The Saccharomyces cerevisiae Swi/Snf Complex Can Catalyze Formation of Dimeric Nucleosome Structures in Vitro

Abstract

The Swi/Snf chromatin-remodeling complexes, human BAF/PBAF and yeast RSC, can catalyze formation of stably altered dimeric forms of nucleosomes. However, the ability to create remodeled dimers has not yet been reported for the Saccharomyces cerevisiae Swi/Snf complex. Despite its similarity with the other Swi/Snf proteins, the yeast Swi/Snf complex features certain structural and functional differences. This raises the question of whether ySwi/Snf can in fact catalyze formation of dimeric nucleosomes. Dimer formation was proposed to have a specific impact on chromatin regulatory effects. Thus, the answer to the above question may be helpful in clarifying the ySwi/Snf functions in vivo and generalizing the notions of the regulatory principles of Swi/Snf family proteins. Here we describe ySwi/Snf-catalyzed formation of nucleosome dimers using mono- and dinucleosome templates assembled from purified histones and DNA of the high-affinity (601) nucleosome positioning sequence. We evaluated effects of nucleosome template geometry on the formation of altered dimers and assayed formation of altered nucleosome pairs on reconstituted dinucleosomes.