Fragile nucleosomes are essential for RNA Polymerase II to transcribe in eukaryotes

Area of Science:

• Molecular Biology
• Epigenetics
• Genomics

Background:

• Nucleosomes act as barriers to RNA Polymerase II (Pol II) during gene transcription in eukaryotes.
• The +1 nucleosome upstream of transcription start sites can cause Pol II pausing.
• Fragile nucleosome structures, like tailless nucleosomes, have been implicated in resolving Pol II pausing.

Purpose of the Study:

• To investigate the role of histone modifications, specifically pan-acetylation and pan-phosphorylation, in creating fragile nucleosomes.
• To determine if these fragile nucleosomes are essential for resolving nucleosome resistance to Pol II elongation.
• To systematically analyze histone modifications across the human genome in relation to Pol II activity.

Main Methods:

• Systematic analysis of pan-acetylation and pan-phosphorylation of histones genome-wide.
• Utilized HEK293T cells for cellular experiments.
• Correlated histone modification patterns with RNA Polymerase II activity along gene bodies.

Main Results:

• Both histone pan-acetylation and pan-phosphorylation in nucleosomes are coupled with Pol II activity along gene bodies.
• Identified four major types of fragile nucleosomes crucial for Pol II transcription.
• These fragile nucleosomes include tailless, predominantly acetylated, predominantly phosphorylated, and dual-modified forms.

Conclusions:

• Fragile nucleosomes are essential for efficient Pol II transcription through gene bodies.
• Histone acetylation and phosphorylation play key roles in generating these transcription-permissive nucleosome structures.
• The findings reveal a novel mechanism involving diverse fragile nucleosome types that facilitate gene transcription.