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Updated: Feb 2, 2026

Making Precise and Accurate Single-Molecule FRET Measurements using the Open-Source smfBox
Published on: July 5, 2021
High precision FRET studies reveal reversible transitions in nucleosomes between microseconds and minutes
Alexander Gansen1, Suren Felekyan2, Ralf Kühnemuth2
1DKFZ, Div. Biophysics of Macromolecules, 69120, Heidelberg, Germany.
Abstract:
Nucleosomes play a dual role in compacting the genome and regulating the access to DNA. To unravel the underlying mechanism, we study fluorescently labeled mononucleosomes by multi-parameter FRET measurements and characterize their structural and dynamic heterogeneity upon NaCl-induced destabilization. Species-selective fluorescence lifetime analysis and dynamic photon distribution analysis reveal intermediates during nucleosome opening and lead to a coherent structural and kinetic model. In dynamic octasomes and hexasomes the interface between the H2A-H2B dimers and the (H3-H4)2 tetramer opens asymmetrically by an angle of ≈20° on a 50 and 15 µs time scale, respectively. This is followed by a slower stepwise release of the dimers coupled with DNA unwrapping. A mutation (H2A-R81A) at the interface between H2A and H3 facilitates initial opening, confirming the central role of the dimer:tetramer interface for nucleosome stability. Partially opened states such as those described here might serve as convenient nucleation sites for DNA-recognizing proteins.
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