In:
Nature, Springer Science and Business Media LLC, Vol. 596, No. 7871 ( 2021-08-12), p. 296-300
Abstract:
During the splicing of introns from precursor messenger RNAs (pre-mRNAs), the U2 small nuclear ribonucleoprotein (snRNP) must undergo stable integration into the spliceosomal A complex—a poorly understood, multistep process that is facilitated by the DEAD-box helicase Prp5 (refs. 1–4 ). During this process, the U2 small nuclear RNA (snRNA) forms an RNA duplex with the pre-mRNA branch site (the U2–BS helix), which is proofread by Prp5 at this stage through an unclear mechanism 5 . Here, by deleting the branch-site adenosine (BS-A) or mutating the branch-site sequence of an actin pre-mRNA, we stall the assembly of spliceosomes in extracts from the yeast Saccharomyces cerevisiae directly before the A complex is formed. We then determine the three-dimensional structure of this newly identified assembly intermediate by cryo-electron microscopy. Our structure indicates that the U2–BS helix has formed in this pre-A complex, but is not yet clamped by the HEAT domain of the Hsh155 protein (Hsh155 HEAT ), which exhibits an open conformation. The structure further reveals a large-scale remodelling/repositioning of the U1 and U2 snRNPs during the formation of the A complex that is required to allow subsequent binding of the U4/U6.U5 tri-snRNP, but that this repositioning is blocked in the pre-A complex by the presence of Prp5. Our data suggest that binding of Hsh155 HEAT to the bulged BS-A of the U2–BS helix triggers closure of Hsh155 HEAT , which in turn destabilizes Prp5 binding. Thus, Prp5 proofreads the branch site indirectly, hindering spliceosome assembly if branch-site mutations prevent the remodelling of Hsh155 HEAT . Our data provide structural insights into how a spliceosomal helicase enhances the fidelity of pre-mRNA splicing.
Type of Medium:
Online Resource
ISSN:
0028-0836
,
1476-4687
DOI:
10.1038/s41586-021-03789-5
Language:
English
Publisher:
Springer Science and Business Media LLC
Publication Date:
2021
detail.hit.zdb_id:
120714-3
detail.hit.zdb_id:
1413423-8
SSG:
11
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