Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.2.1.20 (alpha-glucosidase)
4,237 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The presence of any one of the five unlinked MAL loci (MAL1, MAL2, MAL3, MAL4 and MAL6) confers the ability to ferment maltose on the yeast Saccharomyces cerevisiae. Each locus is composed of three genes encoding maltose permease, alpha-glucosidase and MAL activator. Chromosomal DNA of seven representative baking strains has been separated by pulse-field gel electrophoresis and probed with three genes in MAL6 locus. The DNA bands to which all of the three MAL-derived probes simultaneously hybridized were chromosome VII carrying MAL1 in all of the strains tested, chromosome XI carrying MAL4 in six strains, chromosome III carrying MAL2 in three strains and chromosomes II and VIII carrying MAL3 and MAL6, respectively, in the one strain. The number of MAL loci in baking strains was comparable to those of brewing strains.
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PMID:Detection of maltose fermentation genes in the baking yeast strains of Saccharomyces cerevisiae. 898 1

In Saccharomyces cerevisiae maltose utilization requires a functional MAL locus, each composed of three genes: MALR (gene 3) encoding a regulatory protein, MALT (gene 1) encoding maltose permease and MALS (gene 2) encoding maltase. We show that constitutive activation of the RAS/protein kinase A pathway severely reduces growth of MAL1 strains on maltose. This may be a consequence of reduction in MALT mRNA, reduced Vmax and increased catabolite inactivation of the MALT-encoded maltose transporter in the MAL1 strain. Mutations in the GGS1/TPS1 gene, which restricts glucose influx and possibly affects signalling, relieve carbon catabolite repression on both maltase and maltose permease and reduce maltose permease inactivation.
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PMID:Regulation of maltose utilization in Saccharomyces cerevisiae by genes of the RAS/protein kinase A pathway. 903 5

We have studied four novel MAL promoters isolated from a single strain of bakers' yeast. Within these promoters we have identified up to five tandem 147 bp repeats located between the MAL UAS region and the MALT TATA box. These repeats strongly reduce MALT (maltose permease) gene expression but only weakly reduce MALS (maltase) gene expression. Insertion of the 147 bp elements into the heterologous CYC1 promoter reduced expression when located between the CYC1 UAS and the TATA box, but not when located upstream of the UAS. We propose that these naturally occurring repeats have evolved as a mechanism to lower the level of MALT expression relative of MALS expression, thus avoiding possible toxic effects associated with over-expression from multiple copies of the permease gene.
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PMID:Tandemly repeated 147 bp elements cause structural and functional variation in divergent MAL promoters of Saccharomyces cerevisiae. 930 Oct 20

To utilise maltose as a carbon source Saccharomyces cerevisiae needs one or more functional MAL loci that contain the MALx1 gene encoding maltose permease, MALx2 encoding maltase, and MALx3 encoding a transcriptional activator. Maltose causes a rapid MALx3-dependent induction of MAL gene transcription, and glucose represses this activation via Mig1p. A MALx3 gene conveying high MAL gene expression in the absence of maltose in a malx3 laboratory mutant strain has been isolated from baker's yeast. The construction of hybrid genes between the isolated gene and a highly regulated MALx3 gene showed that constitutivity was the result of multiple amino-acid alterations throughout the structural gene. The combined effect of these amino-acid alterations was shown to be stronger than the sum of their individual effects on constitutivity. Analysis in glucose-repressed conditions confirmed that increased MALx3 transcript levels increased the glucose insensitivity of MAL gene expression but did not affect constitutivity. Analysis of four mutations between aa 343 and 375, lying within a proposed negative regulatory domain, showed that the single mutation of Leu343Phe increased the glucose insensitivity of MAL gene expression by 30-fold. These results demonstrate that not only Mig1p modulation of MALx3 expression, but also the MALx3 protein structure, is involved in the glucose-insensitive expression of the MAL genes.
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PMID:Leu343Phe substitution in the Malx3 protein of Saccharomyces cerevisiae increases the constitutivity and glucose insensitivity of MAL gene expression. 1036 55

