The Histone Chaperone FACT Contributes to DNA Replication-Coupled Nucleosome Assembly

Area of Science:

• Molecular Biology
• Epigenetics
• Chromatin Biology

Background:

• DNA replication-coupled (RC) nucleosome assembly is crucial for epigenetic inheritance and genomic stability.
• Histone chaperones mediate RC nucleosome assembly, but their mechanisms are not fully understood.
• The FACT (facilitates chromatin transactions) complex, comprising Spt16 and Pob3, is a known histone chaperone.

Purpose of the Study:

• To elucidate the role of the FACT complex in RC nucleosome assembly.
• To investigate the interaction of FACT with other histone chaperones involved in nucleosome deposition.
• To determine how post-translational modifications, like H3K56 acetylation, influence FACT's function in RC nucleosome assembly.

Main Methods:

• Characterization of a mutant Spt16 allele (spt16-m) with impaired H3-H4 binding.
• Analysis of synthetic genetic interactions between spt16-m and mutations in other histone chaperone genes (CAF-1, Rtt106).
• Co-immunoprecipitation assays to detect physical association between FACT and Rtt106, and assessment of H3K56 acetylation's effect on this interaction.

Main Results:

• The spt16-m mutation impairs H3-H4 binding and deposition onto DNA during RC nucleosome assembly.
• spt16-m exhibits synthetic defects with CAF-1 and Rtt106, indicating functional collaboration.
• FACT physically associates with Rtt106, and this interaction is modulated by H3K56 acetylation.

Conclusions:

• The FACT complex plays a direct role in promoting the deposition of newly synthesized H3-H4 histones during RC nucleosome assembly.
• FACT functions in concert with CAF-1 and Rtt106, suggesting a coordinated mechanism for efficient nucleosome formation.
• H3K56 acetylation is an important regulatory mark that modulates the interaction between FACT and Rtt106, fine-tuning nucleosome assembly.