Torque modulates nucleosome stability and facilitates H2A/H2B dimer loss

Area of Science:

• Molecular Biology
• Biophysics
• Genetics

Background:

• Nucleosomes, the fundamental units of chromatin, exhibit a left-handed chirality due to DNA wrapping around core histones.
• This DNA superhelix chirality is hypothesized to be functionally significant in DNA supercoiling-dependent cellular processes like transcription and replication.
• The precise impact of torsional stress on nucleosome structure and stability remains largely uncharacterized.

Purpose of the Study:

• To investigate the effects of tension and torque on the structural behavior and stability of single nucleosomes.
• To elucidate the role of torsion in nucleosome unwrapping and histone dissociation.

Main Methods:

• Utilized the angular optical trapping technique to apply controlled tension and torque to single nucleosomes.
• Studied nucleosome behavior on the high-affinity 601-DNA positioning sequence.

Main Results:

• Torque exerted a moderate influence on the unwrapping of DNA from the nucleosome.
• Positive torque induced a significant dissociation of H2A/H2B histone dimers from the nucleosome.
• (H3/H4)₂ tetramers demonstrated high retention efficiency, independent of applied torsion.

Conclusions:

• Torsional stress has a differential impact on nucleosome components, primarily affecting histone dimer stability.
• These findings suggest a regulatory mechanism where torque influences histone exchange, potentially modulating chromatin dynamics during DNA replication and transcription.