The Yin Yang 1 protein is a zinc finger transcription factor involved in the regulation of diverse cellular processes through DNA and protein-protein interactions. Here we present an improved method for the expression and purification of the human full-length YY1 protein from Escherichia coli. The protein was first purified using denaturing conditions, refolded using optimized conditions and then purified using a DNA-affinity column to >= 95% purity; this process provided a high final yield and highly active protein. The protein was active in EMSA and the fluorescence anisotropy assays. The protein retained its full activity and its initial concentration for several months when stored at -80 degrees C. Thus, we have obtained YY1 protein with levels of activity and concentration that are suitable for spectroscopic and other biochemical studies. (c) 2011 Elsevier Inc. All rights reserved.