Nucleosome conformation dictates the histone code

Area of Science:

• Epigenetics and Molecular Biology
• Chromatin Biology
• Gene Regulation

Background:

• Histone post-translational modifications (PTMs) are crucial for chromatin regulation.
• The 'histone code' hypothesis suggests PTMs are recognized by protein domains (reader domains) on chromatin-associated proteins (CAPs).
• Previous studies often used simplified models like isolated reader domains and histone peptides.

Purpose of the Study:

• To investigate the role of nucleosome context in the interaction between reader domains and histone PTMs.
• To determine if the specificity of the BPTF tandem reader (PHD finger and bromodomain) for histone PTMs is influenced by the nucleosome structure.
• To refine the 'histone code' concept by considering higher-order chromatin factors.

Main Methods:

• In vitro binding assays using isolated reader domains and histone peptides.
• Nucleosome reconstitution and biochemical assays to assess BPTF tandem reader binding specificity.
• Cellular context experiments to validate in vitro findings.

Main Results:

• The interaction of the BPTF PHD finger and bromodomain with histone PTMs is dependent on the nucleosome context.
• The tandem reader selectively binds to nucleosomes with specific combinations of PTMs (H3K4me3 with H3K14ac or H3K18ac).
• This nucleosome-specific binding is not predictable from isolated peptide assays and is recapitulated in cells.

Conclusions:

• The 'histone code' needs refinement to incorporate nucleosome context and higher-order chromatin factors.
• Histone tail accessibility and reader domain binding potential are influenced by the nucleosome structure.
• Future research should interrogate histone codes at the nucleosome level for a comprehensive understanding of epigenetic regulation.