ART4 and infection: The HIV-1JR-FL Env(+)Δ712 FT glycoprotein did not detectably support virus entry into Cf2Th-CD4/CCR5 cells in this assay, whereas the Env(+)Δ712 FTmut glycoprotein mediated infection at a level 37% of that observed for the Env(+)Δ712 glycoprotein (Fig. 5g).