The SAC1p, an integral membrane protein involved in secretory pathway function and actin function in Saccharomyces cerevisiae
Cleves, Ann Elizabeth
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Permalink
https://hdl.handle.net/2142/22832
Description
Title
The SAC1p, an integral membrane protein involved in secretory pathway function and actin function in Saccharomyces cerevisiae
Author(s)
Cleves, Ann Elizabeth
Issue Date
1992
Doctoral Committee Chair(s)
Bankaitis, Vytas A.
Department of Study
Microbiology
Discipline
Microbiology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Molecular
Biology, Cell
Biology, Microbiology
Language
eng
Abstract
The secretory pathway of the yeast Saccharomyces cerevisiae is strictly analogous to that of mammalian cells. Proteins destined for secretion are transported in a vectorial fashion from the endoplasmic reticulum to the Golgi apparatus to the cell surface. Superimposed on the normal flow of secretory traffic in yeast is a level of spatial organization. Golgi-derived secretory vesicles are directed to a defined region of the mother cell surface known as the bud. During the budding portion of the cell cycle, secretion and cell surface growth are coincident which results in the selective growth of the bud. The actin cytoskeleton has been implicated as the mediator of the polarized mode of yeast cell growth. The filamentous actin cytoskeleton consists of two structures, asymmetrically-arranged cortical patches and cables which are aligned along the mother cell-bud axis. Structural analyses indicated that the patches could participate in localized membrane growth while the cables are correctly positioned to be involved in directed vesicular transport. Given the proposed relationship between secretion and actin, it seems reasonable that there would be communication between the secretory pathway and the actin cytoskeleton in yeast. Presented in this thesis is evidence that the S. cerevisiae SAC1 gene product could represent one aspect of the mechanism for coupling secretory pathway function and actin assembly in yeast. Mutations in SAC1 were isolated as extragenic suppressors of both Golgi and actin defects. Analysis of the SAC1 gene product revealed that the SAC1p was a 71kD integral membrane protein that exhibited a small cytoplasmic domain. The SAC1p localized to yeast ER and Golgi membranes, but showed no obvious association with the filamentous actin cytoskeleton. Native immunoprecipitation experiments suggested that the SAC1p was an actin binding protein in yeast. Finally, a model is proposed which reconciles how the SAC1p could be involved in the activities of both the secretory pathway and actin cytoskeleton, thereby rendering the SAC1p capable of participating in the spatial restriction imposed on secretory traffic in yeast.
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