a mutation yielding the termination codon UGA, resulting in premature termination of a polypeptide chain. Compare: suppressor mutation.
Synonym(s): opal mutation
a genetic alteration that causes the synthesis of a 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. One of the three possible nonsense mutations. See also amber mutation, ochremutation.