Some industrial strains of Saccharomyces cerevisiae are unable to maintain high rates of fermentation during transition from catabolism of hexoses to maltose. This phenomenon, termed 'maltose lag', presents problems for the baking, brewing and distilling industries, which rely on yeast catabolism of mixtures of hexoses and maltose. Maltose utilisation requires the presence of maltose permease and alpha-glucosidase (maltase), encoded by MAL genes. Synthesis of these is induced by maltose and repressed by glucose. One strain of baker's yeast used in this work exhibited a marked maltose lag, whereas a second strain exhibited a shorter lag during conversion from hexose to maltose metabolism. The extent of the lag was linked to the levels of maltose permease and maltase in cells at the time of inoculation into mixed sugar medium. This view is supported by results showing that pulsing yeast with maltose to induce expression of MAL genes prior to inoculation into mixed sugar medium, enhanced sugar fermentation. Maltose pulsing of yeasts could therefore be useful for enhancing some fermentations relevant to baking and other yeast industries.
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PMID:Enhancement of maltose utilisation by Saccharomyces cerevisiae in medium containing fermentable hexoses. 1045 90

Maltose transport and maltase activities were inactivated during sporulation of a MAL constitutive yeast strain harboring different MAL loci. Both activities were reduced to almost zero after 5 h of incubation in sporulation medium. The inactivation of maltase and maltose permease seems to be related to optimal sporulation conditions such as a suitable supply of oxygen and cell concentration in the sporulating cultures, and occurs in the fully derepressed conditions of incubation in the sporulation acetate medium. The inactivation of maltase and maltose permease under sporulation conditions in MAL constitutive strains suggests an alternative mechanism for the regulation of the MAL gene expression during the sporulation process.
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PMID:Inactivation of maltose permease and maltase in sporulating Saccharomyces cerevisiae. 1077 76

The Saccharomyces MAL-activator regulates the maltose-inducible expression of the MAL structural genes encoding maltose permease and maltase. Constitutive MAL-activator mutant alleles of two types were identified. The first were truncation mutations deleting C-terminal residues 283-470 and the second contained a large number of alterations compared to inducible alleles scattered throughout the C-terminal 200 residues. We used site-directed in vitro mutagenesis of the inducible MAL63 and MAL63/23 genes to identify the residues responsible for the negative regulatory function of the C-terminal domain. Intragenic suppressors that restored the inducible phenotype to the constitutive mutants were identified at closely linked and more distant sites within the MAL-activator protein. MAL63/mal64 fusions of the truncated mutants suggest that residues in the N-terminal 100 residues containing the DNA-binding domain also modulate basal expression. Moreover, a transcription activator protein consisting of LexA(1-87)-Gal4(768-881)-Mal63(200-470) allowed constitutive reporter gene expression, suggesting that the C-terminal regulatory domain is not sufficient for maltose-inducible control of this heterologous activation domain. These results suggest that complex and very specific intramolecular protein-protein interactions regulate the MAL-activator.
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PMID:Alterations in the Saccharomyces MAL-activator cause constitutivity but can be suppressed by intragenic mutations. 1119 Dec 6

