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Researchers used single-molecule fluorescence microscopy to observe the yeast enzyme Ubp10 removing ubiquitin marks from histone H2B on individual nucleosomes. They discovered that while Ubp10 performs the removal reaction within seconds, it remains stuck to the nucleosome for extended periods afterward, with approximately 80% still bound after 45 minutes. The histone chaperone protein FACT resolves this problem by accelerating the release of Ubp10 from nucleosomes, allowing the enzyme to be recycled and act on additional targets.
Why it matters
This work reveals that enzyme release, rather than the catalytic reaction itself, can be the rate-limiting step in chromatin modification, providing a new regulatory mechanism for gene expression control. The findings suggest that chaperone proteins like FACT play crucial roles in maintaining efficient enzyme turnover on chromatin, which could inform therapeutic strategies targeting epigenetic modifications.
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⚠️ Preprint – Noch nicht peer-reviewed
Dieser Artikel wurde noch nicht von unabhängigen Experten begutachtet. Die Ergebnisse sind vorläufig und sollten mit Vorsicht interpretiert werden.
Chromatin-modifying enzymes must engage their substrate, act on it and release it, but which step limits their turnover is unclear. Using three-color single-molecule fluorescence, we directly visualized the yeast deubiquitinase Ubp10 removing ubiquitin from H2B on individual nucleosomes. Ubp10 cleaved the mark within seconds of binding, without detectable DNA unwrapping, yet it did not let go: ~80% of nucleosomes remained bound after 45 minutes, and unmodified nucleosomes formed similarly long-lived complexes. Ubp10 turnover is therefore limited by release rather than catalysis. The histone chaperone FACT relieved this bottleneck by accelerating Ubp10-nucleosome dissociation. In living yeast, nuclear depletion of the FACT subunit Spt16 increased the slowly diffusing, chromatin-bound fraction of nucleoplasmic Ubp10. These findings identify FACT-dependent release as a likely mechanism for recycling Ubp10 on chromatin. More broadly, a nucleosome can sequester the enzyme acting on it, making enzyme release a step at which chromatin modification can be controlled.
Source: FACT frees Ubp10 from nucleosome sequestration after rapid H2B deubiquitination