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).
Now, the same scientists have used genetic engineering techniques to coerce more-complicated organisms into placing unnatural amino acids into proteins. Led by Peter G. Schultz of the Scripps Research Institute in La Jolla, Calif., the team created yeast cells that add one of five unnatural amino acids to their natural 20-piece construction set. To give the yeast this capability, the researchers altered the cells’ biochemical machinery that identifies amino acids and puts them into particular locations within a protein.