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  • 1
    ISSN: 1432-0983
    Keywords: Key words Transcriptional regulation ; Phospholipid biosynthesis ; Saccharomyces cerevisiae ; INO2
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Expression of structural genes of phospholipid biosynthesis in yeast is mediated by the inositol/choline-responsive element (ICRE). ICRE-dependent gene activation, requiring the regulatory genes INO2 and INO4, is repressed in the presence of the phospholipid precursors inositol and choline. INO2 and, to a less extent, INO4 are positively autoregulated by functional ICRE sequences in the respective upstream regions. However, an INO2 allele devoid of its ICRE functionally complemented an ino2 mutation and completely restored inositol/choline regulation of Ino2p-dependent reporter genes. Low-level expression of INO2 and INO4 genes, each under control of the heterologous MET25 promoter, did not alter the regulatory pattern of target genes. Thus, upstream regions of INO2 and INO4 are not crucial for transcriptional control of ICRE-dependent genes by inositol and choline. Interestingly, over-expression of INO2, but not of INO4, counteracted repression by phospholipid precursors. Possibly, a functional antagonism between INO2 and a negative regulator is the key event responsible for repression or de-repression.
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  • 2
    ISSN: 1432-0983
    Keywords: Saccharomyces cerevisiae ; Fructose-1,6-bisphosphatase ; Glucose repression ; Gene activation ; Gluconeogenesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Fructose-1,6-bisphosphatase is a key enzyme in gluconeogenesis and the FBP1 gene is not transcribed during growth with glucose. Genetic analysis indicated a positive regulation of FBP1 expression after exhaustion of glucose. By linker-deletion analysis, two upstream activation sites (UAS1 and UAS2) were localized and the respective UAS-binding factors (DAP I and DAP II for derepression activating protein) were identified by gel retardation. UAS1 and UAS2 span about 30 bp each, and are separated by approximately 30 bp. Both UAS sites act synergistically. Although UAS1 showed some similarities to the DNA-binding consensus for the general yeast activator Rap1, competition experiments and DEAE-chromatography proved that DAP I and Rap1 correspond to different proteins. Gel retardation by DAP I depended on carbon sources and did not occur in cells growing logarithmically with glucose, whereas a strong retardation signal was obtained with ethanol-grown cells. The present results suggest that DAP I and DAP II are the final regulatory elements for glucose derepression.
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  • 3
    ISSN: 1432-0983
    Keywords: Saccharomyces cerevisiae ; Isocitrate lyase ; Gene regulation ; Ethanol induction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The ICL1 gene encoding the isocitrate lyase from Saccharomyces cerevisiae was cloned and sequenced. A reading frame of 557 amino acids showing significant similarity to isocitrate lyases from seven other species could be identified. Construction of icl1 null mutants led to growth defects on C2 carbon sources while utilization of sugars or C3 substrates remained unaffected. Using an ICL1-lacZ fusion integrated at the ICL1 locus, a more than 200-fold induction of β-galactosidase activity was observed after growth on ethanol when compared with glucose-repressed conditions. A preliminary analysis of the ICL1 upstream region identified a 364-bp fragment necessary and sufficient for this regulatory phenotype. Sequence motifs also present in the upstream regions of co-regulated genes were found within this region.
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  • 4
    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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  • 5
    ISSN: 0947-5117
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Investigations into the electrolytic-potentiostatic etching of stainless steels in 10 n NaOH, using a coulometerCurrent density/potential characteristics can only provide qualitative indications concerning the phenomena encountered with potentiostatic etching in 10 n NaOH. The process is best carried out in the trans-passive zone. Identification is based, not on the selective dissolution of certain standard components, but on the interference colours which can be observed as a result of the formation of cover layers of different thickness. The charge density/time characteristics also permit quantitative indications of the different phases. Current density/time curves permit a clarification of the mechanism govering the formation of cover layers. A ferritic steel (28 pC Cr) and a NiCr alloy (45 pC Cr) were found to follow a cubic law of growth, whilst CrNi steel 18-8 is initially governed by an approximately logarithmic law, followed by a zone extending over several hours where the growth begins to follow a parabolic law.
    Notes: Stromdichte-Potential-Kurven ermöglichen nur qualitative Aussagen über die Vorgänge beim potentiostatischen Ätzen in 10 n NaOH. Am günstigsten ist Ätzen im Transpassivbereich. Die Identifizierung erfolgt dabei nicht durch selektive Auflösung bestimmter Gefügebestandteile, sondern aufgrund der Interferenzfarben, die infolge der Bildung unterschiedlich starker Deckschichten zu beobachten sind. Die Ladungsdichte-Zeit-Kurven ermöglichen auch Aussagen über die Mengen der einzelnen Phasen. Stromdichte-Zeit-Kurven ermöglichen eine Aufklärung des Deckschichtbildungsmechanismus. Für einen ferritischen Stahl (28% Cr) und eine NiCr-Legierung mit 45% Cr gilt ein kubisches Wachstumsgesetz, während für CrNi-Stahl 18-8 zunächst ein annähernd logarithmisches Gesetz gilt, an das sich ein mehrstündiger Bereich anschließt, in dem übergang zu einem parabolischen Schichtwachstum erfolgt.
    Additional Material: 24 Ill.
