tRNA engineering for manipulating genetic code

In ribosomal translation, only 20 kinds of proteinogenic amino acids (pAAs), namely 19 l-amino acids and glycine, are exclusively incorporated into polypeptide chain. To overcome this limitation, various methods to introduce non-proteinogenic amino acids (npAAs) other than the 20 pAAs have been developed to date. However, the repertoire of amino acids that can be simultaneously introduced is still limited. Moreover, the efficiency of npAA incorporation is not always sufficient depending on their structures. Fidelity of translation is sometimes low due to misincorporation of competing pAAs and/or undesired translation termination. Here, we provide an overview of efforts to solve these issues, focusing on the engineering of tRNAs.