253: Nap1 and histone acetylation tune chromatin condensates

Gao J et al., Nature Communications - H4 tail lysine residues drive liquid-liquid phase separation of 12‑mer nucleosome arrays, while H3 tail acetylation and the histone chaperone Nap1 increase internal dynamics and lower droplet viscosity. Key terms: Nap1, H3 acetylation, H4 acetylation, liquid-liquid phase separation, nucleosome arrays. Study Highlights:H4 tail lysine residues are the primary drivers of nucleosome array phase separation, and H4-tail acetylation prevents droplet formation. H3 tail acetylation mimic (H3KQ) and in situ H3 acetylation speed fluorescence recovery, indicating enhanced DNA–histone dynamics. Nap1 dissolves gel-like aggregates formed by tailless H3 arrays, increases nucleosome concentration inside droplets from ~326 µM to ~491 µM, and accelerates internal dynamics. STORM imaging reveals condensed droplets contain both a mobile fraction and a relatively immobile structural scaffold. Optical-tweezers microrheology identifies two relaxation components and shows Nap1 and H3KQ specifically lower the relaxation time and viscosity of the slower scaffold-associated component Conclusion:Histone H4 tail lysines govern chromatin phase separation while H3 acetylation and Nap1 tune the fluidity and accessibility of condensed chromatin Music:Enjoy the music based on this article at the end of the episode. Article title:Roles of histone chaperone Nap1 and histone acetylation in regulating phase-separation of nucleosome arrays First author:Gao J Journal:Nature Communications DOI:10.1038/s41467-025-65701-3 Reference:Gao J, Li H, Tan S, Zhou R & Lee T-H. Roles of histone chaperone Nap1 and histone acetylation in regulating phase-separation of nucleosome arrays. Nature Communications. 2025;16:10672. https://doi.org/10.1038/s41467-025-65701-3 License:This episode is based on an open-access article published under the Creative Commons Attribution 4.0 International License (CC BY 4.0) – https://creativecommons.org/licenses/by/4.0/ Support:Base by Base – Stripe donations: https://donate.stripe.com/7sY4gz71B2sN3RWac5gEg00 Official website https://basebybase.com On PaperCast Base by Base you’ll discover the latest in genomics, functional genomics, structural genomics, and proteomics. Episode link: https://basebybase.com/episodes/nap1-histone-acetylation QC:This episode was checked against the original article PDF and publication metadata for the episode release published on 2026-01-08. QC Scope:- article metadata and core scientific claims from the narration- excludes analogies, intro/outro, and music- transcript coverage: Substantively audited sections cover the core biophysical mechanisms and measurements: LLPS initiation by H4 tail, effects of H4KQ and H3KQ on droplet formation and dynamics, Nap1’s dual role, FRAP, STORM, microrheology with two relaxation components, and H2A–H2B exchange context.- transcript topics: LLPS of nucleosome arrays driven by H4 tail lysines; H4KQ acetylation mimic blocks droplet formation; H3 tail acetylation mimic (H3KQ) increases dynamics but does not block LLPS; Nap1 dissolves aggregates and increases nucleosome concentration inside condensates; STORM reveals mobile fraction and immobile scaffold inside droplets; Microrheology with optical traps identifying two relaxation components QC Summary:- factual score: 10/10- metadata score: 10/10- supported core claims: 8- claims flagged for review: 0- metadata checks passed: 4- metadata issues found: 0 Metadata Audited:- article_doi- article_title- article_journal- license Factual Items Audited:- H4 tail lysine residues drive LLPS of nucleosome arrays- H4KQ acetylation mimic blocks droplet formation- H3KQ acetylation mimic increases dynamic...