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  • 6
    ISSN: 0947-5117
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: The relationship of the intercrystalline corrosion of a non-stabilised 18/10-chromium-nickel steel with some test solutions and with the potential in boiling 2 n H2SO4Specimens of an austenitic 18/20 nickelchromium steel with about 0.06 pC C, quenched at 1300° C and annealed for different periods of time at 550 or 675° C were potentiostatically subjected to the attack of boiling 2n-H2SO4, of a nitric / hydrofluoric acid pickle at room temperature, and of boiling acids in accordance with the Strauss, Huey and Streicher test. Subsequently, the corrosion rates were determined by weighing and the corrosion examined by visual inspection and microscopically.In the active and passive condition grain boundary corrosion is only encountered after sensitizing annealing. In this connection, the potential merely determines the intensity of the grain boundary attack, but not its occurrence as such. The influence of the potential is more marked at higher than at lower sensitizing annealing temperatures. The test results can easily be interpreted with the aid of the chrome reduction theory.In the transition zone to the transpassive condition, and in the latter, an intercrystalline corrosion attack occurs which depends but little on the sensitizing annealing, and which also occurs with solution-annealed specimens. It is also in this zone of the potential that the non-potentiostatic tests according to Huey and Streicher are carried out.The test results show a specific reaction to chrome reduction of the corrosion attack in the active and passive condition, i.e. the attack in the hydrofluoric/nitric acid pickle and in the Strauss solution. In contrast, the Huey and Streicher tests additionally bring in other properties which, in the main, have an influence on the excess potential of the cathodic part-reaction. These testing agents cannot be regarded as specific criteria for the grain decomposition proneness.
    Notes: Proben eines austenitischen 18/10-Chrom-Nickel-Stahles mit etwa 0,06% C, die von 1300° C abgeschreckt und verschieden lange bei 550 und 675° C geglüht worden waren, wurden potentiostatisch dem Angriff siedender 2n-H2SO4, einer Salpetersäure-Flußsäure-Beize bei Raumtemperatur sowie dem Angriff siedender Säuren entsprechend dem Strauß, Huey- und Streicher-Test unterworfen. Anschließend werden die Korrosionsgeschwindigkeiten durch Wägung bestimmt und der Korrosionsangriff visuell und mikroskopisch im Schliffbild untersucht.Im Aktiv- und Passivzustand tritt Korngrenzenkorrosion nur nach einer Sensibilisierungsglühbehandlung auf. Das Potential bestimmt hierbei nur die Intensität des Korngrenzenangriffs und nicht das Auftreten desselben an sich. Der Einfluß des Potentials ist bei hohen Sensibilisierungslühtemperaturen stärker ausgeprägt, als bei niedrigen Temperaturen. Die Versuchsergebnisse lassen sich mit Hilfe der Chromverarmungstheorie zwanglos deuten.Im Übergangsbereich zum Transpassivzustand erfolgt ein interkristalliner Angriff, der nur wenig von der Sensibilisierungsglühbehandlung abhängt und auch bei lösungsgeglühten Proben auftritt. In diesem Potentialbereich erfolgen auch die nicht potentiostatischen Prüfungen nach Huey und Streicher.Die Versuchsergebnisse zeigen, daß der Angriff im Aktiv- und Passivzustand, also der Angriff in der Flußsäure-Salpeter- Beize und in der Straußschen Lösung, spezifisch auf Chromverarmung ansprechen. Beim Huey- und Streicher-Test werden dagegen zusätzlich noch Eigenschaften, die im wesentlichen die Überspannung der kathodischen Teilreaktion beeinflussen, miterfaßt. Diese Prüfmittel können nicht als spezifisch für die Kornzerfallsanfälligkeit angesehen werden.
    Additional Material: 9 Ill.
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  • 7
    ISSN: 0947-5117
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Precipitation and corrosion behaviour of unstabilized and stabilized 18 10 CrNi steels after short term sensibilizing annealingThe authors have studied the precipitation behaviour of the steels X5 CrNi 18 9, X10CrNiTi 18 9 and X 10CrNiNb 18 9 after solution and sensibilization annealing, and the intercrystalline corrosion behaviour in the Straußtest. On the basis of the results obtained it was possible to determine the and carbonitrides and to define the grain segregation ranges. In the case of the unstabilized materials the behaviour is a function of the formation of chromium depleted zones. However, it is not absolute value of the depletion at the carbid/austenite interphase which controls corrosion, but the depletion in an adjacent zone of measurable thickness. Beyond that the Huey test allows the corrosion susceptibility to be determined in those regions where no continuous chromium depleted zone exists. In the case of stabilized steels the corrosion behaviour depends in addition from carbonitride precipitation, since these compounds are heavily attacked by the boiling nitride acid.
    Notes: Die Verfasser untersuchten das Ausscheidungsverhalten der Stähle X 5 CrNi 18 9, X 10CrNiTi 18 9 und X 10CrNiNb 18 9 nach Lösungs- und Sensibilisierungsglühen sowie das Verhalten gegen interkristalline Korrosion im Strauß-Versuch. Aufgrund der Ergebnisse konnte die Art der Ausscheidungen bestimmt werden (Karbid M23C6 und Karbonitride) und auch die Kornzerfallsbereiche konnten definiert werden. Im Falle des nichtstabilisierten Materials ist das Verhalten abhängig von der Bildung von chromveramten Zonen; dabei ist jedoch nicht die absolute Höhe der Verarmung an der Grenzfläche Kabid/Austenit ausschlaggebend, sondern vielmehr die Verarmung in einer Zone meßbarer Dicke. Im Huey-Versuch läßt sich außerdem die Korrosionsanfälligkeit in den Zonen ermitteln, wo keine zusammenhängende Chromverarmungszone vorliegt. Im Falle der stabilisierten Stähle ist das Korrosionsverhalten außerdem abhängig von der Karbonitridausscheidung, da diese Ausscheidungen von der siedenden Salpetersäure stark angegriffen werden.
    Additional Material: 12 Ill.
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  • 8
  • 9
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