Fig. 1.

Function of nonsense-mediated mRNA decay. Top A normal transcript consists of a 5′ cap, followed by a 5′ UTR, the ORF, a 3′ UTR, and a poly(A) tail. The ORF of a transcript with a normal termination codon is translated into a full length protein. Bottom A transcript carrying a premature termination codon (PTC) will host a shortened ORF as well as an elongated 3′ UTR. Instead of continuously translating the transcript into a truncated protein with possible deleterious function in the cell, the PTC-containing transcript will be degraded via NMD