美国加州大学Navtej Toor研究组观察到了II族内含子反向剪接DNA的冷冻电镜结构。2019年7月25日出版的《细胞》杂志发表了这一最新研究成果。

研究小组以3.6埃的分辨率确定了Ⅱ族内含子反向剪接到DNA的两组冷冻电镜结构。这些结构揭示了分支-位点域VI螺旋旋转90°，使DNA整合过程中能狗进行底物交换。成熟酶通过与域VI的短暂RNA蛋白接触来辅助催化，该域在正向剪接过程中为套索的形成定位分枝位点腺苷。这些发现为成熟酶在Ⅱ族内含子催化中的作用提供了第一个直接证据。域VI动力学与剪接体分支-位点螺旋运动密切平行，为剪接体的后向起源提供了强有力的证据。

据介绍，第二组内含子是一类逆转录因子，通过一种称为逆转录转座的复制粘贴机制侵入DNA。它们的协同活动发生在包含成熟酶蛋白的复合物中，成熟酶蛋白通过未知的机制促进剪接。在催化过程中RNA活性位点内剪接位点交换的机制也尚不清楚。

附：英文原文

Title: Cryo-EM Structures of a Group II =Intron Reverse Splicing into DNA

Author: Daniel B. Haack, Xiaodong Yan, Cheng Zhang, Dmitry Lyumkis, Timothy S. Baker, Navtej Toor;et al

Issue&Volume: 25 JULY 2019

Abstract: Group II introns are a class of retroelements that invade DNA through a copy-and-paste mechanism known as retrotransposition. Their coordinated activities occur within a complex that includes a maturase protein, which promotes splicing through an unknown mechanism. The mechanism of splice site exchange within the RNA active site during catalysis also remains unclear. We determined two cryo-EM structures at 3.6- resolution of a group II intron reverse splicing into DNA. These structures reveal that the branch-site domain VI helix swings 90°, enabling substrate exchange during DNA integration. The maturase assists catalysis through a transient RNA-protein contact with domain VI that positions the branch-site adenosine for lariat formation during forward splicing. These findings provide the first direct evidence of the role the maturase plays during group II intron catalysis. The domain VI dynamics closely parallel spliceosomal branch-site helix movement and provide strong evidence for a retroelement origin of the spliceosome.

DOI: DOI:https://doi.org/10.1016/j.cell.2019.06.035

Source: https://www.cell.com/cell/fulltext/S0092-8674(19)30738-X#