ATP-dependent and independent mechanisms of regulating chromatin states

Abstract Chromatin provides a means to compartmentalize the genome into active (euchromatin) and heritably repressed (heterochromatin) states. Changes in these states accompany changes in cellular differentiation and are essential for stabilizing cellular identity. Both types of chromatin states are maintained and rearranged by the combined action of diverse ATP-dependent chromatin remodeling motors and specific chromatin binding proteins. The proposed work is aimed at studying the core mechanisms of some of the major chromatin regulators to achieve a better understanding of how their activities are regulated in vivo. Using a variety of biophysical approaches, we have uncovered that ATP-dependent remodelers use sophisticated auto- inhibition based mechanisms. We have also uncovered hexasomes as the preferred substrate for one type of conserved remodeler. These findings provide a biophysical basis for further probing why different remodelers have different biological roles. We had previously discovered phase-separation behavior by HP1 proteins, the core components of heterochromatin. Since then, we have uncovered that phase-separated heterochromatin reconstituted in a test-tube possesses several of the biophysical properties attributed to heterochromatin in cells. Here we will build on these new discoveries to ask the following questions: 1. Why are their differences in mechanism between remodelers from different classes? 2. How does action of remodelers at the nucleosome scale impact chromatin at bigger scales? 3. What is the role of phase-separation in heterochromatin regulation?