Interferon regulatory factor 1 (IRF-1) is an essential factor involved in the regulation of type I interferon (IFN) and IFN-inducible genes, The protein consists of 329 amino acids that are highly conserved from mouse to human, Similar to other transcription factors, the protein is modular in nature with a basic N-terminal region involved in DNA binding and an acidic C-terminal region required for activation, We report here the expression, purification and co-crystallization of the minimal N-terminal region of IRF-1 involved in DNA binding (amino acids 1-113) with a 13 bp DNA fragment from the IFN-beta promoter, The crystals diffract to at least 3.0 Angstrom in resolution and belong to space group R3 with unit cell parameters of a=b=84.8 Angstrom, c = 203.7 Angstrom. (C) 1997 Federation of European Biochemical Societies.