Download MendeleyStructural insights into how Prp5 proofreads the pre-mRNA branch site.
Zhang, Z., Rigo, N., Dybkov, O., Fourmann, J.B., Will, C.L., Kumar, V., Urlaub, H., Stark, H., Luhrmann, R.(2021) Nature 596: 296-300
- PubMed: 34349264
- DOI: https://doi.org/10.1038/s41586-021-03789-5
- Primary Citation of Related Structures:
7OQB, 7OQC, 7OQE - PubMed 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.
Organizational Affiliation:
Department of Structural Dynamics, MPI for Biophysical Chemistry, Göttingen, Germany.
