Histone H3 tail charge patterns govern nucleosome condensate formation and dynamics

Area of Science:

• Molecular Biology
• Biophysics
• Genetics

Background:

• Emerging models propose that nuclear organization involves chromatin forming distinct microenvironments via phase separation.
• Chromatin architecture is intrinsically linked to nucleosome organization and regulated by histone post-translational modifications.

Purpose of the Study:

• To investigate how histone modifications influence nucleosome phase behavior.
• To understand the role of histone H3 tail charge distribution in regulating nucleosome phase separation and condensate properties.

Main Methods:

• Systematic alteration of charge distribution within the histone H3 tail.
• Microscopy-based assays and microrheology to assess nucleosome condensate properties.
• Nuclear magnetic resonance (NMR) relaxation experiments to probe histone tail dynamics.
• Computational simulations to model nucleosome phase behavior.

Main Results:

• Specific regions (terminal and central) of the H3 tail differentially modulate the phase boundary and viscosity of nucleosome condensates.
• Histone H3 tails exhibit dynamic mobility within condensates, which correlates with condensate viscosity.
• The number, identity, and spatial arrangement of basic residues in the H3 tail are critical regulators of nucleosome phase separation.

Conclusions:

• Nucleosome phase separation is actively regulated by the intrinsic properties and modifications of the histone H3 tail.
• These findings support a model where nucleosomes actively shape local chromatin microenvironments through phase separation.
• Provides new insights into the 'histone language' governing chromatin condensates and nuclear organization.