FACT frees Ubp10 from nucleosome sequestration after rapid H2B deubiquitination

FACT relieves a release bottleneck for the yeast deubiquitinase Ubp10 on individual H2B-ubiquitinated nucleosomes, enabling faster Ubp10 dissociation.

• Why it matters: Enzymes must bind, act, and release substrates on chromatin, but it was unclear whether catalysis or release limits turnover for Ubp10.
• What they did: Using three-color single-molecule fluorescence, Ubp10 cleaved ubiquitin from H2B within seconds of binding yet stayed bound to ~80% of nucleosomes after 45 minutes; FACT accelerated Ubp10-nucleosome dissociation.
• The result: In living yeast, depleting FACT via nuclear loss of Spt16 increased the slowly diffusing, chromatin-bound Ubp10 fraction, supporting FACT-dependent release as a recycling mechanism.

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