FIG. 4.

Env cytoplasmic tail length affects MLV specificity and infectivity in pseudotyped particles. Infectivity assays were performed by transfecting 293FT cells and 48 h later transferring viral media onto 293T mCAT-1 cells. (A) MLV GagPol with a fluorescent MLV genome reporter or (B) an HIV-1 provirus with a GFP reporter was co-transfected with each Env construct into 293FT cells. (C) Competition assays were performed as described above, but both proviral components were co-transfected with each Env construct into each well. (D) Relative infectivity was calculated for each Env treatment by first calculating the ratio MLV IU (infectious units) per ml to HIV-1 IU per ml and then each value was normalized by the ratio of VSV Env with MLV core to HIV-1 core. A representative experimental result from one of three replicates is shown for parts A and B. Means and ±SD from all three experiments are reported in Table 1.