Journal: Nature / Year: 2018 Title: Prespliceosome structure provides insights into spliceosome assembly and regulation. Authors: Clemens Plaschka / Pei-Chun Lin / Clément Charenton / Kiyoshi Nagai / Abstract: The spliceosome catalyses the excision of introns from pre-mRNA in two steps, branching and exon ligation, and is assembled from five small nuclear ribonucleoprotein particles (snRNPs; U1, U2, U4, ...The spliceosome catalyses the excision of introns from pre-mRNA in two steps, branching and exon ligation, and is assembled from five small nuclear ribonucleoprotein particles (snRNPs; U1, U2, U4, U5, U6) and numerous non-snRNP factors. For branching, the intron 5' splice site and the branch point sequence are selected and brought by the U1 and U2 snRNPs into the prespliceosome, which is a focal point for regulation by alternative splicing factors. The U4/U6.U5 tri-snRNP subsequently joins the prespliceosome to form the complete pre-catalytic spliceosome. Recent studies have revealed the structural basis of the branching and exon-ligation reactions, however, the structural basis of the early events in spliceosome assembly remains poorly understood. Here we report the cryo-electron microscopy structure of the yeast Saccharomyces cerevisiae prespliceosome at near-atomic resolution. The structure reveals an induced stabilization of the 5' splice site in the U1 snRNP, and provides structural insights into the functions of the human alternative splicing factors LUC7-like (yeast Luc7) and TIA-1 (yeast Nam8), both of which have been linked to human disease. In the prespliceosome, the U1 snRNP associates with the U2 snRNP through a stable contact with the U2 3' domain and a transient yeast-specific contact with the U2 SF3b-containing 5' region, leaving its tri-snRNP-binding interface fully exposed. The results suggest mechanisms for 5' splice site transfer to the U6 ACAGAGA region within the assembled spliceosome and for its subsequent conversion to the activation-competent B-complex spliceosome. Taken together, the data provide a working model to investigate the early steps of spliceosome assembly.
History
Deposition
Apr 10, 2018
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Header (metadata) release
May 16, 2018
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Map release
Jul 18, 2018
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Update
Nov 25, 2020
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Current status
Nov 25, 2020
Processing site: PDBe / Status: Released
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Structure visualization
Movie
Surface view with section colored by density value
Model: Quantifoil R2/2 / Material: COPPER / Mesh: 400 / Support film - Material: CARBON / Support film - topology: HOLEY / Pretreatment - Type: GLOW DISCHARGE
Vitrification
Cryogen name: ETHANE / Chamber humidity: 100 % / Instrument: FEI VITROBOT MARK III Details: Grids were blotted for 2-3.5 s and vitrified by plunging into liquid ethane with a FEI Vitrobot Mark III operated at 4 degree Celsius and 100% humidity..
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Electron microscopy
Microscope
FEI TITAN KRIOS
Image recording
Film or detector model: GATAN K2 SUMMIT (4k x 4k) / Detector mode: COUNTING / Number real images: 9407 / Average electron dose: 43.0 e/Å2
Electron beam
Acceleration voltage: 300 kV / Electron source: FIELD EMISSION GUN
Electron optics
Illumination mode: FLOOD BEAM / Imaging mode: BRIGHT FIELD / Cs: 2.7 mm / Nominal magnification: 105000
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