A suppressor allows translation to continue when otherwise a mutation would have stopped it. (a) In the wild type, a tRNA reads the codon UAC and translation continues. (b) Termination of translation. Here, the translation apparatus cannot go past a stop codon (UAG in this case), because no tRNA can recognize the UAG triplet. Instead, a release factor binds with the codon and protein synthesis ends, with the subsequent release of the polypeptide fragment. (c) A mutation alters the anticodon of a tyrosine tRNA so that this tRNA can now read the UAG codon. The suppression of the UAG codon by the altered tRNA now permits chain elongation.
ANIMATED ART: Nonsense suppression of th e rodns allele, The tRNA nonsense suppressor, The rodns nonsense mutation