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. 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.

中文翻译：

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酵母剪接体后催化 P 复合物的结构


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。尽管进行了数十年的功能研究并且最近在理解剪接体结构方面取得了进展，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。报告了酵母后催化剪接体的高分辨率冷冻电子显微镜结构。该结构表明，3'SS 通过与 5'SS 和分支点的非沃森-克里克碱基配对来识别，并由内含子区域和蛋白质因子稳定。科学，本期第 14 页。 1278，p。第1283章 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。剪接体在剪接周期中经历巨大的变化。 B、Bact、C、C* 和内含子套索剪接体复合物的结构揭示了 5'-剪接位点 (ss) 识别、分支和内含子释放的机制，但缺乏有关 3'-ss 识别、外显子连接和外显子的信息发布。在这里，我们以 3.3 埃分辨率报道了催化后 P 配合物的冷冻电子显微镜结构，揭示了 3' SS 主要通过与 5' SS 和分支点的非沃森-克里克碱基配对来识别。此外，一种或多种未鉴定的蛋白质与 P 复合物稳定结合，保护 3' 外显子并可能调节解旋酶 Prp22 的活性。 Prp22 结合 3' 外显子中的 15 至 21 号核苷酸，使其能够沿 3' 至 5' 方向拉动内含子-外显子或连接的外显子，从而分别实现 3'-ss 校对或外显子释放。