Liquid-liquid phase
separation (LLPS) of proteins and DNA has recently emerged as a possible
mechanism underlying the dynamic organization of chromatin. We herein report
the role of DNA quadruplex folding in liquid droplet formation via LLPS induced
by interactions between DNA and linker histone H1 (H1), a key regulator of
chromatin organization. <a>Fluidity measurements inside the
droplets, binding assays using G-quadruplex-selective probes, and structural
analyses based on circular dichroism demonstrated that quadruplex DNA
structures, such as the G-quadruplex and i-motif, promote droplet formation
with H1 and decrease molecular motility within droplets. </a><a></a><a></a><a>The dissolution of the droplets in the
presence of additives and the LLPS of the DNA structural units indicated that
in addition to electrostatic interactions between the DNA and the intrinsically
disordered region of H1, π-π stacking between quadruplex DNAs could potentially
drive droplet formation, unlike in the electrostatically driven LLPS of duplex
DNA and H1. According to phase diagrams of anionic molecules with various
conformations, the high LLPS ability associated with quadruplex folding arises
from the formation of interfaces consisting of organized planes of guanine
bases and the side surfaces with high charge density. </a>Given
that DNA quadruplex structures are well documented in heterochromatin regions,
it is imperative to understand the role of DNA quadruplex folding in the
context of intranuclear LLPS.<br>
G-quadruplex DNA inhibits unwinding activity but promotes liquid–liquid phase separation by the DEAD-box helicase Ded1p