Rare, full-length circular intron RNAs distinct from lariats have been reported in several species, but their biogenesis is not understood. We envisioned and tested a hypothesis for their formation using Saccharomyces cerevisiae, documenting full-length and novel processed circular RNAs from multiple introns. Evidence implicates a previously undescribed catalytic activity of the intron lariat spliceosome (ILS) in which the 3′-OH of the lariat tail (with optional trimming and adenylation by the nuclear 3′ processing machinery) attacks the branch, joining the intron 3′ end to the 5′ splice site in a 3′–5′ linked circle. Human U2 and U12 spliceosomes produce analogous full-length and processed circles. Postsplicing catalytic activity of the spliceosome may promote intron transposition during eukaryotic genome evolution.

中文翻译：

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内含子套索剪接体将套索转化为真正的圆圈：内含子转座的影响


与套索不同的稀有全长环状内含子RNA已在多个物种中报道过，但其生物发生机制尚不清楚。我们利用酿酒酵母设想并测试了它们形成的假设，记录了来自多个内含子的全长和新加工的环状RNA。有证据表明内含子套索剪接体 (ILS) 具有先前未描述的催化活性，其中套索尾部的 3'-OH（通过核 3' 加工机器进行可选的修剪和腺苷酸化）攻击分支，连接内含子 3' 末端至 3'–5' 连接环中的 5' 剪接位点。人类 U2 和 U12 剪接体产生类似的全长和加工过的环。剪接体的剪接后催化活性可能促进真核基因组进化过程中的内含子转座。