Linker histone H1 represses H3 tail acetylation induced by H4 tail acetylation and alters its dynamics

The nucleosome is the fundamental chromatin unit, containing two copies of histones H2A, H2B, H3, and H4 wrapped by ~ 146 bp of core DNA plus linker DNA; addition of linker histone H1 forms a chromatosome. Tetra-acetylation of the H4 N-terminal tail (H4-4Kac) enhances H3 N-tail acetylation by altering their mutual dynamics, but how H1 influences these dynamics remains unclear. Using cryo-electron microscopy and coarse-grained molecular dynamics simulations, we show that H4-4Kac and unmodified chromatosomes share essentially identical core histone-DNA structures and similar H3 N-tail dynamics. However, nuclear magnetic resonance spectroscopy reveals that in the H4-4Kac chromatosome, the H3 N-tail adopts a dynamically robust DNA-contact state distinct from that in the unmodified chromatosome, resulting in markedly reduced H3 N-tail acetylation. These findings suggest that linker histone H1 suppresses the progression of euchromatin formation.