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dc.contributor.authorYao, Bei
dc.identifier.citationSource: Dissertation Abstracts International, Volume: 52-01, Section: B, page: 8000.;Advisors: Julius Marmur.
dc.description.abstractMaltose utilization in Saccharomyces requires the presence of anyone of the five homologous, unlinked MAL loci. Each locus contains at least three genes: MALT, encoding maltose permease; MALS, encoding maltase; and MALR, encoding a trans-acting regulatory protein, that, upon induction, activates the expression of MALT and MALS. MALT and MALS are divergently transcribed and share a common intergenic (IG) region. The expression of MAL6T and MAL6S in the MAL6 locus is induced by the presence of maltose and repressed by glucose. Here, efforts have been directed in studying the structure of MAL6T, its regulatory mechanism and the encoded maltose permease.;The coding and the divergent promoter regions of MAL6T, were sequenced to obtain insights into the structure of the MAL6T gene and its product. Computer analyses predicted that the encoded maltose permease is membrane-associated and possesses nine transmembrane domains. To detect its subcellular localization and to study its topology, fusions between MAL6T and E. coli lacZ genes were generated. {dollar}\beta{dollar}-galactosidase-fusion reporter activities were determined to be associated with the membrane. A model of maltose permease with multi-transmembrane domains has been proposeed in keeping with the topology studies.;The regulatory mechanism of the MAL6T gene expression was also investigated. A gene fusion of lacZ to the 5{dollar}\sp\prime{dollar} 90 base pairs (bp) of MAL6T expressed {dollar}\beta{dollar}-galactosidase activity under the control of the MAL6T promoter and provided a reliable reporter to monitor wild type and mutant cis-acting regions. Sequential and internal deletions in IG were generated with MAL6T fused in frame to lacZ. The positive and potential negative cis-acting sequences were studied under inducing, non-inducing/non-repressing and repressing conditions. The sequences mediating MAL6T induction were localized between -517 and -609 bp upstream of its ATG translation initiation codon, since its deletion resulted in much reduced maltose induction compared with that of the wild type.;Efforts were directed to determine carbon catabolite repression of MAL6T by glucose is exerted. The carbon sources used contained 2% glucose and 10% maltose. Maltose, at such an elevated concentration, could enter yeast cell without the requirement for maltose permease and therefore, bypass the effect of glucose-induced proteolytic degradation (termed catabolite inactivation) or maltose permease. However, none of the internal deletions in IG derepressed MAL6T expression in the presence of such carbon sources. The results indicate that catabolite repression of MAL6T is not exerted through cis-acting sequences, at least not in the region studied. A likely possibility is that glucose, or a metabolic derivative, represses the interaction of the MAL6R regulatory protein with its cognate promoter; this appear to be the case in the catabolite repression of GAL1-GAL10 expression when glucose appear to affect the interaction of GAL4 with its cognate promoter region.
dc.publisherProQuest Dissertations & Theses
dc.subjectMolecular biology.
dc.titleRegulation of the maltose permease gene expression in Saccharomyces and characterization of the gene product

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