In a paper published in the journal Nature, bioengineers at The Scripps Research Institute in the San Diego neighborhood of La Jolla said they had successfully inserted two synthetic molecules into the genome of an Escherichia coli bacterium, which survived and passed on the new genetic material. In addition to the naturally occurring nucleotides adenine, thymine, guanine and cytosine, which form the rungs of DNA’s double-helix structure, the bacterium carried two more base-pair partners, which study authors have dubbed d5SICS and dNaM. For more than a decade, scientists have been experimenting with so-called unnatural base pairs, or UBPs, saying they...