Every living thing on Earth stores the instructions for life as DNA, using the four genetic bases A, G, C, and T.
All except one, that is.
In the San Diego laboratory of Floyd Romesberg—and at a startup he founded—grow bacteria with an expanded genetic code. They have two more letters, an “unnatural” pair he calls X and Y.
Romesberg, head of a laboratory at the Scripps Research Institute, first amended the genes of the bacterium E. Coli to harbor the new DNA components in 2014. Now, for the first time, the germs are using their expanded code to manufacture proteins with equally unusual components.
“We wanted to prove the concept that every step of information storage and retrieval could be mediated by an unnatural base pair,” he says. “It’s not a curiosity anymore.”
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