A Read/Write Mechanism Connects p300 Bromodomain Function to H2A.Z Acetylation

Area of Science:

• Epigenetics and Gene Regulation
• Histone Modifications
• Chromatin Biology

Background:

• Histone variant H2A.Z acetylation (H2A.Zac) is linked to active gene regulatory regions.
• While the Tip60 complex is implicated, other enzymes may also acetylate H2A.Z.

Purpose of the Study:

• To investigate the roles of p300 and Tip60 in H2A.Z acetylation.
• To explore the interplay between H2A.Z acetylation and H4 acetylation (H4ac).
• To understand how these acetylation patterns define chromatin states, particularly at enhancers.

Main Methods:

• In vitro enzymatic assays to assess H2A.Z acetylation by p300 and Tip60.
• Genetic inhibition of Tip60 to evaluate its in vivo role in H2A.Zac.
• Genomic analysis to map the overlap and exclusivity of H2A.Zac and H4ac at regulatory elements.
• Chromatin immunoprecipitation followed by sequencing (ChIP-seq) to identify genomic locations.

Main Results:

• p300 directly acetylates H2A.Z at multiple lysine residues.
• Tip60, while not efficient in vitro, is genetically required for H2A.Zac in cells.
• p300-mediated H2A.Zac is enhanced by its interaction with acetylated H4 (H4ac).
• H2A.Zac and H4ac exhibit significant genomic overlap at active promoters.
• Distinct chromatin features and transcriptional states at enhancers correlate with the presence or absence of H4ac and H2A.Zac.

Conclusions:

• Both Tip60 and p300 are key contributors to H2A.Z acetylation.
• p300 acts as a molecular bridge, linking H4 acetylation to H2A.Z acetylation.
• Differential acetylation signatures of H2A.Z and H4 can define enhancer states and influence gene expression.