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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Cellular and molecular life sciences 56 (1999), S. 807-816 
    ISSN: 1420-9071
    Keywords: Key words. Yeast; aging; senescence; helicase; silencing; nucleolus; metabolism; retrograde signaling.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. The molecular mechanisms of aging are most fully understood for the budding yeast Saccharomyces cerevisiae. Recent advances in our understanding of aging in this organism have enabled researchers to answer some fundamental questions about the aging process. Is aging due to a multitude of ‘mechanisms’ or can there be a key few? Can we design single-gene mutations that will prolong life? Can we prolong life whilst maintaining health and fecundity? The various contributing factors to yeast longevity, uncovered thus far, fall into three classes: DNA metabolism, heterochromatin, and metabolic activity. However, these separate classes may actually represent different aspects of the same aging mechanism based on genome stability. This review examines the recent advances in our understanding of yeast aging and discusses their relevance, if any, to the human condition.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1617-4623
    Keywords: Key words Polycomb group ; Trithorax group ; Homeotic mutations ; Drosophila melanogaster
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The protein products of Polycomb group (PcG) and trithorax group (trxG) genes are required for the maintenance of the transcriptionally repressed and active states, respectively, of the homeotic genes. Mutations in PcG genes produce gain-of-function (posterior) homeotic transformations, while mutations in trxG genes produce loss-of-function (anterior) homeotic transformations. Double mutant combinations between a PcG gene and a trxG gene suppress the homeotic transformations seen with either mutation alone, suggesting that PcG and trxG genes act antagonistically. The PcG gene Additional sex combs (Asx) is interesting because one mutant allele, Asx P1 , causes both anterior and posterior homeotic transformations. Asx P1 and other Asx mutations were crossed to mutations in the PcG gene Polycomb (Pc) and the trxG gene trithorax (trx). Asx alleles enhance both PcG and trxG homeotic transformations, showing that Asx is required for both the activation and the repression of homeotic loci. Asx also shows strong allele-specific interactions with the PcG genes Pc and super sex combs (sxc). Together, these data indicate that there are functional interactions between Asx, Pc and sxc in vivo. ASX may interact with a PcG complex containing PC and SXC and mediate activation versus repression at target loci, perhaps by interacting directly with the TRX protein.
    Type of Medium: Electronic Resource
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  • 3
    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 Spark-plasma-sintering (SPS) has been applied to BaTiO3 to prepare dense ceramics consisting of submicrometre-sized powder. Relatively dense (typically 97% of the theoretical X-ray density) pellets with an average grain size remaining similar to that of the starting powder, approximately 0.6 μm, were obtained by the SPS process. Fixed frequency (1 kHz) measurements show the room temperature permittivity of SPS ceramics to be relatively high, approximately 3500, and at least double the value of conventionally sintered ceramics, approximately 1500. Alternating current (a.c.) impedance spectroscopy measurements show that SPS is an effective process to reduce the influence of intergranular (grain boundary) effects on the permittivity and direct current (d.c.) resistance characteristics of BaTiO3 ceramics substantially.
    Type of Medium: Electronic Resource
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