Abstract
Regulating gene expression is a complex process requiring the interaction of multiple transcription factors with their cognate recognition sequences. While these DNA-bound transcription factors are the primary drivers of gene expression, the capacity of a transcription factor to alter gene expression is tempered by its association with a host of coregulatory proteins that are recruited to the DNA-bound transcription factor. We have developed a novel approach to isolate large complexes of proteins associated with the DNA-bound estrogen receptor alpha (ERalpha) using an agarose-based electrophoretic mobility shift assay (EMSA). This method should be readily adapted to a variety of cultured cell lines, DNA sequences, and transcription factors and has the potential to provide valuable information about a wide variety of regulatory proteins involved in influencing gene expression.