Ask any high school biology student how many bases our genetic material DNA has, and you'll get four as the answer: adenine (A), cytosine (C), guanine (G), and thymine (T).
But in a series of new studies published in Science, three teams have identified dozens of viruses that has swapped one of the bases in their DNA for a novel one called 2-aminoadenine, later dubbed 'Z'.
From Quanta Magazine:
The Z base looks like a chemical modification of A; it’s an adenine nucleotide with an extra attachment. But that modest change allows Z to form a triple hydrogen bond with T, which is more stable than the double bond that holds together A-T.
...
since the alterations were “at the deepest level of chemical organization,” [geneticist Philippe Marlière of the University of Evry in France] said, “my instinct told me this is not just an anecdote. This is a profound violation.”
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