Angle between DNA linker and nucleosome core particle regulates array compaction revealed by individual-particle...

Area of Science:

• Structural biology
• Chromatin organization
• Biophysics

Background:

• Nucleosome arrays exhibit complex conformational dynamics, challenging structural determination.
• Understanding chromatin compaction is crucial for gene regulation.

Purpose of the Study:

• To determine the 3D structures of nucleosome arrays using cryo-electron tomography (cryo-ET).
• To investigate the structural transitions during chromatin condensation under varying ionic strengths.
• To explore the role of histone H1 in chromatin organization.

Main Methods:

• Cryogenic electron tomography (cryo-ET) was employed to visualize individual nucleosomes and arrays.
• Nucleosome arrays were studied under varying ionic strengths to observe condensation dynamics.
• The influence of histone H1 on array structure was assessed.

Main Results:

• Low ionic strength resulted in irregular zig-zag conformations with loose packing.
• Increased ionic strength promoted intra-array compaction, but not the canonical 30-nm fiber.
• Histone H1 did not induce compaction; instead, it was associated with nucleosome invasion by foreign DNA.
• The DNA entry/exit angle relative to the nucleosomal disc is a key determinant of array structure.

Conclusions:

• The study provides insights into the initial stages of intra-array compaction.
• Findings suggest alternative roles for histone H1 in chromatin network construction.
• The DNA entry/exit angle is critical for dictating chromatin array conformation.