(A) Jurkat and HeLa cells stably expressing the ALV-A receptor (TvA) or TagRFP-657, as indicated, were fused by treatment with PEG and transduced with ALV-A Env-pseudotyped HIV-1NL4-3-GFP, or with isogenic vector bearing the SIVMAC239 CA1-202. Shown are flow cytometry dot plots obtained 48 hrs post-transduction. HeLa-TagRFP-657 cells are only permissive to infection with ALV-A Env-pseudotyped vectors after fusion with Jurkat-TvA. Infected heterokaryons were visualized as GFP and TagRFP-657 double-positive cells. As a positive transduction control, TagRFP-657 and TvA were also co-expressed in HeLa cells, as indicated. The percentage of transduced cells are indicated. (B) Bar graph showing the infectivity of the SIVMAC239 CA1-202-bearing vector relative to the isogenic vector bearing HIV-1 CA, for the HeLa, Jurkat and heterokaryons. Data from the flow cytometry data shown in A, and two repeat experiments, is shown with the standard deviation.