Mechanisms of nuclear mRNA quality control.

Nuclear processing, packaging and export of mRNA transcripts are highly complex and coupled steps in eukaryotic gene expression that require mRNA quality control. During transcription, mRNAs must be capped, spliced and polyadenylated by processing factors. The processed mRNAs must also be loaded with numerous mRNA packaging and export factors to facilitate transport through nuclear pore complexes to the cytoplasm for translation. Given such complexity, mRNA production errors can lead to improperly processed/packaged mRNA transcripts that may be harmful to the cell if they are translated into defective proteins or deplete a functionally important gene product. To combat these aberrant mRNA transcripts, eukaryotic cells have evolved several nuclear and cytoplasmic mRNA quality control mechanisms that recognize and degrade incorrectly processed/packaged transcripts. Here we review recent progress in understanding evolutionarily conserved nuclear mRNA quality control mechanisms in the yeast Saccharomyces cerevisiae with particular emphasis on a novel mRNA quality control step at the nuclear pore.