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 Cryo–electron microscopy structures of the postcatalytic spliceosome elucidate mechanisms of RNA splicing. Introns are removed from eukaryotic messenger RNA precursors by the spliceosome in two transesterification reactions—branching and exon ligation. The mechanism of 3′–splice site recognition during exon ligation has remained unclear. Here we present the 3.7-angstrom cryo–electron microscopy structure of the yeast P-complex spliceosome immediately after exon ligation. The 3′–splice site AG dinucleotide is recognized through non–Watson-Crick pairing with the 5′ splice site and the branch-point adenosine. After the branching reaction, protein factors work together to remodel the spliceosome and stabilize a conformation competent for 3′–splice site docking, thereby promoting exon ligation. The structure accounts for the strict conservation of the GU and AG dinucleotides at the 5′ and 3′ ends of introns and provides insight into the catalytic mechanism of exon ligation.

中文翻译：

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催化后剪接体结构揭示了 3'-剪接位点选择的机制

了解 3' 端的剪接 剪接体从真核 mRNA 前体中去除内含子，并通过连接外显子产生成熟的转录本。尽管在理解剪接体结构方面进行了数十年的功能研究和最近的进展，但剪接体识别 3' 剪接位点 (SS) 的机制仍不清楚。刘等人。和威尔金森等人。报告酵母后催化剪接体的高分辨率低温电子显微镜结构。结构表明，3'SS 是通过与 5'SS 和分支点的非 Watson-Crick 碱基配对识别的，由内含子区域和蛋白质因子稳定。科学，本期第 3 页。第 1278 页，第 1283 催化后剪接体的冷冻电子显微镜结构阐明了 RNA 剪接的机制。通过剪接体在两个酯交换反应（分支和外显子连接）中从真核信使 RNA 前体中去除内含子。外显子连接过程中 3'-剪接位点识别的机制仍不清楚。在这里，我们在外显子连接后立即展示了酵母 P-复合体剪接体的 3.7 埃低温电子显微镜结构。3'-剪接位点 AG 二核苷酸通过与 5' 剪接位点和分支点腺苷的非 Watson-Crick 配对来识别。在分支反应之后，蛋白质因子共同作用以重塑剪接体并稳定能够进行3'-剪接位点对接的构象，从而促进外显子连接。