STAT1, also known as STAT91, is a member of the STAT protein family. In response to cytokines and growth factors, STAT family members are phosphorylated by the receptor associated kinases, and then form homo- or heterodimers that translocate to the cell nucleus where they act as transcription activators. STAT1 is activated by peptide hormones, growth factors and cytokines, particularly cytokines of the interferon family. Recombinant human STAT1 protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.