Nonsense-mediated mRNA decay (NMD), the destabilization of an otherwise stable mRNA by premature translation termination, is a conserved quality control pathway that exemplifies the interdependence of mRNA decay and protein synthesis. NMD has been extensively studied in multiple eukaryotes, particularly with respect to the nature of its substrates and the structures and interactions of its central regulators, Upf1, 2, and 3. In spite of these efforts many key mechanistic questions about this important regulatory pathway remain to be resolved. We have yet to understand the detailed differences between normal and premature termination or the molecular events by which the Upf proteins selectively target translating mRNAs containing premature termination codons (PTCs), promote mRNA destabilization, or enhance the disassembly of a poorly dissociable premature termination complex. In part, an understanding of these problems required new approaches that take into account the important roles played by components of the protein synthesis apparatus in implementing NMD. Using the yeast Saccharomyces cerevisiae as a model system, we have now established such approaches. We developed a selective ribosome profiling procedure that allows delineation of the specificity and timing of Upf factor association with translating ribosomes, combined the selective purification of Upf1-associated ribosomes with cryo-electron microscopy to localize Upf1 to a specific ribosomal domain, combined mass spectrometry and efficient purification of full-length proteins derived from nonsense codon readthrough to elucidate details of aberrant translation termination, and identified and characterized novel negative and positive regulatory elements, including two Upf1-binding sites, in the previously uncharacterized C- terminal domain of Dcp2, the catalytic component of the mRNA decapping enzyme. In the experiments of this proposal, we will follow up on these developments, addressing three principal research directions that seek to: i) define the mechanistic differences between premature and normal translation termination, ii) elucidate the function of ribosome-associated Upf proteins, and iii) determine the mechanism of decapping activation by Upf1 and other decapping activators. At the conclusion of these studies we anticipate being able to formulate an integrated model detailing the molecular events linking premature translational termination to targeted mRNA decay.

Public Health Relevance

The long-term goal of this project is an understanding of the molecular mechanisms that regulate nonsense-mediated mRNA decay (NMD), a cellular quality control mechanism that is triggered by premature termination of the process of protein synthesis. An understanding of NMD is particularly pertinent to public health because approximately 15% of all inherited disorders are attributable to nonsense mutations, i.e., genetic alterations which give rise to premature termination of protein synthesis. Drugs aimed at bypassing the effects of nonsense mutations are currently being evaluated in patients and our experiments have the potential to lead to improvements in these novel therapeutic modalities.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Unknown (R35)
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Special Emphasis Panel (ZGM1)
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Bender, Michael T
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University of Massachusetts Medical School Worcester
Schools of Medicine
United States
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He, Feng; Celik, Alper; Wu, Chan et al. (2018) General decapping activators target different subsets of inefficiently translated mRNAs. Elife 7:
Celik, Alper; He, Feng; Jacobson, Allan (2017) NMD monitors translational fidelity 24/7. Curr Genet 63:1007-1010
Jacobson, Allan (2017) The moment when translational control had a theory of everything. Nat Rev Mol Cell Biol 18:344
Celik, Alper; Baker, Richard; He, Feng et al. (2017) High-resolution profiling of NMD targets in yeast reveals translational fidelity as a basis for substrate selection. RNA 23:735-748