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  • 1995-1999  (84)
  • 1940-1944
  • 1900-1904
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  • 11
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Structural genes of phospholipid biosynthesis in the yeast Saccharomyces cerevisiae are activated by the Ino2p/Ino4p transcription factor that binds to ICRE promoter motifs and mediates maximal gene expression in the absence of inositol. We identified the ino80 mutation causing inositol auxotrophy as a result of a defect in ICRE-dependent gene activation. The product of the corresponding wild-type gene INO80 (= YGL150C) shows significant similarity to the Snf2p family of DNA-dependent ATPases. Nevertheless, SNF2 in increased gene dosage did not suppress ino80 mutant phenotypes. Mutation of the Ino80p lysine residue corresponding to the NTP binding site of Snf2p led to a non-functional protein. In ino80 null mutants, gene activation mediated by an ICRE decreased to 16% of the wild-type level. Maximal expression of PHO5, GAL1, CYC1 and ICL1 was also significantly reduced. Thus, Ino80p affects several transcription factors involved in unrelated pathways. As demonstrated by gel filtration, Ino80p is part of a high-molecular-weight complex of more than 1 MDa. Similar to what was found for Snf2p, the Ino80p-containing complex may influence the transcriptional level of several unrelated structural genes by functioning as an ATPase that possibly acts on chromatin.
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  • 12
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The ACS1 gene, encoding one out of two acetyl-CoA synthetase isoenzymes of Saccharomyces cerevisiae, is strictly regulated at the transcriptional level by the carbon source of the medium. While ACS1 is poorly expressed in the presence of a high glucose concentration, a several hundred-fold derepression occurs with ethanol as the sole carbon source or under conditions of sugar limitation. The molecular mechanism responsible for the carbon source control of ACS1 turned out to be highly complex. A carbon source-responsive element (CSRE), previously identified upstream of gluconeogenic structural genes, and a binding site of the alcohol dehydrogenase regulator, Adr1p, together mediate about 80% of the derepressed gene activity. Binding of Adr1p synthesized by Escherichia coli to the ACS1 control region was shown by an electrophoretic mobility shift assay. In addition to these activating elements, two URS1 motifs confer negative control on the ACS1 promoter. The URS1 element was found to be a constitutive repression site, which is most effective from a downstream position with respect to an upstream activation site (UAS). In a mutant lacking the URS1-binding factor, Ume6p, ACS1 expression was partially glucose insensitive. Ume6p must counteract transcription factors that are constitutively active. Site-directed mutagenesis of Abf1p binding sites in the ACS1 promoter significantly reduced gene expression in the ume6 mutant, grown under repressing conditions. Thus, a functional balance of the pleiotropic positive factor Abf1p and the negative factor Ume6p is in part responsible for glucose repression of ACS1. The combined influence of the regulated UAS elements, CSRE and Adr1p binding site, mediates a strong increase in ACS1 expression under derepressing conditions.
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  • 13
    ISSN: 1617-4623
    Keywords: Key wordsSaccharomyces cerevisiae ; Gluconeogenesis ; Malate synthase ; Transcriptional regulation ; MLS1
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The malate synthase gene, MLS1, of the yeast Saccharomyces cerevisiae is transcriptionally regulated by the carbon source in the growth medium. A MLS1-lacZ fusion gene, expressed at a basal level in the presence of 2% glucose, is derepressed more than 100-fold under conditions of sugar limitation. No evidence for MLS1 induction by oleic acid was found. By deletion analysis of the MLS1 control region, we identified two sites, UAS1 and UAS2, as important for efficient derepression of the gene. Both sites contain sequences that resemble the previously characterized carbon source-responsive element (CSRE) found in the promoter of the isocitrate lyase gene ICL1. Indeed, UAS1 and UAS2 in the MLS1 upstream region turn out to be functional CSRE sequence variants. This finding allowed us to define a modified version of the CSRE consensus sequence (CCRTYSRNCCG). Protein binding to UAS1MLS1 was observed with extracts from derepressed but not from repressed cells, and could be competed for by an excess of the unlabelled CSRE(ICL1) sequence. No competition was observed with a mutated CSRE variant. Site-directed mutagenesis of both CSREs in the MLS1 promoter reduced gene activation under derepressing conditions to 20% of the wild-type level. The same decrease was observed with the wild-type MLS1 promoter in a cat8 mutant, lacking an activator of CSRE-dependent transcription. The CSRE/Cat8p-independent activation of MLS1 is mediated by constitutive UAS elements. The pleiotropic transcription factor Abf1p, which binds to the MLS1 upstream region, may contribute to constitutive activation. Thus, in order to ensure the severe glucose repression of MLS1 observed, repressor elements that respond to the carbon source must counteract constitutive activation. In summary, ICL1 and MLS1 share common cis-acting elements, although a distinct mechanism of carbon source control also contributes to MLS1 regulation.
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  • 14
    Electronic Resource
    Electronic Resource
    Springer
    Sexual plant reproduction 10 (1997), S. 101-106 
    ISSN: 1432-2145
    Keywords: Key words Pollen ; Pollen competition ; Pollen performance ; Microgametophyte
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  We examined the influence of pollen competitive environment on pollen performance in Mirabilis jalapa. We used the number of pollen grains and the number of pollen tubes per pistil as measures of pollen competition. Pollen germination, pollen tube penetration into the style, and pollen tube growth rates were used as measures of pollen performance. All three measures of pollen performance were affected by the competitive environment. Pollen germination was greatest at intermediate pollen load sizes. The percentage of germinated pollen grains that penetrated the stigma and grew into the style decreased with pollen load size. Pollen tube growth rate in the style was greater and more variable with larger numbers of pollen tubes in the style. Controlling for the degree of selection at the stigma indicated that pollen-pollen or pollen-style interactions were the likely causes of increased growth rates.
