Journal: Mol Cell / Year: 2026 Title: The +1 nucleosome functions in RNA Pol II transcription initiation and the transition to elongation. Authors: Yumeng Zhan / Julio Abril-Garrido / Frauke Grabbe / Paulina Seweryn / Ute Neef / Christian Dienemann / Patrick Cramer / Abstract: Transcription initiation by RNA polymerase II (RNA Pol II) occurs next to a +1 nucleosome, which is positioned downstream of the transcription start site (TSS). The +1 nucleosome influences pre- ...Transcription initiation by RNA polymerase II (RNA Pol II) occurs next to a +1 nucleosome, which is positioned downstream of the transcription start site (TSS). The +1 nucleosome influences pre-initiation complex (PIC) assembly and RNA Pol II pausing, but its function in transcription initiation and the transition to elongation remains unclear. Here, we investigate the transcription initiation-elongation transition in vitro using DNA templates containing a +1 nucleosome and present cryo-electron microscopy (cryo-EM) structures of five intermediate states. First, after PIC assembly, ATP binding to TFIIH enables the +1 nucleosome to evict TFIID from the PIC. Following DNA opening, the +1 nucleosome stimulates TFIIH translocase activity and initial RNA synthesis. Finally, after DNA bubble rewinding, the +1 nucleosome removes TFIIH from the early elongation complex for promoter escape. Our findings show that the +1 nucleosome not only acts passively in PIC assembly and RNA Pol II pausing but rather has active functions during the initiation-elongation transition of transcription.
Macromolecule #1: General transcription and DNA repair factor IIH helicase subunit XPB
Macromolecule
Name: General transcription and DNA repair factor IIH helicase subunit XPB type: protein_or_peptide / ID: 1 / Number of copies: 1 / Enantiomer: LEVO / EC number: DNA helicase
Name: ZINC ION / type: ligand / ID: 37 / Number of copies: 17 / Formula: ZN
Molecular weight
Theoretical: 65.409 Da
+
Macromolecule #38: MAGNESIUM ION
Macromolecule
Name: MAGNESIUM ION / type: ligand / ID: 38 / Number of copies: 1 / Formula: MG
Molecular weight
Theoretical: 24.305 Da
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Experimental details
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Structure determination
Method
cryo EM
Processing
single particle reconstruction
Aggregation state
particle
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Sample preparation
Buffer
pH: 7.5
Grid
Model: Quantifoil R3.5/1 / Material: COPPER / Mesh: 200 / Support film - Material: CARBON / Support film - topology: CONTINUOUS / Support film - Film thickness: 3
Vitrification
Cryogen name: ETHANE / Chamber humidity: 100 % / Chamber temperature: 277 K / Instrument: FEI VITROBOT MARK IV
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Electron microscopy
Microscope
TFS KRIOS
Specialist optics
Energy filter - Name: GIF Quantum SE / Energy filter - Slit width: 20 eV
Image recording
Film or detector model: GATAN K3 (6k x 4k) / Number real images: 79440 / Average exposure time: 3.0 sec. / Average electron dose: 40.0 e/Å2
Electron beam
Acceleration voltage: 300 kV / Electron source: FIELD EMISSION GUN
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