FIG. 4.

OptiPrep gradient analysis of extracellular Vif from HXB2NEO H9 cells. Extracellular supernatants were pelleted through a 20% sucrose cushion and then subjected to velocity gradient centrifugation in 6 to 18% iodixanol. Fractions were collected, with fraction 1 referring to the top of the gradient, as indicated; the protein profiles were analyzed by immunoblotting with an HIV-1-positive serum (A), anti-p6^Gag serum (B), and anti-Vif serum (C). Aliquots of OptiPrep gradient fractions were stained with Coomassie blue (D) and assayed for RT activity (E) and infectivity on SupT1 cells by syncytium formation (F).