A central question in the analysis of transcription factors in eukaryotes is how these DNA-binding proteins function with a chromatin template. The binding of factors to chromatin templates occurs readily in vivo as well as in vitro in the presence of factors in crude chromatin assembly extracts. Yet, on the other hand, biochemical experiments with purified or partially purified nucleosomal templates indicate that the packaging of DNA into chromatin is often, but not always, an impediment to the binding of proteins to DNA. It is therefore reasonable to consider that there may be specialized factors that can act to facilitate the function of DNA-binding proteins with chromatin. In this regard, recent work from a number of laboratories has led to the postulate that SWI2/SNF2 and related proteins can function to destabilize nucleosome structure and thereby to facilitate the binding of transcription factors to chromatin (reviewed in