FIG 2.

Determinants for iMac239 Env CD4 independence in cell-cell fusion and viral replication assays. (A) Fusion activity on rhesus CCR5 in the presence or absence of rhesus CD4 is shown for SIVmac239 Envs containing the indicated single mutations from iMac239. Data from 3 experiments plus SEM are shown as described for Fig. 1B. Two-way analysis of variance (ANOVA) with multiple comparisons was used to determine significance. (B) Replication of SIVmac239-based viruses bearing the indicated Envs is shown in CD4⁺ SupT1/RhR5 (left) and CD4⁻ BC7/RhR5 (right) cells. Four changes in gp120 are sufficient to confer CD4-independent replication. A virus with D178G alone was unable to replicate in either cell type but was rescued for replication in SupT1 by H224Q. RT activity was measured at the indicated time points. Results from a representative experiment are shown.