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  • Articles  (43)
  • 1995-1999  (22)
  • 1990-1994  (21)
  • Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics  (21)
  • Medicine  (20)
  • Mathematics  (2)
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  • Articles  (43)
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  • 1
    ISSN: 1520-5002
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 2
    ISSN: 1520-5002
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 3
    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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  • 4
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: In the yeast Saccharomyces cerevisiae, growth with a non-fermentable carbon source requires co-ordinate transcriptional activation of gluconeogenic structural genes by an upstream activation site (UAS) element, designated CSRE (carbon source-responsive element). The zinc cluster protein encoded by CAT8 is necessary for transcriptional derepression mediated by a CSRE. Expression of CAT8 as well as transcriptional activation by Cat8p is regulated by the carbon source, requiring a functional Cat1p (= Snf1p) protein kinase. The importance of both regulatory levels was investigated by construction of CAT8 variants with a constitutive transcriptional activation domain (INO2TAD) and/or a carbon source-independent promoter (MET25 ). Whereas a reporter gene driven by a CSRE-dependent synthetic minimal promoter showed a 40-fold derepression with wild-type CAT8, an almost constitutive expression was found with a MET25–CAT8–INO2TAD fusion construct due to a dramatically increased gene activation under conditions of glucose repression. Similar results were obtained with the mRNA of the isocitrate lyase gene ICL1 and at the level of ICL enzyme activity. Taking advantage of a Cat8p size variant, we demonstrate its binding to the CSRE. Our data show that carbon source-dependent transcriptional activation by Cat8p is the most important mechanism affecting the regulated expression of gluconeogenic structural genes.
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  • 5
    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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  • 6
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The higher plant Arabidopsis thaliana (Arabidopsis) is an important model for identifying plant genes and determining their function. To assist biological investigations and to define chromosome structure, a coordinated effort to sequence the Arabidopsis genome was initiated in late 1996. Here we ...
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS immunology and medical microbiology 20 (1998), S. 0 
    ISSN: 1574-695X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Macrophage cells play a central role during infection with Listeria monocytogenes by both providing a major habitat for bacterial multiplication and presenting bacterial antigens to the immune system. In this study, we investigated the influence of L. monocytogenes infection on the expression of MHC class I and class II genes in two murine macrophage cell lines. Steady-state levels of I-Aβ chain mRNA were decreased in both resting J774A.1 and P388D1 macrophages infected with L. monocytogenes whereas reduction of H-2K mRNA was only observed in P388D1 cells. In addition, L. monocytogenes suppressed induction of MHC class I and class II mRNAs in response to γ-interferon as well as the maintenance of the induced state in activated P388D1 macrophages. Exposure to the non-pathogenic species L. innocua or a deletion mutant of L. monocytogenes, which lacks the lecithinase operon, did not cause a reduction in H-2K and I-Aβ mRNA levels nor suppress expression of Ia antigens. Inhibition of MHC gene expression may represent an important part of the cross-talk between L. monocytogenes and the macrophage that probably influences the efficiency of a T cell-mediated immune response and thus the outcome of a listerial infection.
    Type of Medium: Electronic Resource
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  • 8
    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.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 26 (1991), S. 3287-3291 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract It is well known that the microstructure of metal-matrix composite materials is significantly different from that of the unreinforced matrix. Heat treatments which optimized strength values in the matrix therefore, no longer do so in the composite. It is thus beneficial to find these variations in the heat treatment process, and to pinpoint the microstructural mechanisms responsible. It is known that, in addition to a higher dislocation density, the composite also has a very fine grain size and many whisker interfacial nucleation sites. This study has found that the time required for solutionizing appears to be much shorter in the composite primarily due to the very small grain size. It was also observed that artificial ageing was not very effective in the composite since the precipitates nucleated and grew on the whisker interfaces, therefore, only natural ageing was necessary to achieve peak tensile and yield strengths.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 29 (1994), S. 239-249 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract An interesting cubic-shaped precipitate was observed in the matrix of a squeeze-cast Al-4.3 wt % Cu-2.0 wt % Mg/SiC composite which was heat-treated to a T7 condition. Although this phase had been observed by a few investigators in the past, it had never been examined in detail until now. This cubic phase generally had an edge length ranging from 30 to 50 nm and existed in volume fractions as high as 3.8%. Theoretical strengthening models predicted this phase to have good potential for precipitate strengthening. In addition, the cubic phase exhibited a low rate of coarsening at temperatures as high as 250 °C; apparently due to its low interfacial energy. Consequently, this cubic precipitate shows potential for increasing the useful temperature range of aluminium alloys and composites and could be of great importance to the aerospace and automotive industries.
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