Nonsense mutation
A mutation (a change) in a base in the DNA that prematurely stops the translation (reading) of messenger RNA (mRNA) resulting in a polypeptide chain that ends prematurely and a protein product that is truncated (abbreviated) and incomplete and usually nonfunctional. The nonsense mutation converts a codon (a triplet of bases) that encodes an amino acid into a stop codon, one that specifies the termination of translation. There are three nonsense codons (UAG, UAA, and UGA) in mRNA. One of them comes normally at the end of each polypeptide. A nonsense codon is a stop codon which is out of place. Catching such a defective messenger RNA (mRNA) before a truncated and potentially harmful protein is synthesized is the job of what is called the nonsense-mediated mRNA decay (NMD) pathway.
* * *
a mutation in which one of the three termination codons in the mRNA (UAG, amber; UAA, ochre; UGA, umber or opal), used to signal the end of a polypeptide, appears in the middle of a genetic message, causes premature termination of transcription, and results in the production of an incomplete, generally nonfunctional polypeptide. See also missense m.
Medical dictionary.
2011.