A preliminary analysis of translation initiation has been carried out using the model system Drosophila melanogaster. These efforts have focussed on identifying the homolog of mammalian of mammalian eIF-4F, a complex of three subunits; eIF-4E which binds the mRNA cap, eIF-4A which has ATP-dependent RNA helicase activity, and eIF-4$ gamma$, of unknown function. Attempts to clone the genes encoding subunits of eIF-4F have led to the isolation of two novel genes. A molecular screen for members of the DEAD family of RNA helicases that includes eIF-4A led to the isolation of a gene which encodes the putative homolog of a yeast protein involved in ribosome assembly. From a complementation screen for suppressors of mutants of the Saccharomyces cerevisiae cap binding subunit, was isolated a Drosophila cDNA encoding a putative ribosomal protein, RpS15a, of the 40S subunit. Further characterization of the mechanism of suppression has shown that overexpression of RpS15a stabilizes the yeast eIF-4E protein suggesting a direct interaction between eIF-4E and the ribosome. Our work has shown that unlike the mammalian system, two cap binding proteins exist in Drosophila. The molecular analysis of cDNA clones encoding Drosophila eIF-4E suggests that the proteins result from alternatively spliced mRNAs expressed from a single gene. The biochemical characterization of Drosophila eIF-4A has shown that eIF-4A is part of a complex similar in size to mammalian eIF-4F but that unlike mammals, one eIF-4A protein is produced from a single gene and is regulated by phosphorylation. Phosphorylated eIF-4A is present in oocytes and early embryos but not in later embryos. Phosphorylated eIF-4A accumulates on the 48S initiation complex suggesting that a mechanism involving the post-translational regulation of eIF-4A affects the translation of maternal mRNAs in the oocyte and early embryo.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.29072 |
| Date | January 1995 |
| Creators | Lavoie, Cynthia |
| Contributors | Lasko, Paul F. (advisor) |
| 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 Biology.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001479853, proquestno: NN08126, Theses scanned by UMI/ProQuest. |
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