An acetylation-mediated chromatin switch governs H3K4 methylation read-write capability.

Area of Science:

• Epigenetics
• Molecular Biology
• Chromatin Biology

Background:

• Histone N-terminal tails in nucleosomes dynamically shift between accessible and DNA-bound states.
• Histone tail accessibility influences epigenetic machinery interactions.
• H3 tail acetylation (e.g., K9ac, K14ac, K18ac) is known to enhance H3K4me3 reader engagement.

Purpose of the Study:

• To investigate if H3 tail acetylation broadly impacts H3K4 methylation readers and writers.
• To determine if this acetylation-mediated regulation extends beyond known reader interactions.
• To elucidate the mechanism linking H3 tail acetylation and H3K4 methylation levels.

Main Methods:

• Utilized fully-defined heterotypic nucleosomes to study histone tail regulation.
• Assessed nucleosomal accessibility to H3K4 methyl readers and writers.
• Performed in vivo studies to correlate H3 tail acetylation with H3K4 methylation dynamics.

Main Results:

• H3 tail acetylation enhances nucleosomal accessibility for additional H3K4 methyl readers.
• Acetylation also promotes accessibility for H3K4 methyl writers, including MLL1.
• This regulatory effect is specific to the nucleosome context (cis H3 tail) and not observed on peptides.
• In vivo, H3 tail acetylation is dynamically coupled with cis H3K4 methylation.

Conclusions:

• H3 tail acetylation functions as a 'chromatin switch', modulating nucleosome accessibility.
• This switch controls the engagement of both H3K4 methylation readers and writers.
• The findings resolve the question of why H3K4me3 levels are coupled with H3 acetylation.