National Institutes of Health/National Institute of General Medical Sciences (NIH/NIGMS)
R35 GM118130
United States
Life Sciences Research Foundation
Agouron Institute
United States
Citation
Journal: Nat Commun / Year: 2025 Title: Real-time capture of σ transcription initiation intermediates reveals mechanism of ATPase-driven activation by limited unfolding. Authors: Andreas U Mueller / Nina Molina / B Tracy Nixon / Seth A Darst / Abstract: Bacterial σ factors bind RNA polymerase (E) to form holoenzyme (Eσ), conferring promoter specificity to E and playing a key role in transcription bubble formation. σ is unique among σ factors in ...Bacterial σ factors bind RNA polymerase (E) to form holoenzyme (Eσ), conferring promoter specificity to E and playing a key role in transcription bubble formation. σ is unique among σ factors in its structure and functional mechanism, requiring activation by specialized AAA+ ATPases. Eσ forms an inactive promoter complex where the N-terminal σ region I (σ-RI) threads through a small DNA bubble. On the opposite side of the DNA, the ATPase engages σ-RI within the pore of its hexameric ring. Here, we perform kinetics-guided structural analysis of de novo formed Eσ initiation complexes and engineer a biochemical assay to measure ATPase-mediated σ-RI translocation during promoter melting. We show that the ATPase exerts mechanical action to translocate about 30 residues of σ-RI through the DNA bubble, disrupting inhibitory structures of σ to allow full transcription bubble formation. A local charge switch of σ-RI from positive to negative may help facilitate disengagement of the otherwise processive ATPase, allowing subsequent σ disentanglement from the DNA bubble.
pH: 8 Details: 40 mM Tris-HCl, pH 8/RT, 200 mM KCl, 10 mM MgCl2, 1 mM DTT; fluorinated fos-choline-8 (FC8F) added to a final concentration of 1.5 mM during grid preparation
Grid
Model: C-flat-1.2/1.3 / Material: GOLD / Mesh: 400 / Support film - Material: CARBON / Support film - topology: HOLEY / Pretreatment - Type: GLOW DISCHARGE / Pretreatment - Time: 5 sec. / Pretreatment - Atmosphere: AIR / Pretreatment - Pressure: 0.03 kPa / Details: 25 mA
Vitrification
Cryogen name: ETHANE / Chamber humidity: 100 % / Chamber temperature: 310 K / Instrument: FEI VITROBOT MARK IV
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Electron microscopy
Microscope
TFS KRIOS
Image recording
Film or detector model: GATAN K3 BIOQUANTUM (6k x 4k) / Digitization - Dimensions - Width: 11520 pixel / Digitization - Dimensions - Height: 8184 pixel / Number grids imaged: 1 / Number real images: 17199 / Average exposure time: 1.4 sec. / Average electron dose: 42.0 e/Å2
Electron beam
Acceleration voltage: 300 kV / Electron source: FIELD EMISSION GUN
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