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  • 1
    Electronic Resource
    Electronic Resource
    The Primordial Abundance of 3-Helium and Deuterium (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 688 (1993), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1993.tb43967.x
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  • 2
    Electronic Resource
    Electronic Resource
    A novel regulatory system required for pathogenicity of Xanthomonas campestris is mediated by a small diffusible signal molecule (1997)
    Oxford BSL : Blackwell Publishing Ltd
    Molecular microbiology 24 (1997), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Mutations in the seven clustered rpf genes cause downregulated synthesis of extracellular enzymes and reduced virulence of Xanthomonas campestris pathovar campestris (Xcc). The phenotype of mutants in one of the genes, rpfF, can be restored by a diffusible extracellular factor (DSF) produced by all Xcc strains tested, apart from rpfF and rpfB mutants. DSF accumulates in early stationary phase (when synthesis of enzymes is maximal), but levels decline subsequently. Addition of DSF to exponentially-growing wild-type bacteria does not cause precocious enzyme synthesis. rpfB and rpfF are expressed throughout growth, but the rate increases in early stationary phase. RpfB is predicted to be a long-chain fatty acyl CoA ligase, and RpfF shows some relatedness to enoyl CoA hydratases. The properties of DSF suggest that it may be a fatty-acid derivative, and certain lipid preparations possess DSF activity at higher concentrations. These include lipid extracts and acid-hydrolysed lipopolysaccharide and lipid A from Xcc, and purified dodecanoic and hydroxydodecanoic acid. DSF production is confined to certain xanthomonads. We propose a model for the DSF system, which represents a novel mechanism for regulating virulence factor synthesis in response to physiological or environmental changes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1997.3721736.x
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  • 3
    Electronic Resource
    Electronic Resource
    Towards an understanding of the structural basis of ‘forbidden’ transport pathways in the Escherichia coli lactose carrier: mutations probing the energy barriers to uncoupled transport (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 4 (1990), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Recent progress in the analysis of mutants of the Eschenchia coli lactose carrier function is reviewed, with special emphasis on the structural basis for energy barriers which prevent ‘forbidden’ con-formational changes. Mutations which break down the barriers to forbidden isomerizations involving the binary carrier:sugar (CS) and carrier:proton (CH) complexes have been obtained in several laboratories. These mutants allow uncoupled transport of H+ or galactoside in the lactose carrier which normally couples cation and sugar movement in a 1:1 stoichiometry. These uncoupled mutants appear to be associated with changes in both sugar and cation recognition, suggesting that the physical interactions forming the basis for co-substrate recognition and uncoupling are not independently variable.By postulating that translocation involves transformation of the stable intermediate of the co-transport cycle to unstable transition state conformations of the carrier, it is possible to consider the consequences of mutagenesis in terms of transition state theory. Consistent with several experimental observations, the analysis predicts in each mutant the occurrence of more than one abnormality in the transport cycle (such as changes in sugar recognition, cation recognition or the coupling reaction). We have called the general phenomenon a ‘mutational double-effect’ because any mutation which alters the Gibbs free energy change of one reaction in the transport
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1990.tb02053.x
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  • 4
    Electronic Resource
    Electronic Resource
    The rpfA gene of Xanthomonas campestris pathovar campestris, which is involved in the regulation of pathogenicity factor production, encodes an aconitase (1998)
    Oxford BSL : Blackwell Publishing Ltd
    Molecular microbiology 28 (1998), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Xanthomonas campestris pv campestris (Xcc) is a plant pathogenic bacterium that controls the production of pathogenicity factors in part by a cluster of genes designated rpf (regulation of pathogenicity factors). Sequence analysis of one of these genes (rpfA) revealed an open reading frame with amino acid sequence similarity to aconitases from other bacteria. Aconitase activity was lower in cellular extracts of an rpfA::Tn5 mutant than in those from the wild type. A zymogram of aconitase activity after native gel electrophoresis showed the presence of two distinct aconitases in Xcc; the major aconitase was absent in the rpfA::Tn5 mutant. This mutant also had reduced levels of extracellular enzymes and extracellular polysaccharide (EPS). Supplying rpfA in trans to the rpfA::Tn5 mutant restored both the major aconitase activity and the synthesis of these pathogenicity factors. The transcription of the genes for two extracellular enzymes (prtA, encoding a serine protease, and engXCA, encoding endoglucanase) was reduced in the rpfA mutant background. Because some eukaryotic aconitases are also involved in iron regulation, we explored a possible connection between rpfA and iron metabolism. Intracellular iron levels in the mutants were lower than in the wild type as assessed by sensitivity to the iron-activated antibiotic, streptonigrin. Wild-type bacteria grown in iron-deficient conditions had a similar sensitivity to streptonigrin as the aconitase mutant. Overall, these results suggest that a prokaryotic aconitase can also act as a regulator of gene expression and that the regulation is possibly related to changes in intracellular iron levels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1998.00852.x
