Hijacking Translation Initiation for Synthetic Biology

Genetic code expansion (GCE) has revolutionized the field of protein chemistry. Over the past several decades more than 150 different noncanonical amino acids (ncAAs) have been co-translationally installed into proteins within various host organisms. The vast majority of these ncAAs have been incorporated between the start and stop codons within an open reading frame. This requires that the ncAA be able to form a peptide bond at the alpha-amine, limiting the types of molecules that can be genetically encoded. In contrast, the alpha-amine of the initiating amino acid is not required for peptide bond formation. Therefore, including the initiator position in GCE allows for co-translational insertion of more diverse molecules that are modified, or completely lacking an alpha-amine. This review explores various methods which have been used to initiate protein synthesis with diverse molecules both in vitro and in vivo.