Three tryptophan residues interact with the DNA by recognizing the GAAA sequence in the IRF tryptophan pentad repeat (PS51507), a type I interferon gene that is induced by infection (IFN-α and IFN-β). One of the transcription factors that contributes to this activation is interferon regulatory factor I (IRF-1). The interferon consensus sequence (ICS) is a regulatory cis-element that is found upstream in the promoters of type I IFN and IFN-induced MHC class I genes. IRF-1 binds to this sequence. Interferon regulatory factor 2 (IRF-2) is a protein that also interacts with ICS.