This earlier work discovering nucleotides X and Y might be interesting too (warning paywall): https://www.economist.com/science-and-technology/2019/01/19/addin

This earlier work discovering nucleotides X and Y might be interesting too (warning paywall): https://www.economist.com/science-and-technology/2019/01/19/adding-new-dna-letters-make-novel-proteins-possible https://www.economist.com/science-and-technology/2019/01/19/...