when a ribosome encounters a premature termination codon

In mammalian cells, aberrant transcripts harboring a prematuretermination codon (PTC) can be generated by abnormal orinefficient biogenesis of mRNAs or by somatic mutation.Truncated polypeptides synthesized from these aberranttranscripts could be toxic to normal cellular functions. However,mammalian cells have evolved sophisticated mechanismsfor monitoring the quality of mRNAs. The faultytranscripts harboring PTC are subject to nonsense-mediatedmRNA decay (NMD), nonsense-mediated translational repression(NMTR), nonsense-associated alternative splicing (NAS),or nonsense-mediated transcriptional gene silencing (NMTGS).In this review, we briefly outline the molecular characteristicsof each pathway and suggest mRNA quality controlmechanisms as a means to regulate normal gene expression.[BMB Reports 2013; 46(1): 9-16]