A synthetic Escherichia coli bacterium that can make all of the usual amino acids using a restricted set of instructions for making proteins is reported online in Nature this week. The study paves the way for researchers to design synthetic bacteria that have useful and unusual features.
The genetic code is made up of four different chemical bases or nucleotides, called A, C, G and T. The order of these nucleotides forms a three-letter code, where each trio or ‘codon’ stands for either the insertion of a particular amino acid or a signal to stop making the protein. There are 64 different codons, but only 20 different amino acids, so multiple codons stand for individual amino acids. This means that there is inherent redundancy in the genetic code.
Jason Chin and colleagues have recoded the entire E. coli genome to produce an organism that uses 59 codons rather than the full set of 61 to make all of the normal amino acids; in addition, they recoded one of the three stop codons. The study reveals that the genetic code can be compressed and that bacterial life is still possible even when certain codons are absent. In the future, these missing codons could be replaced with novel sequences that encode non-natural amino acids, creating opportunities for researchers to design synthetic bacteria that make non-natural biopolymers.