Amber Suppression: a Nucleotide Change in the Anticodon of a Tyrosine Transfer RNA

In certain mutants a single base change alters the meaning of a messenger codon in such a way that, instead of spelling out an amino-acid, it spells out chain termination. Mutants in a quite different gene, called a suppression gene, allow the chain-terminating triplet to be read as an amino-acid. Experiments have shown that this is caused by a mutated tRNA which carries a single base change in its anticodon. This allows it to read the chain-terminating codon as if it spelt tyrosine.