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Structural basis for the synergistic assembly of the snRNA export complex
Etienne Dubiez1,2, William Garland3, Maja Finderup Brask3
1Université Grenoble Alpes, CNRS, CEA, IBS, Grenoble, France.
Nature Structural & Molecular Biology
|July 3, 2025
Summary
The nuclear cap-binding complex (CBC) and PHAX protein form a crucial snRNA export complex. This structure reveals how PHAX bridges CBC to export factors, displacing ARS2 and committing the complex for nuclear export.
Area of Science:
- Molecular Biology
- Structural Biology
- RNA Biology
Background:
- The nuclear cap-binding complex (CBC) and ARS2 regulate RNA polymerase II transcripts.
- PHAX is an effector that mediates the nuclear export of U-rich small nuclear RNAs (snRNAs).
Purpose of the Study:
- To elucidate the structural mechanism of the human snRNA export complex.
- To understand the role of PHAX, CBC, CRM1-RanGTP, and capped RNA in snRNA nuclear export.
Main Methods:
- Cryo-electron microscopy (cryo-EM) to determine the structure of the snRNA export complex.
- Biochemical assays to investigate protein-protein and protein-RNA interactions.
Main Results:
- The cryo-EM structure reveals PHAX bridging CBC to CRM1-RanGTP, reinforcing cap binding.
- PHAX's phosphorylated region interacts with RanGTP, and CBC binding is incompatible with other effectors like ALYREF or NCBP3.
- snRNA export complex formation requires synergistic binding, displacing ARS2 from CBC.
Conclusions:
- The synergistic assembly of the snRNA export complex commits it for nuclear export.
- This structural insight clarifies the regulation of snRNA export by CBC, PHAX, and CRM1-RanGTP.
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