Almost all organisms assemble proteins from the same 20 natural building blocks, known as amino acids. But now, in a feat of genetic engineering, researchers have for the first time constructed an organism that synthesizes and incorporates a 21st amino acid into its proteins.
The modified version of the common bacterium Escherichia coli could be valuable to scientists investigating why life operates with 20 amino acids, rather than, say, 19 or 21, remarks Ryan Mehl, a member of the team that created the bacterium at the Scripps Research Institute in La Jolla, Calif.