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Importantly they also discovered all five nitrogenous bases — adenine, guanine, cytosine, thymine, and uracil — that are necessary to build DNA and RNA.

One loose end, Sasselov acknowledges, is that RAO has only been shown to lead to the synthesis of two of RNA’s four nucleotides, cytosine and uracil.

RNA, short for ribonucleic acid, would not be possible without uracil.

Rather than inducing random changes in the virus’ RNA genome, the drug is more likely to cause specific nucleic acid substitutions, with guanine switching to adenine and cytosine to uracil.

“I am uncertain what it was finally, natural uracil or only dose or both,” he says.