Regulation of the Ste4p G protein beta subunit activity in the pheromone response pathway of Saccharomyces cerevisiae.
Item
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Title
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Regulation of the Ste4p G protein beta subunit activity in the pheromone response pathway of Saccharomyces cerevisiae.
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Identifier
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AAI9908335
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identifier
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9908335
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Creator
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Kim, Jinah.
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Contributor
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Adviser: Jeanne P. Hirsch
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Date
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1998
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Language
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English
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Publisher
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City University of New York.
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Subject
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Biology, Molecular | Biology, Cell | Biology, Genetics
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Abstract
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The pheromone response in Saccharomyces cerevisiae is activated by the binding of pheromone to its receptor, which belongs to the G protein-coupled receptor family. The G{dollar}\beta\gamma{dollar} complex transduces the signal in the pheromone response, which results in arrest in the G{dollar}\sb1{dollar} phase of the cell cycle, transcriptional activation of mating-specific genes, and cellular morphogenesis.;The mechanism of receptor-mediated heterotrimeric G-protein activation has been thoroughly investigated. However, the regulatory mechanisms controlling G{dollar}\beta\gamma{dollar} complex activity subsequent to dissociation from G{dollar}\alpha{dollar}-GTP are not well-understood. The goal of this work was to investigate mechanisms of regulating G{dollar}\beta\gamma{dollar} activity in the pheromone response pathway through (1) characterization of Ste4p-mediated receptor inhibition and (2) identification of the mating function of SSF1.;The STE3{dollar}\sp{lcub}DAF{rcub}{dollar} mutation results in the inappropriate expression of a-factor receptor (Ste3p) in MATa cells. Expression of this receptor inhibits pheromone-induced cell cycle arrest, a phenomenon termed receptor inhibition. STE4{dollar}\sp{lcub}SD{rcub}{dollar} alleles were isolated which were able to reverse receptor inhibition. The Ste4p{dollar}\rm\sp{lcub}SD{rcub}{dollar} was capable of restoring both pheromone-mediated cell cycle arrest and transcriptional activation in STE3{dollar}\sp{lcub}DAF{rcub}{dollar} cells. To identify the mechanism of Ste4p-mediated receptor inhibition the localization of Ste4p was observed in STE3{dollar}\sp{lcub}DAF{rcub}{dollar} cells. The Ste4p-GFP fusion protein appeared to be differentially localized in STE3{dollar}\sp{lcub}DAF{rcub}{dollar} cells compared to wild type cells after pheromone exposure. The results suggest that G-protein signaling may be controlled through regulating the G{dollar}\beta\gamma{dollar} localization in response to different signals from the cell surface.;Characterization of the mating function of SSF1 was also examined. SSF1 and SSF2 are redundant essential genes, which when overexpressed, results in increased mating efficiency in a strain containing a defective G{dollar}\beta{dollar} subunit. Overexpression of SSF1 resulted in increased mating projection formation. Cells depleted of Ssfp proteins were defective in projection formation. These results suggested that Ssf1p may increase mating efficiency through regulating cellular morphogenesis. A Ssf1p-GFP fusion demonstrated nucleolar localization, which suggested that Ssf1p may indirectly promote projection formation.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
