APOBEC3 proteins are antiviral host factors for a wide variety of retroviruses. HlV-1 Vif overcomes the antiviral activity of APOBEC3G by ubiquitinating the protein. In this study, we examined the ability of Vif to antagonize other family members of APOBEC3 proteins, together with its mechanism. Using HIV infectivity, virion incorporation, immunoprecipitation, and in vitro ubiquitin conjugation assays, we show that the ability of Vif to inhibit antiviral activity of APOBEC3 proteins positively correlates with its ability to bind and ubiquitinate these proteins by a Vif-Cullin5-ElonginB-ElongmC (Vif-BC-Cul5) complex. These results suggest that Vif exhibits its anti-APOBEC3 activity by the ubiquitin ligase activity of the Vif-BC-Cul5 complex. (C) 2005 Elsevier Inc. All rights reserved.