Vif efficiently rescues viral infectivity. HeLa cells were transfected with the vif-defective proviral vector pNL4-3vif(-) together with pNL-A1 and pHIV-APO3G at 1:1, 2:1, or 5:1 molar ratios. Cell lysates and purified, concentrated viral extracts were analyzed by immunoblotting using antibodies to APOBEC3G (APO3G), Vif (MAb #319), or an HIV-positive human serum for the identification of viral capsid protein (CA). Virus-containing, filtered supernatants were normalized for equal reverse transcriptase activity and used for the infection of the LuSIV indicator cell line . Virus-induced luciferase activity was measured 24 hr after infection as described in Methods. Relative light units (RLU), which are directly proportional to the infectivity of the viruses, are shown. Error bars reflect standard deviations from duplicate experiments.