Nucleosome Dynamics during Transcription Elongation

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Nucleosomes are fundamental eukaryotic genome packing units.
• DNA-histone interactions regulate gene accessibility and DNA-templated processes like transcription.
• RNA Polymerase II (Pol II) elongation is a key DNA-templated process influenced by nucleosome dynamics.

Purpose of the Study:

• Investigate nucleosome dynamics during transcription elongation.
• Determine the effects of H3 K56 acetylation and histone chaperone Nap1 on Pol II progression.
• Understand how these factors influence DNA-histone interactions and nucleosome integrity.

Main Methods:

• Single-molecule Förster Resonance Energy Transfer (smFRET) measurements.
• Utilized chemically modified histones to study nucleosome dynamics.
• Observed Pol II transcription through reconstituted nucleosomes.

Main Results:

• H3 K56 acetylation significantly reduced Pol II pause duration near the nucleosome entry.
• Nap1 did not notably alter Pol II pausing or elongation rates.
• Elongation rate of Pol II through the nucleosome remained unaffected by acetylation or Nap1.
• A small fraction of intact nucleosomes remained post-transcription, irrespective of H3 K56 acetylation or Nap1.

Conclusions:

• H3 K56 acetylation facilitates Pol II translocation by aiding paused Pol II to resume.
• Nap1 does not influence Pol II progression through nucleosomes.
• Spontaneous nucleosome opening likely enables Pol II progression.
• Pol II is inefficient at mediating nucleosome reassembly post-transcription.
• Nap1 alone does not promote nucleosome disassembly or reassembly during transcription.