Pre-mRNA splicing requires the assembly, remodeling, and disassembly of the multi-megadalton ribonucleoprotein complex called the spliceosome¹. Recent studies have shed light on spliceosome assembly and remodeling for catalysis^2–6, but the mechanism of disassembly remains unclear. Here, we report 2.6 to 3.2 Å resolution cryo-electron microscopy structures of nematode and human terminal intron-lariat spliceosomes along with biochemical and genetic data. Our results uncover how four disassembly factors and the conserved RNA helicase DHX15 initiate spliceosome disassembly. The disassembly factors probe large inner and outer spliceosome surfaces to detect the release of ligated mRNA. Two of these factors, TFIP11 and C19L1, and three general spliceosome subunits, SYF1, SYF2 and SDE2, then dock and activate DHX15 on the catalytic U6 snRNA to initiate disassembly. U6 thus controls both the start⁵ and end of pre-mRNA splicing. Taken together, our results explain the molecular basis of canonical spliceosome disassembly and provide a framework to understand general spliceosomal RNA helicase control and the discard of aberrant spliceosomes.

前 mRNA 剪接需要被称为剪接体 ¹ 的多兆道尔顿核糖核蛋白复合物的组装、重塑和分解。最近的研究揭示了催化作用的剪接体组装和重塑 ^2–6 ，但分解机制仍不清楚。在这里，我们报告了线虫和人类末端内含子套索剪接体的 2.6 至 3.2 Å 分辨率冷冻电子显微镜结构以及生化和遗传数据。我们的结果揭示了四种分解因子和保守的 RNA 解旋酶 DHX15 如何启动剪接体分解。拆卸因子探测大的内剪接体和外剪接体表面以检测连接的 mRNA 的释放。其中两个因子 TFIP11 和 C19L1，以及三个通用剪接体亚基 SYF1、SYF2 和 SDE2，然后对接并激活催化 U6 snRNA 上的 DHX15 以启动分解。因此，U6 控制前 mRNA 剪接的起始 ⁵ 和结束。总而言之，我们的结果解释了典型剪接体分解的分子基础，并提供了一个框架来理解一般剪接体 RNA 解旋酶控制和异常剪接体的丢弃。