs on SupT1 cells (CXCR4⁺ CCR5⁻) and SupCCR5 cells (CXCR4⁺ CCR5⁺) are shown. RT activity in culture supernatants was measured at the indicated time points. The results from one of two independent experiments are shown.