Rare codons generally arrest translation due to rarity of their cognate tRNAs. This property of rare codons can be utilized to regulate protein expression. In this study, a linear relationship was found between expression levels of genes and copy numbers of rare codons inserted within them. Based on this discovery, we constructed a molecular device in Escherichia coli using the rare codon AGG, its cognate tRNA (tRNA(Arg) (CCU)), modified tRNA(Asp) (GUC → CCU), and truncated aspartyl-tRNA synthetase (TDRS) to switch the expression of reporter genes on or off as well as to precisely regulate their expression to various intermediate levels. To underscore the applicability of our work, we used the rare codon device to alter the expression levels of four genes of the fatty acid synthesis II (FASII) pathway (i.e. fabZ, fabG, fabI, and tesA') in E. coli to optimize steady-state kinetics, which produced nearly two-fold increase in fatty acid yield. Thus, the proposed method has potential applications in regulating target protein expression at desired levels and optimizing metabolic pathways by precisely tuning in vivo molar ratio of relevant enzymes.

中文翻译：

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工程化的稀有密码子设备，可优化代谢途径。

由于稀有密码子的同源tRNA很少，因此通常会阻止翻译。稀有密码子的这种特性可用于调节蛋白质表达。在这项研究中，发现基因的表达水平和插入其中的稀有密码子的拷贝数之间存在线性关系。基于这一发现，我们使用稀有密码子AGG，其同源tRNA（tRNA（Arg）（CCU）），修饰的tRNA（Asp）（GUC→CCU）和截短的天冬氨酰tRNA合成酶（ TDRS）来打开或关闭报告基因的表达，以及将其表达精确地调节到各种中间水平。为了强调我们研究的适用性，我们使用了稀有密码子设备来改变脂肪酸合成II（FASII）途径的四个基因（即fabZ，fabG，fabI和tesA'）在E中的表达水平。大肠杆菌可优化稳态动力学，从而使脂肪酸收率提高近两倍。因此，提出的方法在通过精确调节相关酶的体内摩尔比来调节目标蛋白的表达水平和优化代谢途径方面具有潜在的应用价值。