Function: Specifically binds to the upstream regulatory region of type I IFN and IFN-inducible MHC class I genes (the interferon consensus sequence (ICS)) and represses those genes. Also acts as an activator for several genes including H4 and IL7. Constitutively binds to the ISRE promoter to activate IL7. Involved in cell cycle regulation through binding the site II (HiNF-M) promoter region of H4 and activating transcription during cell growth. Antagonizes IRF1 transcriptional activation. PTM: Acetylated by CBP/ p300 during cell-growth. Acetylation on Lys-75 is required for stimulation of H4 promoter activity. The major sites of sumoylation are Lys-137 and Lys-293. Sumoylation by SUMO1 increases its transcriptional repressor activity on IRF1 and diminishes its ability to activate ISRE and H4 promoter. Similarity: Belongs to the IRF family. Contains 1 IRF tryptophan pentad repeat DNA-binding domain. Tissue specificity: Expressed throughout the epithelium of the colon. Also expressed in lamina propria.