Orthogonal translation via evolution of a quadruplet-decoding ribosome

Twenty amino acids make proteins as we know them. Two minor exceptions, selenocysteine and pyrrolysine expand the list in a limited way, using translation termination codons (TGA and TAG) placed in proper context. In a step towards expanding the genetic code, and translating messenger RNAs in a way that is controlled at will, Chin and his colleagues designed "orthogonal" ribosomes (named ribo-Q1) and transfer RNAs that are able to read termination codons as unnatural amino acids. They further expanded the triplet code to a quadruplet code, permitting decyphering of a further set of unnatural amino acids. Because ribo-Q1 can read quadruplets the new genetic code could theoretically be expanded to permit the making of proteins with more than 200 types of amino acids.

Encoding multiple unnatural amino acids via evolution of a quadruplet-decoding ribosome