The interferon regulatory factor (IRF) has a DNA-binding domain made up of five tryptophans. This is called the IRF tryptophan pentad repeat (PS00601). 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 interacts with ICS but does not function as an activator. Instead, it inhibits IRF-1 in specific situations.