Figure 1.

Reprogramming the genetic code. (A) A central paradigm in molecular biology for the synthesis of proteins containing natural amino acids (coloured circles) may be engineered for the synthesis of proteins containing unnatural amino acids (coloured stars), and by extension of the synthesis of completely unnatural polymers. (B) Progress in reprogramming the genetic code. Natural amino acids are represented by coloured circles and unnatural amino acids by coloured stars. The vertical axis shows progress in incorporating unnatural amino acids into proteins, while the horizontal axis shows progress in incorporating unnatural amino acids in increasingly complex organisms. Red arrows represent steps that have been experimentally demonstrated.