Syn61: Total Synthesis of E. coli with a Fully Recoded Genome - The Foundation of Constructive Bio's Platform
Fredens, J., Wang, K., de la Torre, D., Funke, L.F.H., Robertson, W.E., Christova, Y., Chia, T., Schmied, W.H., Dunkelmann, D.L., Beránek, V., Uttamapinant, C., Gonzalez Llamazares, A., Elliott, T.S., Chin, J.W.
Nature 569(7757), 514–518 (2019)
Constructive Bio's foundational technology began with Syn61, the first organism with a fully synthetic, radically recoded genome. Created by Professor Jason Chin's group at the MRC Laboratory of Molecular Biology in Cambridge, UK, the work was published in Nature in 2019.
The Syn61 project replaced the 4-million-base-pair E. coli genome with synthetic DNA in which all instances of three specific codons (TCG, TCA, and TAG) were systematically substituted with synonymous alternatives. This meant over 18,000 individual codon changes across the genome, executed without compromising cell viability. The result was a living organism with three codons unused anywhere in its genetic code, freeing them to be reassigned to new functions.
This differs fundamentally from earlier genetic code expansion approaches, which relied on amber suppression, a method that hijacks the TAG stop codon to insert a single non-canonical amino acid. Amber suppression competes with the cell's natural translation termination machinery, limiting both efficiency and the number of distinct ncAAs that can be incorporated. Syn61 removed this competition by deleting the codons and their associated transfer RNAs from the genome, creating dedicated "blank" codons with no residual cellular function.
The practical significance for therapeutic manufacturing is direct. Freed codons in Syn61-derived strains can be reassigned to encode non-canonical amino acids via engineered aminoacyl-tRNA synthetase/tRNA pairs, the molecular machinery that charges amino acids onto transfer RNAs. Because these codons have no competing function in the cell, ncAA incorporation proceeds with high fidelity at genetically defined positions.
Syn61 is the platform on which Constructive Bio's technology stack is built: BioForge biomanufacturing, the therapeutic pipeline spanning nine modalities, and ongoing genome engineering work including the subsequent development of Syn57.
Why it matters
Syn61 is the origin of Constructive Bio's programmable biology platform. By proving that an organism can survive with a compressed genetic code, this work created the 'blank codons' that Constructive Bio's BioForge platform now uses to encode non-canonical amino acids into peptide therapeutics at industrial scale. Every subsequent advance, from multi-ncAA incorporation to virus-resistant production strains, builds directly on Syn61.
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