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  • 1
    ISSN: 1432-0983
    Keywords: Saccharomyces cerevisiae ; HEM13 regulation ; Heme and oxygen ; CYP1, ROX1, SSN6, TUP1
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The Saccharomyces cerevisiae HEM13 gene codes for coproporphyrinogen oxidase (CPO), an oxygen-requiring enzyme catalysing the sixth step of heme biosynthesis. Its transcription is increased 40–50-fold in response to oxygen- or heme-deficiency. We have analyzed CPO activity and HEM13 mRNA levels in a set of isogenic strains carrying single or double deletions of the CYP1 (HAP1), ROX1, SSN6, or TUPI genes. The cells were grown in the presence or absence of oxygen and under heme-deficiency (hem1Δ background). Both Rox1p and Cyp1p partially repressed HEM13 in aerobic heme-sufficient cells, probably in an independent manner. In the absence of heme, Cyp1p activated HEM13 and strongly repressed ROX1, allowing de-repression of HEM13. Cyp1p had no effect on HEM13 expression in anaerobic cells. Deletions of SSN6 or TUP1 dramatically de-repressed HEM13 in aerobic cells. A series of deletions in the HEM13 promoter identified at least four regulatory regions that are required for HEM13 regulation. Two regions, containing motifs similar to the Rox1p consensus sequences, act as repression sites under aerobic growth. The two other sites act as activation sequences required for full induction under oxygen- or heme-deficiency. Taken together, these results suggest that induction of HEM13 occurs in part through relief of repression exerted by Rox1p and Cyp1p, and in part by activation mediated partly by Cyp1p under heme-deficiency and by unknown factors under oxygen-deficiency.
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  • 2
    ISSN: 1617-4623
    Keywords: Saccharomyces cerevisiae ; Cell cycle ; Bud site selection ; Guanine exchange factor ; Ras
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Guanine Exchange Factor (GEF) activity for Ras proteins has been associated with a conserved domain in Cdc25p, Sdc25p in Saccharomyces cerevisiae and several other proteins recently found in other eukaryotes. We have assessed the structure-function relationships between three different members of this family in S. cerevisiae, Cdc25p, Sdc25p and Bud5p. Cdc25p controls the Ras pathway, whereas Bud5p controls bud site localization. We demonstrate that the GEF domain of Sdc25p is closely related to that of Cdc25p. We first constructed a thermosensitive allele of SDC25 by specifically altering amino acid positions known to be changed in the cdc25-1 mutation. Secondly, we constructed three chimeric genes from CDC25 and SDC25, the products of which are as active in the Ras pathway as are the wild-type proteins. In contrast, similar chimeras made between CDC25 and BUD5 lead to proteins that are inactive both in the Ras and budding control pathways. This difference in the ability of chimeric proteins to retain activity allows us to define two subclasses of structurally different GEFs: Cdc25p and Sdc25p are Ras-specific GEFs, and Bud5p is a putative GEF for the Rsr1/Bud1 Rap-like protein.
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  • 3
    ISSN: 1617-4623
    Keywords: Saccharomyces cerevisiae ; Actin cytoskeleton ; Budding pattern ; Amphiphysin ; Myosin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The actin cytoskeleton cells is altered in rvs161 mutant yeast, with the defect becoming more pronounced under unfavorable growth conditions, as described for the rvs167 mutant. The cytoskeletal alteration has no apparent effect on invertase secretion and polarized growth. Mutations in RTVS161, just as in RI/S167, lead to a random budding pattern in a/α diploid cells. This behavior is not observed in a/a diploid cells homozygous for the rvs161-1 or rvs167-1 mutations. In addition, sequence comparisons revealed that amphiphysin, a protein first found in synaptic vesicles of chicken and shown to be the autoantigen of Stiff Man syndrome, presents similarity with both Rvs proteins. Furthermore, limited similarities with myosin heavy chain and tropomyosin alpha chain from higher eukaryotic cells allow for the definition of a possible consensus sequence. The finding of related sequences suggests the existence of a function for these proteins that is conserved among eukaryotic organisms.
