FIG 1.

Replication and fusion of CD4-independent variants of SIVmac239. (A) Replication of parental SIVmac239 and an uncloned CD4-independent viral swarm is shown in CD4⁺ SupT1/RhR5 cells (left) and CD4⁻ BC7/RhR5 cells (right), each of which stably expressed rhesus CCR5. RT, reverse transcriptase activity. (B) Fusion activity of SIVmac239 and four iMac239 env clones on QT6 cells using a cell-cell fusion assay. For each env gene, the level of CD4-independent fusion on rhesus CCR5 is shown as a percentage of fusion (luciferase activity) in the presence of rhesus CD4. Background fusion levels on cells expressing GFP only were subtracted. The data shown are the means of three experiments plus the standard errors of the means (SEM). (C) Growth curves in CD4-negative, BC7/RhR5 cells are shown for wild-type (WT) SIVmac239, the iMac239 viral swarm, and four recombinant SIVmac239-based viruses bearing the indicated iMac239 env clones. RT activity in culture supernatants was measured at the indicated time points. Results from a representative experiment are shown.