SMAD4 belongs to the SMAD family of proteins that mediate signal transduction by the TGF-beta/activin/BMP-2/4 cytokine superfamily from receptor Ser/Thr protein kinases at the cell surface to the nucleus. SMAD4 promotes the binding of the SMAD2/SMAD4/FAST-1 complex to DNA and provides the function of activation required for SMAD1 or SMAD2 to stimulate transcription and may also act as a tumor suppressor. Recombinant SMAD4 protein was expressed in E.coli and purified by using conventional chromatography techniques.