Suppression of a nonsense mutation. (a) The wild-type mRNA encodes a full-length protein, with CAG encoding Gln (glutamine). (b) A nonsense mutation at an internal CAG codon changes it to a UAG termination codon, resulting in an incomplete protein. (c) A tRNA^Tyr suppressor has a mutant anticodon that pairs with the UAG nonsense (stop) codon, resulting in a full-length protein with a Tyr residue in place of the Gln residue of the wild-type protein.