DNA, the blueprint of life, is made up of four nucleic acids: Adenine (A), Thymine (T), Cytosine (C) and Guanine (G). These nucleotides form long strands of DNA by forming base pairs: A with T and C with G. From the genetic code made up of these four, simple nucleotides, we have all the diversity of life as we know it. Now, researchers have expanded on that diversity, by creating two synthetic nucleotides capable of replicating in a live cell.
While many artificial nucleotides have been made, the researchers previously found that a particular pair, d5SICS and dNaM, was able to integrate into DNA and replicate in a test tube.
In order to test whether these nucleotides can integrate into live cells, they engineered special E. Coli with unique transporters that import the novel nucleotides into the cell. Then, they introduced a plasmid with just one base pair replaced with d5SICS-dNAM.
Now here's where it gets a little tricky. E. Coli DNA is normally replicated with a protein called polymerase III, while their base pair has been shown to work quite well with polymerase I. So, to bolster their chances of success, they purposely placed their base pair in a region of the plasmid which should only be replicated by polymerase I.
With these modifications in place, they placed their engineered E. Coli into culture media containing d5SICS and dNAM and found that the bacteria successfully grew and properly integrated d5SICS-dNAM into newly synthesized DNA. Importantly, they found that the artificial nucleotides were not removed by DNA repair mechanisms, and were only lost as the DNA naturally mutated.
Of course, a lot remains to be seen as to whether d5SICS-dNAM can be integrated into more diverse areas of a genome, whether it can be transcribed into RNA, and whether this can be used to create a new code with different amino acids.
With all these special modifications to make this work, I doubt we'll be seeing anything like this in higher organisms soon =P. But! This shows that expanding the genetic code is possible, and who knows what possibilities will be discovered with further experimenting.
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