HIV Type 1 Viral Infectivity Factor and the RUNX Transcription Factors Interact with Core Binding Factor β on Genetically Distinct Surfaces

Human immunodeficiency virus type 1 (HIV-1) requires the cellular transcription factor core binding factor subunit beta (CBF beta) to stabilize its viral infectivity factor (Vif) protein and neutralize the APOBEC3 restriction factors. CBF beta normally heterodimerizes with the RUNX family of transcription factors, enhancing their stability and DNA-binding affinity. To test the hypothesis that Vif may act as a RUNX mimic to bind CBF beta, we generated a series of CBF beta mutants at the RUNX/CBF beta interface and tested their ability to stabilize Vif and impact transcription at a RUNX-dependent promoter. While several CBF beta amino acid substitutions disrupted promoter activity, none of these impacted the ability of CBF beta to stabilize Vif or enhance degradation of APOBEC3G. A mutagenesis screen of CBF beta surface residues identified a single amino acid change, F68D, that disrupted Vif binding and its ability to degrade APOBEC3G. This mutant still bound RUNX and stimulated RUNX-dependent transcription. These separation-of-function mutants demonstrate that HIV-1 Vif and the RUNX transcription factors interact with cellular CBF beta on genetically distinct surfaces.