Restriction factors, such as the retroviral complementary DNA deaminase APOBEC3G, are cellular proteins that dominantly block virus replication. The AIDS virus, human immunodeficiency virus type 1 (HIV-1), produces the accessory factor Vif, which counteracts the host's antiviral defence by hijacking a ubiquitin ligase complex, containing CUL5, ELOC, ELOB and a RING-box protein, and targeting APOBEC3G for degradation. Here we reveal, using an affinity tag/purification mass spectrometry approach, that Vif additionally recruits the transcription cofactor CBF-β to this ubiquitin ligase complex. CBF-β, which normally functions in concert with RUNX DNA binding proteins, allows the reconstitution of a recombinant six-protein assembly that elicits specific polyubiquitination activity with APOBEC3G, but not the related deaminase APOBEC3A. Using RNA knockdown and genetic complementation studies, we also demonstrate that CBF-β is required for Vif-mediated degradation of APOBEC3G and therefore for preserving HIV-1 infectivity. Finally, simian immunodeficiency virus (SIV) Vif also binds to and requires CBF-β to degrade rhesus macaque APOBEC3G, indicating functional conservation. Methods of disrupting the CBF-β-Vif interaction might enable HIV-1 restriction and provide a supplement to current antiviral therapies that primarily target viral proteins.
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Acknowledgements We thank members of the Krogan, Gross and Harris laboratories for comments,J.R.Johnson for mass spectrometry,B.Leonard for sharing unpublished data,M.Shalesforhelpwithfigures,andB.Chesebro,D.Gabuzda,J.Lingappa,M.Malim, K. Wehrly, X. F. Yu, A. Bullock, B. Schulman and the AIDS Research and Reference Reagent Program for reagents. This research was funded by grants from QB3 at University of California, San Francisco, and the National Institutes of Health (P50 GM082250, P01 AI090935 and P50 GM081879 to N.J.K.; U54 RR022220 to A.S.; R01 AI064046 and P01 GM091743 to R.S.H.; P50 GM082250 to J.D.G. and C.S.C.; P41RR001614 and P50GM081879toA.B.). N.J.K.isa SearleScholar and a Keck Young Investigator.