Adding new DNA letters make novel proteins possible

THE FUZZYDNAACTGDNAATCGXY specks growing on discs of jelly in Floyd Romesberg’s lab at Scripps Research in La Jolla look much like any other culture of . But appearances deceive—for the of these bacteria is written in an alphabet that has six chemical letters instead of the usual four.Every other organism on Earth relies on a quartet of genetic bases: (adenine), (cytosine), (thymine) and (guanine). These fit together in pairs inside a double-stranded molecule, matching and , . But in 2014 Dr Romesberg announced that he had synthesised a new, unnatural, base pair, dubbed and , and slipped them into the genome of as well.