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a mutation yielding the termination codon UAA, resulting in premature termination of a polypeptide chain. Compare: suppressor mutation.
a genetic alteration that causes the synthesis of polypeptide chain to terminate prematurely because the triplet of nucleotides that normally codes for the next amino acid in the chain becomes uracil-adenine-guanine, the sequence that signals the end of the chain. It is one of three possible nonsense mutations. See also amber mutation, opal mutation.