Expanded DNA alphabet: The GATC nucleotides have two new companions

All organisms on earth carry a blue-print of their construction in each cell. This blue-print is a genetic code written into either RNA or DNA and this code is transmitted to the next generation. Only viruses contain RNA, all other organisms contain DNA in every cell which is made up by four bases: guanine, cytosine, adenine and thymine. As seen in the figure, these bases form stable basepair bridges linking the two DNA strands together. Adenine only basepairs with thymine and guanine basepairs only with cytosine. All the cellular components required for copying DNA or translating the DNA code into proteins have only ever worked with the GATC bases.

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But yesterday a paper was published by Malyshev et al. that shows that new synthetically produced bases can form basepairs and that these bases can be stably inserted in a stretch of DNA called a plasmid. This plasmid containing the ordinary GATC but also the new bases, is put into E. coli bacteria, which can then replicate the plasmid accurately when provided with the synthetic nucleotides. This means that the E. coli cellular replication machinery can also work with the synthetic bases, making this the first time that it has been shown that synthetic basepairs can be integrated into newly replicated plasmids in a cell!

Extra reading: 
Nature News & Views | Synthetic biology: New letters for life's alphabet ​