Aqk

Gene

Translation

Short defective protein

Short defective protein

Gln

Mutated glutamine-tRNA

Wild type anti-codon

Mutation

Glutamine-tRNA
Gln

Juag

Translation

Mutant glutamine-tRNA

Full length protein,

Gln inserted at nonsense codon

Full length protein,

Gln inserted at nonsense codon

FIGURE 13.26 Mechanism of Nonsense Suppression

A gene containing a nonsense codon suffers a premature stop during translation and a short defective protein is made. However, a tRNA whose anticodon is mutated (from GUC to AUC) can recognize the stop codon and insert an amino acid (glutamine in this case). A full length protein will be made that has only one amino acid different from the original wild type.

Mutant tRNA molecules are known that read stop codons and insert amino acids. This suppresses nonsense mutations.

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