Research Article

Structure of the yeast spliceosomal postcatalytic P complex

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Science  08 Dec 2017:
Vol. 358, Issue 6368, pp. 1278-1283
DOI: 10.1126/science.aar3462

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Understanding splicing from the 3′ end

The spliceosome removes introns from eukaryotic mRNA precursors and yields mature transcripts by joining exons. Despite decades of functional studies and recent progress in understanding the spliceosome structure, the mechanism by which the 3′ splice site (SS) is recognized by the spliceosome has remained unclear. Liu et al. and Wilkinson et al. report the high-resolution cryo-electron microscopy structures of the yeast postcatalytic spliceosome. The structures reveal that the 3′SS is recognized through non-Watson-Crick base pairing with the 5′SS and the branch point, stabilized by the intron region and protein factors.

Science, this issue p. 1278, p. 1283


The spliceosome undergoes dramatic changes in a splicing cycle. Structures of B, Bact, C, C*, and intron lariat spliceosome complexes revealed mechanisms of 5′–splice site (ss) recognition, branching, and intron release, but lacked information on 3′-ss recognition, exon ligation, and exon release. Here we report a cryo–electron microscopy structure of the postcatalytic P complex at 3.3-angstrom resolution, revealing that the 3′ ss is mainly recognized through non–Watson-Crick base pairing with the 5′ ss and branch point. Furthermore, one or more unidentified proteins become stably associated with the P complex, securing the 3′ exon and potentially regulating activity of the helicase Prp22. Prp22 binds nucleotides 15 to 21 in the 3′ exon, enabling it to pull the intron-exon or ligated exons in a 3′ to 5′ direction to achieve 3′-ss proofreading or exon release, respectively.

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