Date of Award

Spring 5-2013

Degree Type

Dissertation-Restricted

Degree Name

Ph.D.

Degree Program

Chemistry

Department

Chemistry

Major Professor

Liu, Zhengchang

Second Advisor

Schluchter, Wendy

Third Advisor

Rees, Bernard

Fourth Advisor

Trudell, Mark

Abstract

An integrative, biochemical, genetic, and molecular biology approach utilizing gene manipulation, gene knock outs, plasmid based protein expression, and in vivo protein localization of fluorescence tagged proteins was employed to determine the function of an essential protein, Lst8, in TORC1 and TORC2 signaling and a previously uncharacterized complex, the Far3-7-8-9-10-11 complex (Far complex) in the budding yeast, Saccharomyces cerevisiae. Mutations in SAC7 and FAR11 suppressed lethality of both lst8 and tor2-21 mutations but not TORC1 inactivation, suggesting that the essential function of Lst8 is linked only to TORC2.

Far11, a component of a six-member complex, was found to interact with Tpd3 and Pph21, conserved components of Protein Phosphatase 2A (PP2A) via co-immunoprecipitation. Mutations in FAR11 and RTS1, which encodes a PP2A regulatory B subunit, restore phosphorylation to the TORC2 substrate Slm1 in a tor2-21 mutant. These data suggest that TORC2 signaling is antagonized by Far11-dependent PP2A activity.

To characterize the assembly of the Far complex in vivo, intracellular localization of the Far complex was examined by fluorescence microscopy. It was found that the Far complex localizes to the endoplasmic reticulum (ER). The data show that Far9 and Far10 are tail-anchored proteins that localize to the ER first and recruit a Far8-Far7-Far3 pre-complex. Far11 is found at the ER only when all other Far proteins are assembled at the ER. Surprisingly, ER localization is required for the Far Complex’s role TORC2 signaling because deletion of the tail-anchor domain of Far9 results in partial bypass of the tor2-21 mutant growth defect at 37 ˚C.

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The University of New Orleans and its agents retain the non-exclusive license to archive and make accessible this dissertation or thesis in whole or in part in all forms of media, now or hereafter known. The author retains all other ownership rights to the copyright of the thesis or dissertation.

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