小柯机器人

捷克科学院Julius Lukeš等研究人员合作发现，短tRNA反密码子茎和突变体eRF1允许终止密码子重新分配。相关论文于2023年1月11日在线发表在《自然》杂志上。

研究人员分析了以前未描述的锥虫类（即Blastocrithidia nonstop）的7259个预测蛋白质编码基因中的框内终止密码子。研究人员发现在这个物种中，框内终止密码子在高水平表达的基因中代表性不足，UAA作为唯一的终止密码子。与UAG和UAA完全同源的新tRNA^Glu的演化是为了重新分配这些终止密码子，而UGA的重新分配则是通过将tRNA^Trp_CCA的反密码子茎从5个碱基对缩短到4个碱基对（bp）的不同路径。常规5个碱基对的tRNA^Trp按照遗传密码的规定识别UGG，而其缩短的4个碱基对的变体则将色氨酸也纳入到UGA的框内。

通过从B. nonstop、Trypanosoma brucei和Saccharomyces cerevisiae中设计这两个变体并在后两个物种中表达，研究人员记录了所有4bp变体的明显较高读取率，从而模仿了这一演化转折。此外，一个编码B. nonstop释放因子1的基因获得了一个突变，专门限制了UGA的识别，有力地增强了UGA的重新分配。几乎同样的策略也被纤毛虫Condylostoma magnum所采用。因此，研究人员描述了一个以前未知的、普遍的机制，该机制在不相关的具有重新分配的终止密码子的真核生物中被利用。

研究人员表示，同源的tRNA根据标准的遗传密码向翻译的核糖体提供特定的氨基酸，而没有同源tRNA的三个密码子作为终止密码子。一些原生动物将所有的终止密码子重新分配为意义密码子，从而忽视了这个基本原则。

附：英文原文

Title: Short tRNA anticodon stem and mutant eRF1 allow stop codon reassignment

Author: Kachale, Ambar, Pavlkov, Zuzana, Nenarokova, Anna, Roithov, Adriana, Durante, Ignacio M., Miletnov, Petra, Zhonov, Kristna, Nenarokov, Serafim, Votpka, Jan, Horkov, Eva, Ross, Robert L., Yurchenko, Vyacheslav, Beznoskov, Petra, Paris, Zdenk, Valek, Leo Shivaya, Luke, Julius

Issue&Volume: 2023-01-11

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.

DOI: 10.1038/s41586-022-05584-2

Source: https://www.nature.com/articles/s41586-022-05584-2

Nature：《自然》，创刊于1869年。隶属于施普林格·自然出版集团，最新IF：69.504
官方网址：http://www.nature.com/
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