IRF1, Interferon regulatory factor 1, is a member of the interferon regulatory transcription factor (IRF) family which regulates gene expression critical to immune response, hematopoiesis and proliferation. IRF-1 is a transcriptional activator for IFN-α, IFN-β, and IFN-γ stimulated genes. IRF1 is also a tumor suppressor transcription factor inducing apoptosis of tumorigenic cell lines. Recombinant human IRF1 was expressed in E.coli and purified by using conventional chromatography techniques.