Engineering the genetic code of an organism has been proposed to provide a firewall from natural ecosystems by preventing viral infections and gene transfer^1,2,3,4,5,6. However, numerous viruses and mobile genetic elements encode parts of the translational apparatus^7,8,9, potentially rendering a genetic-code-based firewall ineffective. Here we show that such mobile transfer RNAs (tRNAs) enable gene transfer and allow viral replication in Escherichia coli despite the genome-wide removal of 3 of the 64 codons and the previously essential cognate tRNA and release factor genes. We then establish a genetic firewall by discovering viral tRNAs that provide exceptionally efficient codon reassignment allowing us to develop cells bearing an amino acid-swapped genetic code that reassigns two of the six serine codons to leucine during translation. This amino acid-swapped genetic code renders cells resistant to viral infections by mistranslating viral proteomes and prevents the escape of synthetic genetic information by engineered reliance on serine codons to produce leucine-requiring proteins. As these cells may have a selective advantage over wild organisms due to virus resistance, we also repurpose a third codon to biocontain this virus-resistant host through dependence on an amino acid not found in nature¹⁰. Our results may provide the basis for a general strategy to make any organism safely resistant to all natural viruses and prevent genetic information flow into and out of genetically modified organisms.

有人建议对生物体的遗传密码进行工程设计，以通过防止病毒感染和基因转移来提供自然生态系统的防火墙^1,2,3,4,5,6。然而，许多病毒和移动遗传元件对翻译装置的部分进行编码^7,8,9，可能导致基于遗传密码的防火墙失效。在这里，我们表明，尽管在全基因组范围内去除了 64 个密码子中的 3 个以及之前必需的同源 tRNA 和释放因子基因，但这种移动转移 RNA (tRNA) 仍可在大肠杆菌中实现基因转移并允许病毒复制。然后，我们通过发现病毒 tRNA 来建立遗传防火墙，这些 tRNA 提供异常有效的密码子重新分配，使我们能够开发出带有氨基酸交换遗传密码的细胞，该遗传密码在翻译过程中将六个丝氨酸密码子中的两个重新分配为亮氨酸。这种氨基酸交换的遗传密码通过错误翻译病毒蛋白质组使细胞对病毒感染具有抵抗力，并通过工程依赖丝氨酸密码子产生需要亮氨酸的蛋白质来防止合成遗传信息的逃逸。由于这些细胞由于病毒抗性而可能比野生生物体具有选择性优势，因此我们还重新利用了第三个密码子，通过依赖自然界中未发现的氨基酸来生物遏制这种病毒抗性宿主¹⁰。我们的结果可能为使任何生物体安全地抵抗所有天然病毒并防止遗传信息流入和流出转基因生物体的总体策略提供基础。