"[T]wo groups of scientists are reporting for the first time that two new nucleotides can do the same thing – raising the possibility that entirely new proteins could be created for medical uses.
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Millie M. Georgiadis, Steven A. Benner and colleagues from Indiana and Florida wanted to see if another potential set of letters, "Z" (6-amino-5-nitro-2(1H)-pyridone) and "P" (2-amino-imidazo[1,2-a]-1,3,5-triazin-4(8H)one), would form a helix – and evolve.
The researchers found that multiple Z-P pairs can contribute to a double helix, just as C-G and A-T pairs do, with the same combination of flexibility and rigidity required for natural DNA to function. They also showed that the Z-P pairs integrate well with conventional pairs and that six-letter GACTZP DNA can evolve."
http://www.sciencedaily.com/releases/2015/05/150527113101.htm