Incorporation of APO3G inversely correlates with viral infectivity. Cell free virus particles from figure 1 were normalized for reverse transcriptase activity and used to infect LuSIV indicator cells. Virus-induced activation of luciferase was determined 24 h later in a standard luciferase assay as described in Methods. Mock transfected cells were included as a negative control (mock). Vif-defective virus produced in the absence of A3G served as positive control (Ctrl) and was defined as 100%. Infectivities of the A3G-containing virus preparations were calculated relative to the A3G-negative virus. Error bars reflect standard error calculated from duplicate infections.