FIG. 4.

Fusion activity of HIV and HIV-MuLV chimeric Env proteins. Env proteins were expressed in HeLa cells using the vaccinia virus T7 expression system. HeLa cells were infected by recombinant virus VTF7-3 for 1 h and then transfected with DNA constructs encoding the Env proteins. At 12 h posttransfection, HeLa cells were overlaid with HeLa T4 cells (obtained from the NIH AIDS Research and Reference Reagents Program) which express CD4 and fusin. Cell fusion pictures were taken at 8 h after overlay of HeLa cells under a Nikon microscope. (a) Mock transfection; (b) full-length HIV Env; (c) H-Menv; (d) H-MenvR-.