Virus infection induces the assembly of coordinately activated transcription factors on the IFN-β enhancer in vivo

We have identified a virus-activated factor (VAF) that binds to a regulatory element shared by different virus-inducible genes. We provide evidence that VAF contains two members of the interferon regulatory factor (IRF) family of transcriptional activator proteins (IRF-3 and IRF-7), as well as the transcriptional coactivator proteins p300 and CBP. Remarkably, VAF, as well as recombinant IRF-3 and IRF-7 proteins, binds very weakly to the interferon-beta (IFN-beta) gene promoter in vitro. However, in virus-infected cells, both proteins are recruited to the endogenous IFN-beta promoter as part of a protein complex that includes ATF-S/c-Jun and NF-kappa B. These observations provide a unique example of the coordinate activation of multiple transcriptional activator proteins and their highly cooperative assembly into a transcriptional enhancer complex in vivo.