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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Molecular genetics and genomics 154 (1977), S. 23-30 
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In Saccharomyces cerevisiae, the products of eleven different genes are needed for a functional sulfate assimilation pathway. Only five enzymatic steps are known in this pathway. The study of the gene-enzyme relationships has shown that the enzymes catalysing two of these steps are probably heteropolymeric. Moreover, mutations in three unlinked genes lead to multiple enzymatic losses. Different hypotheses are made to account for these results.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1617-4623
    Keywords: Recombinant DNA ; Methionine metabolism ; Negative control ; Regulatory regions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In Saccharomyces cerevisiae, the expression of several genes implicated in methionine biosynthesis is coregulated by a specific negative control. To elucidate the molecular basis of this regulation, we have cloned two of these genes, MET3 and MET25. The sequence of MET25 has already been determined (Kerjan et al. 1986). Here, we report the nucleotide sequence of the MET3 gene along with its 5′ and 3′ flanking regions. Plasmids bearing different deletions upstream of the transcribed region of MET3 were constructed. They were introduced into yeast cells and tested for their ability to complement met3 mutations and to respond to regulation by exogenous methionine. The regulatory region was located within a 100 bp region. The sequence of this regulatory region was compared with that of MET25. A short common sequence which occurs 250–280 bp upstream of the translation initiation codon of the gene was found. This sequence is a good candidate for the cis-acting regulatory element.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Molecular genetics and genomics 217 (1989), S. 149-154 
    ISSN: 1617-4623
    Keywords: Saccharomyces cerevisiae ; HOM2 gene ; Aspartic semi-aldehyde ; General control
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In Saccharomyces cerevisiae the HOM2 gene encodes aspartic semi-aldehyde dehydrogenase (ASA DH). The synthesis of this enzyme had been shown to be derepressed by growth in the presence of high concentrations of methionine. In the present work we have cloned and sequenced the HOM2 gene and found that the promoter region of this gene bears one copy of the consensus sequence for general control of amino acid synthesis. This prompted us to study the regulation of the expression of the HOM2 gene. We have found that ASA DH is the first reported enzyme of the related threonine and methionine pathway to be regulated by the general control of amino acid synthesis.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Mutants requiring S-adenosyl methionine (SAM) for growth have been selected in Saccharomyces cerevisiae. Two classes of mutants have been found. One class corresponds to the simultaneous occurrence of mutations at two unlinked loci SAM1 and SAM2 and presents a strict SAM requirement for growth on any medium. The second class corresponds to special single mutations in the gene SAM2 which lead to a residual growth on minimal medium but to normal growth on SAM supplemented medium or on a complex medium like YPGA not containing any SAM. These genetic data can be taken as an indication that Saccharomyces cerevisiae possesses two isoenzymatic methionine adenosyl transferases (MAT). In addition, SAM1 and SAM2 loci have been identified respectively with the ETH-10 and ETH2 loci previously described. Biochemical evidences corroborate the genetic results. Two MAT activities can be dissociated in a wild type extract (MATI and MATII) by DEAE cellulose chromatography. Mutations at the SAM1 locus lead to the absence or to the modification of MATII whereas mutations at the SAM2 locus lead to the absence or to the modification of MATI. Moreover, some of our results seem to show that MATI and MATII are associated in vivo.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Molecular genetics and genomics 182 (1981), S. 65-69 
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In Saccharomyces cerevisiae either of the two genes SAM1 and SAM2 is able to produce a functional methionine adenosyl transferase (MATI and MATII). In a wild-type strain, MATI and MATII are present in dimeric forms: MATI-MATI, MATII-MATII and perhaps MATI-MATII. A hypothesis is presented to explain the possible role of these different forms of methionine adenosyl transferase in S. cerevisiae.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1617-4623
    Keywords: Sulfur metabolism ; Vacuolar biogenesis ; Transcription
