mRNA localization and turnover in mutants of the small GTPase Arf1p of "Saccharomyces cerevisiae"

In this thesis, a microarray-based screen is described that was carried out to identify transcripts that undergo Arf1p-dependent transport to the ER. Several mRNAs were identified that acquire a different localization when Arf1p function is lost. Concomitantly, the amount of the corresponding proteins was increased. Since general translation was attenuated in the arf1 mutant but translating ribosomes at the ER were found to be maintained, a model is proposed in which specific mRNAs relocate to the ER to make them available for preferential translation under conditions of stress.
As one of the transcripts was found to localize asymmetrically in wild-type cells, its transport was characterized in greater detail. A model is described how this mRNA is targeted to its unusual localization, the distal pole of the mother cell, by cotranslational coupling to actin cables that undergo retrograde flow.
Finally, a series of experiments is described that help to define what distinguishes multiple P bodies induced in secretory mutants from the few bright granules that are observed after glucose starvation. It is shown that the appearance of multiple P bodies is linked to Ca2+, and a set of proteins is identified that is strictly required for formation of Ca2+-induced P bodies but is dispensable for P body induction under other conditions. In addition, it is demonstrated that different pathways for P body induction directly regulate P body number. In a final set of experiments, it is shown that P bodies are stably linked to the ER under all conditions tested.