Premature translational termination triggers mRNA decapping

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Abstract
THE degradation of messenger RNA in eukaryotic cells is initiated by endonucleolytic cleavage1,2 or by shortening of the poly(A) tail3–6, which for some mRNAs activates a deadenylation-depen-dent decapping reaction7. One type of rapid mRNA degradation in eukaryotes is caused by premature termination of translation8,9. This turnover process prevents the translation of aberrant mRNAs10,11, may affect the abundance and splicing pattern of nuclear transcripts12,13, and may be involved in the aetiology of human genetic disease14. Here we show that premature translational termination in yeast triggers decapping, independent of deadenylation, thereby exposing the transcript to 5′-to-3′ degradation. Inactivation of the 5′-to-3′ exonuclease reveals an additional 3′-to-5′ pathway of mRNA turnover. These observations provide in vivo evidence for two new mechanisms of mRNA decay.