FIG. 1.
Fusion of 89.6PI Env variants with CCR5/CXCR2 chimeras. Plasmids encoding R5 (A) and R5X4 (B) env genes derived from the 89.6PI quasispecies were transfected into QT6 cells and then mixed with 293T cells that were transfected with CD4 and the chimeric chemokine receptor. Fusion was determined by luciferase reporter gene expression as an indication of cytoplasmic mixing as described in Materials and Methods. The prototype R5X4 env derived from the 89.6 molecular clone was tested in parallel, along with the unrelated R5 prototype strain JRFL. The CCR5/CXCR2 recombinants were generated at the conserved Cys at residue 20, so that 5BBB contains the CCR5 N terminus on the background of CXCR2 while B555 contains the CXCR2 N terminus on the background of CCR5. Values represent luciferase reporter gene expression as a percentage of that seen with wild-type CCR5 for each env gene and represent means ± standard error of the mean for three independent experiments.