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In order to isolate new mutations impairing transcriptional regulation of sulfur metabolism inSaccharomyces cerevisiae, we used a potent genetic screen based on a gene fusion expressing XylE (fromPseudomonas putida) under the control of the promoter region ofMET25. This selection yielded strains mutated in various different genes. We describe in this paper the properties of one of them,MET27. Mutation or disruption ofMET27 leads to a methionine requirement and affects S-adenosylmethionine (AdoMet)-mediated transcriptional control of genes involved in sulfur metabolism. The cloning and sequencing ofMET27 showed that it is identical toVPS33. Disruptions or mutations of geneVPS33 are well known to impair the biogenesis and inheritance of the vacuolar compartment. However, the methionine requirement ofvps33 mutants has not been reported previously. We show here, moreover, that other vps mutants of class C (no apparent vacuoles) also require methionine for growth. Northern blotting experiments revealed that themet27-1 mutation delayed derepression of the transcription of genes involved in sulfur metabolism. By contrast, this delay was not observed in amet27 disrupted strain. Physiological and morphological analyses ofmet27-1 andmet27 disrupted strains showed that these results could be explained by alterations in the ability of the vacuole to transport or store AdoMet, the physiological effector of the transcriptional regulation of sulfur metabolism.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1617-4623
    Keywords: Methionine metabolism ; Gene complementation ; MET25 gene ; Sulphydrylase ; Saccharomyces cerevisiae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We cloned the MET17 gene of Saccharomyces cerevisiae by functional complementation after transformation of a yeast met17 mutant. Restriction mapping and nucleotide sequencing of the MET17 clones revealed that these were from the same genomic region as clones isolated previously and shown to contain the MET25 gene encoding the enzyme O-acetylhomoserine, O-acetylserine sulphydrylase (OAH-OAS sulphydrylase). Transformation studies with MET25 clones showed that the MET17 and MET25 functions were both endoced in a single transcription unit. We conclude that met17 and met25 are both mutations in the structural gene for the OAH-OAS sulphydrylase subunit and that each affects a different fuctional domain of the enzyme allowing subunit complementation in the met17xmet25 diploid. Enzyme assays indicated that the diploid, although not requiring methionine, had a low OAH-OAS sulphydrylase activity (10% of wild type). This is consistent with MET17 and MET25 being the same gene. We found that both met17 and met25 mutants were devoid of 3′ phospho-adenosine 5′ phospho-sulphite (PAPS) reductase activity and that this activity was fully restored in the met17xmet25 diploid. The possible interactions between OAH-OAS sulphydrylase and PAPS reductase are discussed.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Molecular genetics and genomics 200 (1985), S. 407-414 
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The MET25 gene of Saccharomyces cerevisiae was cloned by functional complementation after transformation of a yeast met25 mutant. Subcloning of the DNA fragment bearing MET25 located the gene on a 2.3 kb region. The gene was formally identified by integration at the chromosomal MET25 locus. The cloned MET25 gene was used as a probe to measure the MET25 messenger RNA in a wild-type strain grown under conditions which promoted or failed to promote repression of MET25 expression. It was found that, under repression conditions, MET25 messenger RNA was reduced tenfold when compared with non-repression conditions. This suggests that the expression of MET25 is regulated transcriptionally. The direction of transcription, the size of the transcript and the position of the transcribed part of the gene were determined. Deletion mapping of the regulatory region was carried out. Deleted plasmids were introduced back into yeast cells and tested for their ability to complement met25 mutations and to promote regulation of expression of the MET25 gene by exogenous methionine. By this method the regulatory region was found to be confined to a 130 bp region.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Molecular genetics and genomics 226 (1991), S. 224-232 
    ISSN: 1617-4623
    Keywords: Saccharomyces cerevisiae ; SAM1 and SAM2 genes ; Transcription
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary S-adenosyl-l-methionine (AdoMet) is synthesized by transfer of the adenosyl moiety of ATP to the sulfur atom of methionine. This reaction is catalysed by AdoMet synthetase. In all eukaryotic organisms studied so far, multiple forms of AdoMet synthetases have been reported and from their recent study, it appears that AdoMet synthetase is an exceptionally well conserved enzyme through evolution. In Saccharomyces cerevisiae, we have demonstrated the existence of two AdoMet synthetases encoded by genes SAM1 and SAM2. Yeast, which is able to concentrate exogenously added AdoMet, is thus a particularly useful biological system to understand the role and the physiological significance of the preservation of two almost identical AdoMet synthetases. The analysis of the expression of the two SAM genes in different genetic backgrounds during growth under different conditions shows that the expression of SAM1 and SAM2 is regulated differently. The regulation of SAM1 expression is identical to that of other genes implicated in AdoMet metabolism, where as SAM2 shows a specific pattern of regulation. A careful analysis of the expression of the two genes and of the variations in the methionine and AdoMet intracellular pools during the growth of different strains lead us to postulate the existence of two different AdoMet pools, each one suppplied by a different AdoMet synthetase but in equilibrium with each other. This could be a means of storing AdoMet whenever this metabolite is overproduced, thus avoiding the degradation of a metabolite the synthesis of which is energetically expensive.
    Type of Medium: Electronic Resource
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