Multiple mechanisms mediate glucose regulation of MAL gene expression in Saccharomyces cerevisiae.
Item
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Title
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Multiple mechanisms mediate glucose regulation of MAL gene expression in Saccharomyces cerevisiae.
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Identifier
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AAI9807941
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identifier
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9807941
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Creator
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Hu, Zhen.
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Contributor
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Adviser: Corinne A. Michels
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Date
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1997
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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, Genetics | Chemistry, Biochemistry
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Abstract
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Maltose fermentation in Saccharomyces cerevisiae requires at least one of five unlinked MAL loci. Each MAL locus is a complex of three genes: Gene 1 encodes maltose permease; Gene 2 encodes maltase; Gene 3 encodes the MAL-activator. Expression of the MAL structural genes is induced by maltose and repressed by glucose. Maltose induction is mediated by a MAL-activator and requires the presence of a functional maltose permease gene. Two MAL structural genes share a bidirectional promoter which contains the upstream activating sequence, the UAS{dollar}\rm\sb{lcub}MAL{rcub}.{dollar} We undertook the present study to analyze the mechanisms of glucose repression of MAL gene expression.;MIG1 encodes a zinc-finger DNA binding protein which represses the transcription of SUC2 and GAL genes in response to glucose. Mig1p is a downstream component of the Snf1p kinase signal transduction pathway that mediates glucose repression. We demonstrate that Mig1p binds to two sites located in the MAL61-MAL62 intergenic region and represses the transcription of these two MAL structural genes in the presence of glucose. Mig1p also binds to the promoter of MAL63 and represses the transcription of this MAL-activator gene. Studies using constitutive MAL-activator alleles reveal that glucose inhibits the MAL-activator-mediated maltose induction by mechanisms that are independent of Mig1p.;HXK2 encodes a glucose phosphorylating enzyme, hexokinase PII. We found that Hxk2p mediates glucose repression of maltase expression including those repression effects that are independent of Mig1p. HXK1 encoding hexokinase PI, in hxk2 background, is able to play some of the roles of Hxk2p in transmitting/generating glucose repression signal acting on the MAL promoters.;We show that overexpression of the MAL-activator is not sufficient to relieve glucose inhibition of maltose induction. Moreover, elimination of inducer exclusion does not alleviate glucose inhibition of the function of the overexpressed MAL-activator. These results suggest that glucose inhibits maltose induction by affecting the induction process and/or events required for induction (induction-dependent mechanism). This mechanism requires REG1 (a regulatory subunit of protein phosphatase type-1), GRR1 (a putative ubiquitin protein ligase), as well as HXK2, but does not appear to involve RGT1 (a repressor of hexose transporter genes) and RGT2 (a high-glucose sensor).
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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.
