| Summary: | Translational control is an important means of regulating gene expression. Development of the Drosophila germ line relies on translational regulation to differentially express maternal mRNAs, allowing it to develop distinctly from the soma. One of the critical factors required for germ cell development and function is the conserved DEAD-box RNA helicase Vasa (Vas). The research presented in this thesis examines the role of Vas in translational regulation during Drosophila germ line development. A two-hybrid screen conducted with Vas identified a translation initiation factor eIF5B (dIF2), as a direct interactor. Mutations were created in eIF5B and were found to enhance the vas mutant phenotypes of reduced germ cell numbers, and posterior segmentation defects, suggesting a functional interaction between these factors in vivo. In order to further understand the biological significance of the Vas-eIF5B interaction, the region of Vas required for eIF5B-binding was mapped and then specifically disrupted. Reduction of Vas-eIF5B binding using a transgenic approach, virtually eliminated germ cell formation, while having only a moderate effect on the somatic requirement of Vas in posterior segmentation. In addition, Vas-eIF5B interaction was found to be required for the establishment of polarity within the egg during oogenesis, likely through direct regulation of gurken (grk) mRNA. We concluded that through interaction with eIF5B, Vas plays a critical role in translational regulation in the germ line. In addition, another Drosophila DEAD-box protein, highly similar to Vas, called Belle (Bel) was characterized. Mutations in bel were found to also affect the germ line, leading to both female and male sterility. Like Vas, Bel is implicated in translation initiation, however bel is an essential gene, with a requirement for growth, whose function is not restricted to the germ line. Our data suggest that Bel may be a nucleocytoplasmic shuttling protein,
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