Since at least the last common ancestor of all life on Earth, genetic information has been stored in a four-letter alphabet that is propagated and retrieved by the formation of two base pairs. The central goal of synthetic biology is to create new life forms and functions1, and the most general route to this goal is the creation of semi-synthetic organisms whose DNA harbours two additional letters that form a third, unnatural base pair. Previous efforts to generate such semi-synthetic organisms2 culminated in the creation of a strain of Escherichia coli that, by virtue of a nucleoside triphosphate transporter from Phaeodactylum tricornutum, imports the requisite unnatural triphosphates from its medium and then uses them to replicate a plasmid containing the unnatural base pair dNaM–dTPT3. Although the semi-synthetic organism stores increased information when compared to natural organisms, retrieval of the information requires in vivo transcription of the unnatural base pair into mRNA and tRNA, aminoacylation of the tRNA with a non-canonical amino acid, and efficient participation of the unnatural base pair in decoding at the ribosome. Here we report the in vivo transcription of DNA containing dNaM and dTPT3 into mRNAs with two different unnatural codons and tRNAs with cognate unnatural anticodons, and their efficient decoding at the ribosome to direct the site-specific incorporation of natural or non-canonical amino acids into superfolder green fluorescent protein. The results demonstrate that interactions other than hydrogen bonding can contribute to every step of information storage and retrieval. The resulting semi-synthetic organism both encodes and retrieves increased information and should serve as a platform for the creation of new life forms and functions.
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NCBI Reference Sequence
We thank P. G. Schultz for the pEVOL-pAzF plasmid. This work was supported by the National Institutes of Health (GM118178 to F.E.R.). A.W.F. was supported by a National Science Foundation Graduate Research Fellowship (NSF/DGE-1346837).
Extended data figures
Extended data tables
This file contains annotated sequences of plasmids denoted in Supplementary Table 1 suitable for direct import into sequence analysis software.
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The Standard Genetic Code can Evolve from a Two-Letter GC Code Without Information Loss or Costly Reassignments
Origins of Life and Evolution of Biospheres (2018)