Early studies indicated that SWI/SNF complexes are targeted to their sites of action by simply being recruited by a DNA binding protein, such as SWI5, which normally is located in the cytoplasm and moves into the nucleus upon treatment with mating factor (29). In this way, SWI5 is both a signaling protein and a transcription factor. From these studies, it was concluded that in yeast, the SWI5 transcription factor recruits the SWI/SNF complex to its site on the HO endonuclease gene. After recruitment, the complex stays in this location, whereas the transcription factor can move to another location. This mechanism provided an easy understanding of the origin of specificity of binding and is well suited to yeast, where most DNA is accessible and few genes are epigenetically suppressed.