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  • 4
    ISSN: 1617-4623
    Keywords: Saccharomyces cerevisiae ; Translation ; Splicing ; Paromomycin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The MSS51 gene product has been previously shown to be involved in the splicing of the mitochondrial pre-mRNA of cytochrome oxidase subunit I (COX1). We show here that it is specifically required for the translation of the COX1 mRNA. Furthermore, the paromomycin-resistance mutation (P inf454 supR ) which affects the 15 S mitoribosomal RNA, interferes, directly or indirectly, with the action of the MSS51 gene product. Possible roles of the MSS51 protein on the excision of COX1 introns are discussed.
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  • 5
    ISSN: 1617-4623
    Keywords: Saccharomyces cerevisiae ; Cell cycle ; Proline ; DNA sequencing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We report here the isolation of temperature-sensitive mutants of the yeast Saccharomyces cerevisiae which exhibit cdc phenotypes. The recessive mutations defined four complementation groups, named ore1, ore2, ore3 and ore4. At the non-permissive temperature, strains bearing these mutations arrested in the G1 phase of the cell cycle. The wild-type allele of the gene altered in ore2 mutants was cloned. The nucleotide sequence of a fragment which can complement the mutation showed the presence of an open reading frame capable of encoding a protein with 286 amino acid residues. The deduced amino acid sequence showed 25% identity with that of the Escherichia coli Δ1-pyrroline-5-carboxylate reductase, an enzyme of the pathway for the biosynthesis of proline. The ore2 mutants, correspondingly, were found to be capable of growing at the non-permissive temperature on a synthetic medium supplemented with proline. In addition, the chromosomal location of the gene and its restriction map were compatible with those previously reported for the PRO3 gene which encodes the S. cerevisiae Δ1-pyrroline-5-carboxylate reductase.
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  • 6
    ISSN: 0749-503X
    Keywords: RVS161 gene ; Saccharomyces cerevisiae ; stationary phase entry ; viability loss ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: In yeast, nutrient starvation leads to entry into stationary phase. Mutants that do not respond properly to starvation conditons have been isolated in Saccharomyces cerevisiae. Among them the rvs161 mutant (RVS for Reduced Viability upon Starvation) is sensitive to carbon, nitrogen and sulphur starvation. When these nutrients are depleted in the medium, mutant cells show cellular viability loss with morphological changes. The mutation rvs161-1 is very pleiotropic, and besides the defects in stationary phase entry, the mutant strain presents other alterations: sensitivity to high salt concentrations, hypersensitivity to amino acid analogs, no growth on lactate or acetate medium. The addition of salts or amino acid analogs leads to the same morphological defects observed in starved cells, suggesting that the gene could be implicated mainly in the control of cellular viability. The gene RVS161 was cloned; it codes for a 30,252 daltons protein. No homology was detected with the proteins contained in the databases. Moreover, Southern analysis revealed the presence of other sequences homologous to the RVS161 gene in the yeast genome.
    Additional Material: 6 Ill.
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  • 7
    ISSN: 0749-503X
    Keywords: Chromosome III ; Saccharomyces cerevisiae ; mating type ; HML ; BUD5 ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: This paper reports the DNA sequence of a segment of 9·8 kb of the chromosome III. The sequenced DNA contains the MATα locus. The new sequence of the MATα locus differs from the previously reported sequence by six modifications in the W segment. We have found the same modifications in the HML locus. The corrected sequence contains, in HML, an open reading frame (ORF) of 190 codons which ends at the border between the W segment and the flanking DNA. In the MAT locus, this ORF extends in the flanking DNA up to 538 codons. This ORF corresponds to a gene independently identified as BUD5 (Chant et al., 1991). This gene presents homologies with the exchange factors SDC25 and CDC25. A large ORF of 1399 codons is found on the opposite side of MATα (toward the telomere). This ORF corresponds to a new gene YCR724. Next to this gene is a small ORF, YCR725, of 127 codons. The localization of this fragment on chromosome III, originally supposed to be distal from the MAT locus based on genetic distance, illustrates variation in recombination frequency along the chromosome and suggests the existence of hot spots of recombination between MAT and the THR4 locus.
