Structural and functional characterization of the maltose transporter of Saccharomyces.
Item
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Title
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Structural and functional characterization of the maltose transporter of Saccharomyces.
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Identifier
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AAI9218229
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identifier
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9218229
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Creator
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Cheng, Qi.
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Contributor
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Adviser: Corinne A. Michels
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Date
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1992
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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, Genetics | Biology, Molecular | Chemistry, Biochemistry
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Abstract
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Maltose fermentation in yeast Saccharomyces strains requires the presence of one or more of five unlinked, structural and functional homologous MAL loci: MAL1, MAL2, MAL3, MAL4, and MAL6. Each locus is a complex locus consisting of three essential maltose fermentation genes: GENEs 1, 2, and 3. GENE 3 encodes the MAL-activator which is required for the inducible transcription of two structural genes: GENE 1 and GENE 2. While GENE 2 was identified to encode maltase, GENE 1 was found to be required for the synthesis of maltose permease, the maltose transporter.;To determine the structure and function of the GENE 1 product, we have sequenced the MAL61 gene, GENE 1 in MAL6 locus. The MAL61 gene contains an open reading frame of 1842 basepairs which encodes the 614 residue putative MAL61 protein. Hydropathy analysis suggests that the secondary structure of the MAL61 protein contains two blocks of six transmembrane domains separated by an approximately 71 residue intracellular region. Significant sequence and structural homology is seen between the MAL61 protein and a family of known sugar transporters including the human glucose transporters.;The cellular localization of MAL61 was determined by analyzing a functional MAL61-lacZ gene fusion product. Our results demonstrated that MAL61 encodes an integral membrane protein.;We elucidated the biochemical and physiological nature of MAL61 by carrying out kinetic studies of maltose uptake in genetically defined Saccharomyces strains. MAL11 and MAL61 were shown to encode an inducible, high-affinity maltose transporter. A low-affinity maltose transporter, which is also detected in maltose-fermenting strains containing MAL1 or MAL6 locus, was found to be expressed constitutively and not to be related to MAL11 or MAL61.;In addition to structural and functional studies, we investigated the glucose-induced inactivation of the maltose transport system in a genetically defined strain carrying the MAL6 locus. We have demonstrated that the MAL61-encoded maltose transporter is subject to glucose-induced inactivation and this inactivation process is distinguishable from glucose repression of the maltose fermentative enzymes including both maltose permease and maltase. We have shown that glucose specifically targets the inactivation of the MAL61 maltose transporter and that a protein synthesis inhibitor, cycloheximide, gives rise to the same affect. The mechanism of the inactivation of maltose transport system is discussed.
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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.
