Nonsense mediated decay

Nonsense mediated decay (NMD) is a cellular mechanism of mRNA surveillance to detect nonsense mutations and prevent the expression of truncated or erroneous proteins. NMD is triggered by exon-junction complexes (EJC), that have been formed during pre-RNA processing, being downstream of the nonsense codon. Normally, these EJCs are removed during the first round of translation of the mRNA, but in the case of a premature stop codon, they are still present on the mRNA. This is identified as a problem by NMD factors and the RNA is degraded, for example by the exosome complex.