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  • 15
    Electronic Resource
    Electronic Resource
    Springer
    Archive of applied mechanics 69 (1999), S. 765-784 
    ISSN: 1432-0681
    Keywords: Key words Finite elements, statistical equivalent linearization, component-mode synthesis, complex modal analysis, random eigenvalue problem, hysteresis, damping
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary This paper focuses on the stochastic dynamic response of structures modeled by finite elements with a relatively large number of degrees of freedom. FE models with nonlinearities and uncertain (stochastic) system properties are discussed. It is shown that component mode synthesis can be used most advantageously to solve the issue of computational efficiency and feasibility. The stochastic response due to stochastic loading of large FE models with nonlinear elements is determined by statistical equivalent linearization (EQL). The developed component-mode synthesis allows to determine the complex modal properties of arbitrary large linearized finite element models. Nonsymmetric structural matrices, as a result of the EQL, and filters for modeling of filtered white noise can be treated by the suggested approach. Since the efficiency of the procedure is nearly independent of the number of degrees-of-freedom (DOF) involved, statistical equivalent linearization becomes applicable for arbitrary detailed FE models. Furthermore, the dynamic response of FE models with uncertain or stochastic system properties is discussed. In this case, Monte Carlo simulation is suggested as the most appropriate approach for FE models. The paper focuses on the random eigenvalue problem for large FE systems as the computationally most demanding part of the dynamic analysis. Component-mode synthesis is used to provide in an efficient manner all the eigenvalue solutions of the FE system needed by the Monte Carlo simulation.
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  • 16
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 40 (1904), S. 385-399 
    ISSN: 0863-1778
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
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  • 17
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical methods of operations research 46 (1997), S. 287-307 
    ISSN: 1432-5217
    Keywords: Reliability-based optimization ; structural reliability ; cost function ; nonlinear programming ; Monte Carlo simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract A method to carry out a Reliability-Based Optimization (RBO) of especially nonlinear structural systems is introduced. Statistical uncertainties involving both structural and loading properties are considered. The concept is based on the separation of structural reliability analyses and the optimization procedures. Two approaches are discussed, depending on the interaction of reliability analysis and mathematical programming and the way of representation of the limit state functions (LSF) of the structure. As, for cases of practical significance, the LSF is known only pointwise it is approximated by Response Surfaces (RS). For the response calculations Finite Element (FE) procedures are utilized. Failure probabilities are determined by applying variance reducing Monte Carlo simulation (MCS) techniques such as Importance Sampling (IS). Following the reliability analysis, the optimization procedure is controlled by the NLPQL algorithm. A numerical example in terms of a template ocean platform exemplifies the procedures.
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  • 18
    ISSN: 1617-4623
    Keywords: Prolidase ; Metalloprotease ; Lactobacillus delbrueckii subsp. lactis ; Nucleotide sequence analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract From a genomic library of Lactobacillus delbrueckii subsp. lactis (DSM7290) DNA, in the low-copy-number vector pLG339, a recombinant clone was selected, which complemented a mutation in the prolidase gene (pepQ) of Escherichia coli UK173. Nucleotide sequence analysis revealed an open reading frame of 1104 nucleotides corresponding to a protein of 368 amino acids with a calculated pI of 4.64 and a molecular mass of 41087 Da. The start site of pepQ transcription was determined by primer extension analysis with mRNA prepared from L. delbrueckii. Based on homology of the gene product to various peptidases and on the substrate specificity determined, the peptidase was designated PepQ. The influence of various protease inhibitors and cations on peptidase activity indicated that PepQ is a metalloprotease. The absence of a membrane-spanning domain and a signal peptide sequence argues for a cytoplasmic localization of the enzyme.
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  • 19
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 24 (1997), S. 875-892 
    ISSN: 0271-2091
    Keywords: adaptive parallel multigrid method ; local refinement criteria ; incompressible Navier-Stokes equations ; hole pressure problem ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In this paper an adaptive parallel multigrid method and an application example for the 2D incompressible Navier-Stokes equations are described. The strategy of the adaptivity in the sense of local grid refinement in the multigrid context is the multilevel adaptive technique (MLAT) suggested by Brandt. The parallelization of this method on scalable parallel systems is based on the portable communication library CLIC and the message-passing standards: PARMACS, PVM and MPI. The specific problem considered in this work is a two-dimensional hole pressure problem in which a Poiseuille channel flow is disturbed by a cavity on one side of the channel. Near geometric singularities a very fine grid is needed for obtaining an accurate solution of the pressure value. Two important issues of the efficiency of adaptive parallel multigrid algorithms, namely the data redistribution strategy and the refinement criterion, are discussed here. For approximate dynamic load balancing, new data in the adaptive steps are redistributed into distributed memories in different processors of the parallel system by block remapping. Among several refinement criteria tested in this work, the most suitable one for the specific problem is that based on finite-element residuals from the point of view of self-adaptivity and computational efficiency, since it is a kind of error indicator and can stop refinement algorithms in a natural way for a given tolerance. Comparisons between different global grids without and with local refinement have shown the advantages of the self-adaptive technique, as this can save computer memory and speed up the computing time several times without impairing the numerical accuracy. © 1997 By John Wiley & Sons, Ltd. Int. J. Numer. Methods Fluids 24, 875-892, 1997.
    Additional Material: 13 Ill.
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  • 20
    ISSN: 0935-9648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Additional Material: 4 Ill.
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