冷冻电镜结构揭示了 II 类内含子反向剪接进入 DNA。
Cryo-EM Structures of a Group II Intron Reverse Splicing into DNA.
机构信息
Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093, USA.
Salk Institute, La Jolla, CA 92037, USA.
出版信息
Cell. 2019 Jul 25;178(3):612-623.e12. doi: 10.1016/j.cell.2019.06.035.
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-Å 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.
内含子 II 是一类通过逆转录转座机制（即复制粘贴机制）入侵 DNA 的反转录元件。它们的协调活动发生在一个包含成熟酶蛋白的复合物中，该蛋白通过未知机制促进剪接。在催化过程中，RNA 活性位点内的剪接位点交换的机制也不清楚。我们通过对一个 3.6-Å 分辨率的内含子 II 反向剪接进入 DNA 的冷冻电镜结构测定，确定了两个结构。这些结构表明，分支位点结构域 VI 螺旋摆动 90°，从而在 DNA 整合过程中实现了底物交换。成熟酶通过与结构域 VI 的短暂 RNA-蛋白质接触辅助催化，使分支位点腺苷在正向剪接过程中形成套索。这些发现为成熟酶在内含子 II 催化过程中的作用提供了第一个直接证据。结构域 VI 的动力学与剪接体分支位点螺旋运动密切平行，为剪接体的反转录元件起源提供了有力证据。
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