Escherichia coli with a 57-codon genetic code

The near-universal genetic code uses 64 codons to encode the 20 canonical amino acids and protein synthesis. Here we designed and generated Escherichia coli with a 4 Mb synthetic genome in which we replaced known occurrences of six sense codons and a stop codon with synonymous codons. The resulting organism, Syn57, uses 55 codons to encode the 20 canonical amino acids.