Mutual Antagonism Between PRC1 Condensates and SWI/SNF in Chromatin Regulation.

Opposing activities of conserved chromatin regulatory complexes, such as the Polycomb Repressive Complex 1 (PRC1) and the activating chromatin remodeler SWI/SNF play critical roles in regulating gene expression during development and differentiation. The mechanisms by which these complexes compete to regulate chromatin states remain poorly understood. We combine single-molecule analysis and genomic approaches in cultured cells to demonstrate that the condensate-forming properties of PRC1 play an important role in excluding SWI/SNF from chromatin. Consistently, PRC1 compositions with a higher propensity for condensate formation are more effective in preventing SWI/SNF binding. Conversely, SWI/SNF-bound chromatin significantly reduces PRC1 binding and subsequent condensate formation. Notably, SWI/SNF can suppress PRC1 condensate formation in an ATP-hydrolysis independent manner. We propose that the condensate properties of different PRC1 compositions drive mutual PRC1-SWI/SNF antagonism to properly balance these competing regulatory activities during development.