Two factor authentication: Asf1 mediates crosstalk between H3 K14 and K56 acetylation

Area of Science:

• Epigenetics and chromatin biology
• Molecular mechanisms of DNA repair
• Post-translational modifications of histones

Background:

• Histone acetylation regulates gene expression, DNA replication, and repair.
• Anti-silencing factor 1 (Asf1) is a histone chaperone involved in H3K56 acetylation.
• Asf1 interacts with Vps75 and Rtt109 in Saccharomyces cerevisiae for histone modification.

Purpose of the Study:

• To investigate the role of histone pre-acetylation and chaperones in driving specific H3K56 acetylation.
• To elucidate the mechanism of H3K56 acetylation by Rtt109-Vps75 in conjunction with Asf1.
• To identify functional regions within Asf1 that mediate crosstalk and influence Rtt109-Vps75 selectivity.

Main Methods:

• Utilizing singly acetylated histones to test the hypothesis of pre-acetylation-driven H3K56 acetylation.
• Biochemical assays to assess the interaction between Asf1, pre-acetylated histones, and the Rtt109-Vps75 complex.
• Site-directed mutagenesis of Asf1 to identify functional exosite regions and their impact on histone acetylation selectivity.

Main Results:

• Pre-acetylated H3K14ac/H4, in complex with Asf1, specifically drives H3K56 acetylation by Rtt109-Vps75.
• An acidic patch exosite in Asf1 was identified, and mutations altered Asf1-mediated crosstalk, affecting Rtt109-Vps75 selectivity.
• A proposed mechanism involves Gcn5 acetylation of H3K14, recruiting remodelers, enabling Asf1-H3K14ac/H4 complex acetylation at H3K56 by Rtt109-Vps75.

Conclusions:

• Histone pre-acetylation and chaperones like Asf1 are critical for the preferential and specific acetylation of H3K56.
• The identified Asf1 exosite plays a key role in mediating crosstalk and regulating the selectivity of the Rtt109-Vps75 acetyltransferase.
• The proposed mechanism integrates known genetic interactions and resolves conflicting biochemical data regarding H3K56 acetylation regulation.