Book Description
Recruitment of the yeast Silencing Information Regulator complex (SIR complex) to regions of silenced heterochromatin is essential for maintaining a transcriptionally-repressed chromatin environment. Distinct boundaries exist to demarcate silenced heterochromatin from facultative heterochromatin and yet little is known regarding how this boundary is established or maintained. In this study, we observed linker DNA-independent binding of Sir3 to the nucleosome. We then examined the interactions of Sir3 with the ATP-dependent chromatin remodeling complexes ISW2, ISW1a, INO80, ISW1b, and SWI/SNF. In the cell, the interplay between these remodeling complexes, the SIR complex, and other chromatin associated proteins likely plays a regulatory function to maintain silencing throughout a particular region and restrict the spreading of this silenced state to adjacent chromatin regions. Investigations of the silent mating type locus in yeast may provide important clues toward understanding global transcriptional silencing mechanisms in higher eukaryotes. We demonstrate that Sir3 has no inhibitory effect upon remodeling by any of the complexes examined in this study and that Sir3 does not prevent ISW2 or SWI/SNF from binding the nucleosome.