终止密码子主要有哪几种（为终止密码子安排新任务）

【为终止密码子安排新任务，可能是一种普遍存在的新机制，有意思】Short tRNA anticodon stem and mutant eRF1 allow stop codon reassignment，接下来我们就来聊聊关于终止密码子主要有哪几种?以下内容大家不妨参考一二希望能帮到您!

终止密码子主要有哪几种

【为终止密码子安排新任务，可能是一种普遍存在的新机制，有意思】Short tRNA anticodon stem and mutant eRF1 allow stop codon reassignment

Ambar Kachale, Zuzana Pavlíková, …Julius Lukeš Show authors

Nature volume 613, pages751–758 (2023)Cite this article

Abstract

Cognate tRNAs deliver specific amino acids to translating ribosomes according to the standard genetic code, and three codons with no cognate tRNAs serve as stop codons. Some protists have reassigned all stop codons as sense codons, neglecting this fundamental principle1,2,3,4. Here we analyse the in-frame stop codons in 7,259 predicted protein-coding genes of a previously undescribed trypanosomatid, Blastocrithidia nonstop. We reveal that in this species in-frame stop codons are underrepresented in genes expressed at high levels and that UAA serves as the only termination codon. Whereas new tRNAsGlu fully cognate to UAG and UAA evolved to reassign these stop codons, the UGA reassignment followed a different path through shortening the anticodon stem of tRNATrpCCA from five to four base pairs (bp). The canonical 5-bp tRNATrp recognizes UGG as dictated by the genetic code, whereas its shortened 4-bp variant incorporates tryptophan also into in-frame UGA. Mimicking this evolutionary twist by engineering both variants from B. nonstop, Trypanosoma brucei and Saccharomyces cerevisiae and expressing them in the last two species, we recorded a significantly higher readthrough for all 4-bp variants. Furthermore, a gene encoding B. nonstop release factor 1 acquired a mutation that specifically restricts UGA recognition, robustly potentiating the UGA reassignment. Virtually the same strategy has been adopted by the ciliate Condylostoma magnum. Hence, we describe a previously unknown, universal mechanism that has been exploited in unrelated eukaryotes with reassigned stop codons. 根据标准遗传密码，同源 tRNA 将特定的氨基酸递送到翻译的核糖体上，并且有三个没有同源 tRNA 的密码子充当终止密码子。一些原生动物重新指派所有终止密码子作为感知密码子，忽略了这一基本原则。在这里，我们分析一个先前未描述的毛细虫Blastocrithidia Nonstop的7259个预测的蛋白编码基因中的终止编码子。我们发现在这个物种中，在表达水平较高的基因中，终止密码子被低估了，而UAA作为唯一的终止编码子。新的tRNAsGlu完全同源于UAG和UAA，以重新指派这些终止密码子，而UGA重新指派则通过缩短tRNATrpCCA的反义股从5个到4个碱基对（bp）来实现。根据遗传密码，典型的5-bp tRNATrp可以识别出UGG，而它的缩短版本4-bp变量则将色氨酸也纳入到UGA的读码框中。通过从B. Nonstop，Trypanosoma Brucei和Saccharomyces Cerevisiae制造出这两种变体并在最后两个物种中表达它们，我们记录了所有4-bp变体的明显高出读取。此外，编码B. Nonstop释放因子1的基因获得了一种特异性限制UGA识别的突变，可以有效地加强UGA的重新指派。类虫Condylostoma Magnum实现了同样的策略。因此，我们描述了一种以前未知的、普遍的机制，已被不同的真核生物用于重新指派停止密码子。

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