Amending the Genetic Code: Yeast adds new amino acids to its proteins

With only rare exceptions, every organism constructs proteins from just 20 building blocks called amino acids. Recently, however, researchers modified Escherichia coli bacteria so that the single-celled organisms also make an alien amino acid and incorporate it into proteins (SN: 1/25/03, p. 53: Available to subscribers at Unnatural Biochemistry: Bacteria make and use an alien amino acid).