How Unique Is the Genetic Code?

Abstract

Sometimes, less is more. The genetic code seems to be reduced and was probably optimized during evolution. This idea is supported by the newly discovered amino acid pyrrolysine (see scheme, X=Me, NH2, OH) as an essential side chain in the active site of a methyl transferase in Archaea. The chemical and structural properties of pyrrolysine, which is directly encoded by redefining a stop codon, are discussed with regard to the “universality” of the genetic code.