Different nuclease requirements for exosome-mediated degradation of normal and nonstop mRNAs

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 108; no. 6; pp. 2366 - 2371
• Main Authors: Schaeffer, Daneen, van Hoof, Ambro, Steitz, Joan A.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 08.02.2011; National Acad Sciences
• Subjects: Biological Sciences; Cellular biology; Codon, Terminator - genetics; Codon, Terminator - metabolism; Decay; Enzyme kinetics; Erythroid cells; Exosomes; Exosomes - genetics; Exosomes - metabolism; Fungal Proteins - genetics; Fungal Proteins - metabolism; Genetic mutation; Hooves; Journalism; Messenger RNA; Ribonucleases - genetics; Ribonucleases - metabolism; Ribonucleic acid; Ribosomes; RNA; RNA stability; RNA Stability - physiology; RNA, Fungal - genetics; RNA, Fungal - metabolism; RNA, Messenger - genetics; RNA, Messenger - metabolism; Saccharomyces cerevisiae - genetics; Saccharomyces cerevisiae - metabolism; stop codon; Yeast; Yeasts
• ISSN: 0027-8424; 1091-6490; 1091-6490
• DOI: 10.1073/pnas.1013180108

Two general pathways of mRNA decay have been characterized in yeast. In one pathway, the mRNA is degraded by the cytoplasmic form of the exosome. The exosome has both 3' to 5' exoribonuclease and endoribonuclease activity, and the available evidence suggests that the exonuclease activity is required for the degradation of mRNAs. We confirm here that this is true for normal mRNAs, but that aberrant mRNAs that lack a stop codon can be efficiently degraded in the absence of the exonuclease activity of the exosome. Specifically, we show that the endo-and exonuclease activities of the exosome are both capable of rapidly degrading nonstop mRNAs and ribozyme-cleaved mRNAs. Additionally, the endonuclease activity of the exosome is not required for endonucleolytic cleavage in no-go decay. In vitro, the endonuclease domain of the exosome is active only under nonphysiological conditions, but our findings show that the in vivo activity is sufficient for the rapid degradation of nonstop mRNAs. Thus, whereas normal mRNAs are degraded by two exonucleases (Xrnip and Rrp44p), several endonucleases contribute to the decay of many aberrant mRNAs, including transcripts subject to nonstop and nogo decay. Our findings suggest that the nuclease requirements for general and nonstop mRNA decay are different, and describe a molecular function of the core exosome that is not disrupted by inactivating its exonuclease activity.