# H2A.Z and H3:K56Q Affect Transcription Through Chromatin and Yeast FACT-Dependent Nucleosome Unfolding

## TL;DR

This study explores how specific histone modifications and variants help reorganize nucleosomes to allow transcription initiation in yeast.

## Contribution

The study reveals that H2A.Z and H3:K56Q work with FACT to unfold nucleosomes and promote histone eviction, enhancing transcription.

## Key findings

- H3:K56Q alone or with H2A.Z promotes Nhp6-dependent nucleosome unfolding by FACT.
- Unfolding of variant nucleosomes leads to histone eviction from DNA.
- H2A.Z with or without H3:K56Q supports transcription as effectively as FACT on canonical nucleosomes.

## Abstract

Yeast +1 nucleosomes positioned at transcription start sites must be reorganized to allow transcription initiation. Nucleosome reorganization involves multiple factors including histone chaperone FACT (FAcilitates Chromatin Transcription), histone acetylation, and histone variant H2A.Z; however, the mechanism of this process is not fully understood. Here we investigated nucleosome unfolding in the presence of these factors by combining biochemical assays with single-particle Förster resonance energy transfer (spFRET) microscopy. The presence of the H3:K56Ac mimic (H3:K56Q) alone or together with H2A.Z (but not H2A.Z alone) facilitates the Nhp6-dependent unfolding of nucleosomes by FACT. In contrast to canonical nucleosomes, the unfolding of nucleosomes with the studied variant histones promotes the eviction of core histones from nucleosomal DNA. Furthermore, H2A.Z alone or in synergy with H3:K56Q facilitates transcription through a nucleosome as efficiently as FACT facilitates transcription through canonical nucleosomes. The data suggest that FACT, together with H3:K56 acetylation and H2A.Z, unfold promoter nucleosomes and participate in the eviction of histones to increase the accessibility of the transcription start site, thereby stimulating transcription initiation and possibly early elongation.