Translational control is crucial to balancing the cell's protein output and genetic expression. The substrate of the translational machinery---messenger RNA (mRNA)---is itself subject to regulation. The lifetime of an mRNA is limited and therefore mRNA decay is a critical step in the regulation of gene expression. Translation and mRNA decay are intimately related processes as they both handle the cell economy. mRNAs are generally in a balancing act between the translational and the repression/decay machinery, which ultimately decides the fate of an mRNA and its protein expression rate. In fact, translation affects the rate of mRNA decay. For instance, aberrant messages which contain a premature-termination codon (PTC) require ribosome scanning in order to read the message, discover the mistake, and essentially prompt its destruction. Here, a relationship between the nuclear translation-like factor---eIF4AIII, the nuclear import factor of cIF4E---4E-T, and mRNA decay was discovered. eIF4AIII is a nuclear protein that interacts physically or functionally with translation initiation factors eIF4G and eIF4B, respectively, and shares strikingly high identity with the initiation factors eIF4AI/II. This work demonstrates that eIF4AIII but not eIF4AI is required for nonsense-mediated decay (NMD). NMD is a surveillance mechanism in eukaryotes which degrades the mRNA when a PTC is present. NMD is a splicing and translation-dependent event in mammalians. We show eIF4AIII is deposited at the exon-exon junction during splicing, is a shuttling protein, and is necessary for NMD. At steady state, 4E-T is predominantly cytoplasmic and is concentrated in bodies that conspicuously resemble the recently described Processing bodies (P-bodies), which are sites of mRNA decay. We demonstrate that 4E-T colocalizes with mRNA decapping factors in bona fide P-bodies and that its binding partner, eIF4E, is tethered to P-bodies in a 4E-T dependent manner. Moreover, 4E-T controls mRNA half life. We demonstrate that 4E-T interaction with eIF4E represses translation, which is thought to be a prerequisite for targeting of mRNAs to P-bodies. Hence, analysis of prospective translation factors has led to elucidation of mRNA decay pathways.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.103156 |
| Date | January 2006 |
| Creators | Ferraiuolo, Maria A. |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Biochemistry.) |
| Rights | © Maria A. Ferraiuolo, 2006 |
| Relation | alephsysno: 002584276, proquestno: AAINR32350, Theses scanned by UMI/ProQuest. |
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