Characterizing Molecular Pathways that Rescue Stalled Ribosomes and Decay Problematic Messenger RNAs
DORAZIO-DISSERTATION-2020.pdf (6.986Mb) (embargoed until: 2021-05-01)
D'Orazio, Karole Nicole
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Translation through problematic sequences in mRNAs leads to ribosome collisions that trigger a collection of quality control events including ribosome rescue, degradation of the stalled nascent polypeptide via the Ribosome-mediated Quality control Complex (RQC), and targeting of the mRNA for decay (No Go Decay or NGD). Using reverse genetic screens in yeast, we identify Cue2 as the key endonuclease that is recruited to stalled ribosomes to promote NGD. Following Cue2-mediated cleavage, ribosomes upstream of the cleavage site translate to the end of the truncated mRNA and are rescued by the Dom34:Hbs1 complex. We also show that the putative helicase Slh1 reduces ribosome occupancy on intact problematic mRNAs and thereby reduces endonucleolytic cleavage by Cue2. The synergistic activities of Cue2 and Slh1 define two parallel pathways that allow cells to recognize and respond to ribosomes trapped on problematic mRNAs. From the same study in yeast, we also identify a set of novel candidate genes that act on NGD-substrates. In preliminary experiments we note that these factors are involved in many different processes involving translation elongation, deubiquitination processes, and mRNA decay and future work will further characterize these genes.