Assessing the Effect of Chromatin-Binding Enzymes on Condensed Chromatin with Optical Tweezers

The formation of biomolecular condensates in vitro and in vivo has become an increasingly important subject of studies. One particular area of interest is the phase separation of chromatin in the nucleus. However, the interplay of condensed chromatin and chromatin-binding enzymes has barely been studied as of now. Here, we show an optical tweezer-based assay that uses controlled fusion of two condensates to probe the effect of enzymes, such as chromatin remodeling motor proteins, on the fluidity of condensates. The assay provides a powerful tool that enables the study of if and how chromatin-enzyme interactions alter biophysical properties in these dense chromatin condensates.