Abstract

The expression of protein‐encoding genes is a complex process culminating in the production of mature mRNA and its translation by the ribosomes. The production of a mature mRNA involves an intricate series of processing steps. The majority of eukaryotic protein‐encoding genes contain intron sequences that disrupt the protein‐encoding frame, and hence have to be removed from immature mRNA prior to translation into protein. The mechanism involved in the selection of correct splice sites is incompletely understood. A considerable body of evidence suggests that the splicing machinery has suboptimal efficiency and fidelity leading to substantial processing inaccuracy. Here we discuss a recently published article1 that extends observations that cells rely on nonsense‐mediated mRNA decay (NMD) to compensate for such suboptimal processing accuracy. Intriguingly these authors provide evidence for a strong selective pressure in favour of premature termination of mRNA translation in the event of intron retention. The analysis presented implies a positive role of NMD in transcript diversification through alternative splicing and suggest that this ancient surveillance mechanism may have co‐evolved with intron acquisition born from the need for quality control of splicing patterns. BioEssays 30:926–928, 2008. © 2008 Wiley Periodicals, Inc.