Understanding the molecular mechanisms of nonstop mRNA metabolism in Saccharomyces cerevisiae
Messenger RNA surveillance comprises pathways that selectively degrade abnormal transcripts. It is an important aspect in the maintenance of prokaryotic and eukaryotic gene expression, preventing deleterious effects that can be caused by the proteins these transcripts encode. Nonstop decay, a specific mRNA surveillance pathway, rapidly degrades mRNAs that lack in-frame termination codons. However, the molecular mechanisms of nonstop decay are not fully understood because normal and abnormal mRNAs are degraded by the same machinery. Thus, an important aspect of my research was to understand how the basal machinery recognizes and selectively degrades nonstop mRNAs. According to the model for nonstop decay, the ribosome translates to the end of the poly(A) tail of a nonstop transcript. The empty A-site of the ribosome is thought to be recognized by Ski7p. Ski7p recruits the exosome, a 3'-exoribonuclease, targeting the mRNA for rapid decay. Therefore, the focus of my research was to understand (1) the biological and functional significance of translation elongation to the end of the poly(A) tail, and (2) to expand the current model by identifying trans-acting factors and understanding their roles in the recognition of nonstop mRNAs using Saccharomyces cerevisiae as a model system. This work lead to the finding that yeast strains periodically survey their 3'-UTRs for novel protein sequences, and in doing so, can trigger nonstop decay, suggesting that the nonstop decay pathway is an evolutionarily conserved process that mitigates the effects caused by nonstop proteins. In addition, this work lead to the identification of 12 novel genes that affect the stability of two nonstop mRNA reporters. Further, an analysis of one of these genes has implicated an inositol polyphosphate sugar molecule as an inhibitor of nonstop decay, providing a potential drug-target to patients suffering from diseases caused by the generation of a nonstop mRNA.
Wilson, Marenda, "Understanding the molecular mechanisms of nonstop mRNA metabolism in Saccharomyces cerevisiae" (2007). Texas Medical Center Dissertations (via ProQuest). AAI3289985.