    Additional Material: 5 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 11 (1995), S. 419-424 
    ISSN: 0749-503X
    Keywords: Saccharomyces cerevisiae ; HEM4 gene ; uroporphyrinogen III synthase ; heme synthesis ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: We have isolated a genomic DNA fragment that complements the yeast temperature-sensitive cyt mutation, causing respiratory deficiency and accumulation of porphyrins (Sugimura et al., 1966). Partial DNA sequencing of the complementing region and search for similarity in the DNA and protein databases revealed that (1) the gene had been previously isolated by complementation of the mutation ts2326 (Langgut et al., 1986; accession number X04694), and (2) it encodes a protein with 18-23% identity to uroporphyrinogen III synthases from different sources. This enzyme catalyses the fourth step in the heme biosynthetic pathway and we named its gene HEM4. A hem4Δ disruption mutation was constructed which had phenotypes identical to the cyt mutation. Biochemical analysis confirmed the absence of uroporphyrinogen III synthase activity in both hem4Δ and cyt mutant strains.
    Additional Material: 3 Ill.
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  • 9
    ISSN: 0749-503X
    Keywords: Saccharomyces cerevisiae ; sterols ; fenpropimorph ; carbon catabolite repression ; nitrogen catabolite repression ; Life Sciences ; Life Sciences (general)
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: We have isolated and characterized a pleiotropic recessive mutation, fen2-1, that causes resistance to fenpropimorph and a low level of ergosterol in Saccharomyces cerevisiae. Ergosterol synthesis in the mutant strain was 5·5-fold slower than in the wild type; however, in vitro assays of the enzymes involved in ergosterol biosynthesis could not account for this low rate in the mutant. The mutant phenotype was expressed only in media exerting both carbon and nitrogen catabolite repression. To our knowledge, this is the first locus in yeast that reveals a concerted regulation between different pathways (carbon and nitrogen catabolite repression and/or general control of amino acid biosynthesis and ergosterol biosynthesis). The yeast gene FEN2 has been isolated and contains an open reading frame (ORF) of 512 codons. This ORF was found to be identical to YCR28C of chromosome III. A possible function of the FEN2 gene product in yeast is discussed.
    Additional Material: 3 Ill.
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  • 10
    ISSN: 0749-503X
    Keywords: Saccharomyces cerevisiae ; plasma membrane purification ; vesicles reconstitution ; K+/H+-exchange ; Life Sciences ; Life Sciences (general)
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: The existence of a K+/H+ transport system in plasma membrane vesicles from Saccharomyces cerevisiae is demonstrated using fluorimetric monitoring of proton fluxes across vesicles (ACMA fluorescence quenching). Plasma membrane vesicles used for this study were obtained by a purification/reconstitution protocol based on differential and discontinuous sucrose gradient centrifugations followed by an octylglucoside dilution/gel filtration procedure. This method produces a high percentage of tightly-sealed inside-out plasma membrane vesicles. In these vesicles, the K+/H+ transport system, which is able to catalyse both K+ influx and efflux, is mainly driven by the K+ transmembrane gradient and can function even if the plasma membrane H+-ATPase is not active. Using the anionic oxonol VI and the cationic DISC2(5) probes, it was shown that a membrane potential is not created during K+ fluxes. Such a dye response argues for the presence of a K+/H+ exchange system in S. cerevisiae plasma membrane and established the non-electrogenic character of the transport. The maximal rate of exchange is obtained at pH 6·8. This reversible transport system presents a high selectivity for K+ among other monovalent cations and a higher affinity for the K+ influx into the vesicles (exit from cells). The possible role of this K+/H+ exchange system in regulation of internal potassium concentration in S. cerevisiae is discussed.
    Additional Material: 11 Ill.
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