Induction of the Saccharomyces MAL structural genes encoding maltose permease and maltase requires the MAL activator, a DNA-binding transcription activator. Genetic analysis of MAL activator mutations suggested that protein folding and stability play an important role in MAL activator regulation and led us to explore the role of the Hsp90 molecular chaperone complex in the regulation of the MAL activator. Strains carrying mutations in genes encoding components of the Hsp90 chaperone complex, hsc82 Delta hsp82-T101I and hsc82 Delta cpr7 Delta, are defective for maltase induction and exhibit significantly reduced growth rates on media containing a limiting concentration of maltose (0.05%). This growth defect is suppressed by providing maltose in excess. Using epitope-tagged alleles of the MAL63 MAL activator, we showed that Mal63p levels are drastically reduced following depletion of cellular Hsp90. Overexpression ( approximately 3-fold) of Mal63p in the hsc82 Delta hsp82-T101I and hsc82 Delta cpr7 Delta strains suppresses their Mal- growth phenotype, suggesting that Mal63p levels are limiting for maltose utilization in strains with abrogated Hsp90 activity. Consistent with this, the half-life of Mal63p is significantly shorter in the hsc82 Delta cpr7 Delta strain (reduced about 6-fold) and modestly affected in the Hsp90-ts strain (reduced about 2-fold). Most importantly, triple hemagglutinin-tagged Mal63p protein is found in association with Hsp90 as demonstrated by co-immunoprecipitation. Taken together, these results identify the inducible MAL activator as a client protein of the Hsp90 molecular chaperone complex and point to a critical role for chaperone function in alternate carbon source utilization in Saccharomyces cerevisiae.
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PMID:The Hsp90 molecular chaperone complex regulates maltose induction and stability of the Saccharomyces MAL gene transcription activator Mal63p. 1450 Jul 8

The MAL-activator genes of Saccharomyces cerevisiae encode regulatory proteins required for the expression of the structural genes encoding maltose permease and maltase. Residues within the C-terminal region of the Mal63 protein required for negative regulation were previously identified. Evidence suggested that the C-terminal domain is also involved in positive regulatory functions, such as inducer responsiveness and transactivation in the context of a full-length protein. Charged-cluster to alanine scanning mutagenesis of the regulatory domain of MAL63 and the constitutive MAL43-C were undertaken to identify distinct regions within Mal63p involved in positive functions and to define their roles in induction. Mutations that affect the ability to activate transcription in the inducible MAL63 but have no effect in the constitutive MAL43-C define regions that function in induction. Those that affect both the inducible and constitutive alleles define regions involved in activation more generally. Mutations in MAL63 fell into three classes, those that have little or no impact on activity, those that decrease activity, and those that enhance function. Mutations from these classes mapped to distinct regions of the protein, identifying a region of approximately 90 residues (residues 331-423) involved in maltose sensing and an approximately 50-residue region at the extreme C-terminus (residues 420-470) required for activation, such as the formation and/or maintenance of an active state. These studies support a model for MAL-activator function which involves complex protein-protein interactions and overlapping negative and positive regulatory regions.
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PMID:Clustered-charge to alanine scanning mutagenesis of the Mal63 MAL-activator C-terminal regulatory domain. 1450 2

Hansenula polymorpha is an exception among methylotrophic yeasts because it can grow on the disaccharides maltose and sucrose. We disrupted the maltase gene (HPMAL1) in H. polymorpha 201 using homologous recombination. Resulting disruptants HP201HPMAL1Delta failed to grow on maltose and sucrose, showing that maltase is essential for the growth of H. polymorpha on both disaccharides. Expression of HPMAL1 in HP201HPMAL1Delta from the truncated variants of the promoter enabled us to define the 5'-upstream region as sufficient for the induction of maltase by disaccharides and its repression by glucose. Expression of the Saccharomyces cerevisiae maltase gene MAL62 was induced by maltose and sucrose, and repressed by glucose if expressed in HP201HPMAL1Delta from its own promoter. Similarly, the HPMAL1 promoter was recognized and correctly regulated by the carbon source in a S. cerevisiae maltase-negative mutant 100-1B. Therefore we suggest that the transcriptional regulators of S. cerevisiae MAL genes (MAL activator and Mig1 repressor) can affect the expression of the H. polymorpha maltase gene, and that homologues of these proteins may exist in H. polymorpha. Using the HPMAL1 gene as a reporter in a H. polymorpha maltase disruption mutant it was shown that the strength of the HPMAL1 promoter if induced by sucrose is quite comparable to the strength of the H. polymorpha alcohol oxidase promoter under conditions of methanol induction, revealing the biotechnological potential of the HPMAL1 promoter.
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PMID:Regulation of the Hansenula polymorpha maltase gene promoter in H. polymorpha and Saccharomyces cerevisiae1. 1461 81


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