Measuring the tolerance of the genetic code to altered codon size.
Measuring the tolerance of the genetic code to altered codon size.
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DOI：
10.7554/elife.76941
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发表时间：
2022-03-16
期刊：
影响因子：
7.7
通讯作者：
Esvelt, Kevin M.
中科院分区：
文献类型：
--
作者：
DeBenedictis, Erika Alden;Soll, Dieter;Esvelt, Kevin M.
使用四碱基密码子的翻译发生在天然和合成系统中。是什么限制导致遗传密码普遍采用三重密码子而不是四重密码子？在这里，我们调查的大肠杆菌遗传密码的耐受性tRNA突变，增加密码子的大小。我们发现，从所有20个典型的isoacceptor类的tRNA可以转换为功能性的四联体tRNA（qtRNA）。许多这些选择性地纳入一个单一的氨基酸，以响应一个指定的四碱基密码子，证实了与质谱。然而，有效的四联体密码子翻译通常需要多个tRNA突变。此外，虽然tRNA在很大程度上服从四联体转换，但20种氨酰tRNA合成酶中只有9种耐受四联体反密码子。这些可能构成一个功能和相互正交的一套，但一个急剧限制的化学字母表可用于一个新生的所有四联体代码。我们的研究结果表明，选择三联密码子是因为它更简单和足够，而不是因为四联体密码子是不可实现的。这些数据为合成生物学家提供了一个蓝图，可以有意地设计一个全四联体扩展的遗传密码。
Translation using four-base codons occurs in both natural and synthetic systems. What constraints contributed to the universal adoption of a triplet codon, rather than quadruplet codon, genetic code? Here, we investigate the tolerance of the Escherichia coli genetic code to tRNA mutations that increase codon size. We found that tRNAs from all 20 canonical isoacceptor classes can be converted to functional quadruplet tRNAs (qtRNAs). Many of these selectively incorporate a single amino acid in response to a specified four-base codon, as confirmed with mass spectrometry. However, efficient quadruplet codon translation often requires multiple tRNA mutations. Moreover, while tRNAs were largely amenable to quadruplet conversion, only nine of the twenty aminoacyl tRNA synthetases tolerate quadruplet anticodons. These may constitute a functional and mutually orthogonal set, but one that sharply limits the chemical alphabet available to a nascent all-quadruplet code. Our results suggest that the triplet codon code was selected because it is simpler and sufficient, not because a quadruplet codon code is unachievable. These data provide a blueprint for synthetic biologists to deliberately engineer an all-quadruplet expanded genetic code.