YY1 is a ubiquitously distributed transcription factor belonging to the GLI-Kruppel class of zinc finger proteins. This protein is involved in repressing and activating a diverse number of promoters. YY1 may direct histone deacetylases and histone acetyltransferases to a promoter in order to activate or repress the promoter, thus implicating histone modification in the function of YY1. Recombinant human YY1 protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.