Escherichia coli is a well-established and popular host for heterologous expression of proteins. The preference in the choice of synonymous codons (codon bias), however, might differ for the host and the original source of the recombinant protein, constituting a potential bottleneck in production. Codon choice affects the efficiency of translation by a complex and poorly understood mechanism. The availability of certain tRNA species is one of the factors that may curtail the capacity of translation. Here we provide a tRNA-overexpressing strategy that allows the resolution of the codon bias, and boosts the translational capacity of the popular host BL21(DE3) when rare codons are encountered. In the BL21(DE3)-derived strain, called SixPack, copies of the genes corresponding to the six least abundant tRNA species have been assembled in a synthetic fragment and inserted into a rRNA operon. This arrangement, while not interfering with the growth properties of the new strain, allows dynamic control of the transcription of the extra tRNA genes, providing significantly elevated levels of the rare tRNAs in the exponential growth phase. Results from expression assays of a panel of recombinant proteins of diverse origin and codon composition showed that the performance of SixPack surpassed that of the parental BL21(DE3) or a related strain equipped with a rare tRNA-expressing plasmid.

中文翻译：

---

通过解决密码子偏倚来增强大肠杆菌的翻译能力

大肠杆菌是成熟的，流行的蛋白质异源表达宿主。但是，对于同义密码子（密码子偏向）的选择偏好可能因重组蛋白的宿主和原始来源而异，构成了生产中的潜在瓶颈。密码子的选择会通过复杂且鲜为人知的机制影响翻译效率。某些tRNA种类的可用性是可能限制翻译能力的因素之一。在这里，我们提供了一种tRNA过表达策略，该策略可以解决密码子偏倚，并在遇到稀有密码子时提高流行宿主BL21（DE3）的翻译能力。在BL21（DE3）衍生的菌株SixPack中，与六个最不丰富的tRNA种类相对应的基因的多个拷贝已组装在合成片段中，并插入到rRNA操纵子中。这种安排虽然不干扰新菌株的生长特性，但可以动态控制多余tRNA基因的转录，从而在指数生长期显着提高了稀有tRNA的水平。一组来自不同来源和密码子组成的重组蛋白的表达分析结果表明，SixPack的性能超过了亲本BL21（DE3）或配备有罕见tRNA表达质粒的相关菌株的性能。在指数生长期，显着提高了稀有tRNA的水平。一组来自不同来源和密码子组成的重组蛋白的表达分析结果表明，SixPack的性能超过了亲本BL21（DE3）或配备有罕见tRNA表达质粒的相关菌株的性能。在指数生长期，显着提高了稀有tRNA的水平。一组来自不同来源和密码子组成的重组蛋白的表达分析结果表明，SixPack的性能超过了亲本BL21（DE3）或配备有罕见tRNA表达质粒的相关菌株的性能。