Inhibition of HIV-1 infectivity by APOBEC3 proteins and ability of Vif proteins to overcome inhibition. (A) Viral stocks were generated by cotransfecting 293T cells with increasing amounts of APOBEC3 expression plasmids (0, 75, 150, and 300 ng in a 24-well plate) and fixed amounts of HIV-1 GagPol (150 ng), HIV-1 GFP vector (150 ng), and VSV-G (100 ng) expression plasmids and Vif or a control (150 ng) expression plasmid. Infectivity was measured by using human CEMx174 T cells as target cells. Infected cells were enumerated by fluorescence-activated cell sorter analysis. Results representative of two experiments are shown. huA3G, huAPOBEC3G; agmA3G, agmAPOBEC3G; rhA3G, rhAPOBEC3G; rhA3F, rhAPOBEC3F; rhA3H, rhAPOBEC3H; rhA3B, rhAPOBEC3B; rhA3DE-I, rhAPOBECDE-I; rhA3DE-II, rhAPOBECDE-II; rhA3C, rhAPOBEC3C; agmA3H, agmAPOBEC3H. (B) Transfected 293T cells were lysed, and expression of each APOBEC3 protein in the absence or presence of the various Vif proteins, as indicated, was monitored by immunoblotting with an antibody against myc. Each group of three lanes represents cells transfected with decreasing amounts (300, 150, and 75 ng), from left to right, of each APOBEC3 expression plasmid.