A unified model for intron definition, exon definition, and back-splicing

In vitro assembly and purification of the ACT1 complex

Secondary structures in the region between the 5′ SS and BPS in the wild-type and mutant ACT1 and UBC4 pre-mRNAs

Protein interactions in the UBC4 complex

Computational, biochemical, and structural characterization of the EDC

Characterization of circRNAs.

研究报道了在内含子上组装的酵母剪接体E复合物的冷冻电镜结构，提供了剪接周期（确定mRNA前体进行剪接）中最早事件的视图。E复合物结构表明相同的剪接体可以跨越外显子组装，并且它要么重构以跨越内含子用于规范的线性剪接（通常在短外显子上），要么催化反向剪接以产生环状RNA（在长外显子上）。该模型得到了实验的支持，即当外显子足够长时，在酵母EFM5或HMRA1基因的中间外显子上组装的E复合物可形成环状RNA。这个简单的模型统一了真核生物中利用相同剪接体的内含子定义、外显子定义和反向剪接，并且能够促进许多其他系统中的研究来理解这些过程的机制和调控。

研究表示，外显子定义和反向剪接的分子机制是mRNA前体剪接中尚未解决的基本问题。

附：

Title: A unified mechanism for intron and exon definition and back-splicing

Author: Xueni Li, Shiheng Liu, Lingdi Zhang, Aaron Issaian, Ryan C. Hill, Sara Espinosa, Shasha Shi, Yanxiang Cui, Kalli Kappel, Rhiju Das, Kirk C. Hansen, Z. Hong Zhou, Rui Zhao

Issue&Volume: 2019-09-04

Abstract: The molecular mechanisms of exon definition and back-splicing are fundamental unanswered questions in pre-mRNA splicing. Here we report cryo-electron microscopy structures of the yeast spliceosomal E complex assembled on introns, providing a view of the earliest event in the splicing cycle that commits pre-mRNAs to splicing. The E complex architecture suggests that the same spliceosome can assemble across an exon, and that it either remodels to span an intron for canonical linear splicing (typically on short exons) or catalyses back-splicing to generate circular RNA (on long exons). The model is supported by our experiments, which show that an E complex assembled on the middle exon of yeast EFM5 or HMRA1 can be chased into circular RNA when the exon is sufficiently long. This simple model unifies intron definition, exon definition, and back-splicing through the same spliceosome in all eukaryotes and should inspire experiments in many other systems to understand the mechanism and regulation of these processes.

DOI: 10.1038/s41586-019-1523-6

Source:https://www.nature.com/articles/s41586-019-1523-6