Structural insights into histone binding and nucleosome assembly by chromatin assembly factor-1

Area of Science:

• Molecular Biology
• Epigenetics
• Structural Biology

Background:

• Chromatin inheritance requires new nucleosome assembly after DNA replication.
• Chromatin assembly factor-1 (CAF-1) is crucial for this process.
• The precise mechanism of CAF-1's histone binding and nucleosome assembly remains unclear.

Purpose of the Study:

• To elucidate the structural basis of histone binding by CAF-1.
• To understand CAF-1's role in the initial stages of nucleosome assembly.
• To investigate the structural intermediates involved in chromatin replication.

Main Methods:

• X-ray crystallography to determine the structure of human CAF-1 without histones.
• Cryo-electron microscopy to visualize CAF-1 in complex with histones H3 and H4.
• Structural analysis of CAF-1-histone complexes to understand binding modes and assembly intermediates.

Main Results:

• The crystal structure of human CAF-1 was determined.
• The cryo-EM structure revealed CAF-1 binding to a histone H3-H4 heterodimer via its p60 and p150 subunits.
• A dimeric CAF-1-H3-H4 supercomplex was observed, suggesting a pathway for tetramer formation.
• CAF-1 was shown to facilitate right-handed DNA wrapping of H3-H4 tetramers, indicating DNA's role in tetramer formation.

Conclusions:

• CAF-1 directly binds histone H3-H4 heterodimers.
• The observed supercomplex suggests a mechanism for H3-H4 tetramer formation during chromatin replication.
• DNA plays a role in H3-H4 tetramer formation, leading to a right-handed nucleosome precursor.