# A Site-Specific Self-Association of a Protein Hub Drives Its Phase Separation

## TL;DR

This study shows how a specific protein interaction drives phase separation in cells, forming structures that respond to stress.

## Contribution

The discovery of a site-specific self-association mechanism driving WDR5 phase separation is novel.

## Key findings

- WDR5 self-associates via its N-terminal region and a multitasking site to form liquid droplets.
- WDR5 forms nuclear puncta in mammalian cells under osmotic stress.
- RNA modulates WDR5 phase separation and nuclear puncta formation.

## Abstract

Liquid–liquid
phase separation (LLPS) is pivotal in generating
membraneless organelles and assembling cellular inclusions. Interactions
mediated by RNA and intrinsically disordered regions of proteins are
ubiquitous mechanisms that drive their LLPS. Here, we identify that
a site-specific interaction stimulates the LLPS of WDR5, a chromatin-associated
protein hub. Our study proves that WDR5 undergoes self-association
between its N-terminal intrinsically disordered region and a multitasking
binding site. This mechanism facilitates the formation of liquid droplets
in a cell-free environment. Notably, WDR5 undergoes phase separation
in mammalian cells, forming nuclear puncta (NP) in response to osmotic
stress. Further, nuclear WDR5 condensates encompass a critical oncoprotein
transcription factor, MYC, and WDR5-binding RNA under hyperosmotic
conditions. Our findings suggest that RNA modulates WDR5 phase separation
and influences nuclear puncta formation, potentially serving as a
general stress response mechanism. These outcomes illuminate a distinctive
mechanochemical signaling process, highlighting the functional interplay
among WDR5, RNA, and MYC at the chromatin level, particularly during
osmotically induced LLPS.