研究人员表明，逆转录转座是由结构复杂的核糖酶、其蛋白移动因子和结构化的DNA底物之间的三级复合物实现的。研究人员解析了一个完整的IIC组内切酶逆转录元件的冷冻电镜结构，该元件准备整合到一个DNA茎环模体中。通过对DNA靶向前后的核糖核蛋白（RNP）进行可视化，研究人员表明它已经做好了攻击的准备，并与它的DNA靶点完全吻合。
这项研究揭示了原型逆转录元件的设计原则，并加强了第II组内含子是遗传多样化古老元件的假设。
第II组内含子是核糖核酸酶，能够催化其自我切除，并作为侵入DNA的逆转录元件发挥作用。作为逆转录元件，第二组内含子形成核糖核蛋白（RNP）复合物，在基因组中游荡，通过逆转正向剪接进行整合。
附：英文原文
Title: Structures of a mobile intron retroelement poised to attack its structured DNA target
Author: Kevin Chung, Ling Xu, Pengxin Chai, Junhui Peng, Swapnil C. Devarkar, Anna Marie Pyle
Issue&Volume: 2022-11-11
Abstract: Group II introns are ribozymes that catalyze their self-excision and function as retroelements that invade DNA. As retrotransposons, group II introns form ribonucleoprotein (RNP) complexes that roam the genome, integrating by reversal of forward splicing. Here we show that retrotransposition is achieved by a tertiary complex between a structurally elaborate ribozyme, its protein mobility factor, and a structured DNA substrate. We solved cryo–electron microscopy structures of an intact group IIC intron-maturase retroelement that was poised for integration into a DNA stem-loop motif. By visualizing the RNP before and after DNA targeting, we show that it is primed for attack and fits perfectly with its DNA target. This study reveals design principles of a prototypical retroelement and reinforces the hypothesis that group II introns are ancient elements of genetic diversification.
DOI: abq2844
Source: https://www.science.org/doi/10.1126/science.abq2844