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  • 5
    Electronic Resource
    Electronic Resource
    Leaf teeth, transpiration and the retrieval of apoplastic solutes in balsam poplar (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 83 (1991), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The rapid flow of the transpiration stream through major veins to leaf teeth was followed in leaves of Populus balsamifera L., using the tracer sulphorhodamine G (SR), which probes for cells with H+-extrusion pumps. The tracer accumulated quickly in the hydathodes of the teeth. It was shown by freeze-substitution and anhydrous processing that SR was taken up by phloem parenchyma and epithem cells of the hydathode. When 14C-labelled aspartate was fed to the leaves in the transpiration stream, it also was taken up most strongly by the same phloem parenchyma and epithem cells. It is proposed that one function of the hydathodes in leaf teeth is the retrieval of solutes from the transpiration stream.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1991.tb02146.x
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  • 6
    Electronic Resource
    Electronic Resource
    Proton pump activity in bundle sheath tissues of broad-leaved trees in relation to leaf age (1988)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 73 (1988), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The fluorescent probe sulphorhodamine G (SR) has been previously used as an indicator of low extra-cellular pH and, by inference, of proton extrusion activity in living leaves. In legumes the SR uptake and proton extrusion was characteristic of the extended bundle sheath system (EBS) or paraveinal mesophyll, composed of bundle sheath cells and the related network of bridging cells between veins. This system has been identified as a site of temporary storage of amino carbon in soybean. A tree species. Populus deltoides Bartr. ex Marsh, was known both to have the EBS system in its leaves and to carry organic nitrogen in its xylem sap. It is now shown that P. deltoides also accumulates the SR probe in the EBS system. This association has been explored in 8 other broad-leaved tree species. Seven of the 8 species have EBS systems and accumulate SR in them in early summer. The 8th species, Tilia americana L. has no EBS system and shows weak SR accumulation. The capacity to accumulate SR (and by inference to scavenge solutes from the transpiration stream) disappeared in all species at various stages in late summer. In two species, in addition, SR accumulation is interrupted for several weeks during fruit growth. It is proposed that EBS systems will be found in many dicotyledonous leaves, and will be found to scavenge solutes, especially organic nitrogen, from the xylem sap.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1988.tb05427.x
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  • 7
    Electronic Resource
    Electronic Resource
    A sampling artefact affecting the uranium content of deep-sea porewaters obtained from cores (1984)
    [s.l.] : Nature Publishing Group
    Nature 308 (1984), S. 263-266 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The porewaters were collected on RRS Discovery Cruise 129 in 1982, using the Institute of Oceanographie Sciences (IOS) Mark II in situ porewater sampler12, a box corer13 to retrieve short sediment sections with undisturbed interfaces, and a Kastenlot corer to recover longer (2 m) sections. Subcores ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/308263a0
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  • 8
    Electronic Resource
    Electronic Resource
    Hydrographic Observations on the Red Sea Brines indicate a Marked Increase in Temperature (1971)
    [s.l.] : Nature Publishing Group
    Nature 231 (1971), S. 37-38 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] During February 1971, R/V Chain revisited the brine area. Although it will be several months before the chemical data are complete, the hydrographic data gathered are of immediate interest. The most unusual observation is that the temperature of the Atlantis II brine has risen 2.7 C from 56.5 C to ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/231037a0
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  • 9
    Electronic Resource
    Electronic Resource
    Percentage Number of Nonthermal Sources in the Northern and Southern Halves of the Galaxy (1970)
    [s.l.] : Nature Publishing Group
    Nature 225 (1970), S. 245-246 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] A method of detecting galactic supernova remnants, using a radio telescope at a single frequency, would be to examine a large number of radio sources and then select those sources from the sample which do not exhibit radio recombination lines. Because of the weakness of the recombination lines (the ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/225245b0
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  • 10
    Electronic Resource
    Electronic Resource
    Evidence for denitrification in aerobic pelagic sediments (1978)
    [s.l.] : Nature Publishing Group
    Nature 274 (1978), S. 354-356 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Data on the dissolved oxygen and nitrogen content of pelagic sediments have hitherto not been available, although results from some near-shore environments have been reported4. There are considerable difficulties in sampling deep-sea sedimentary pore waters for dissolved gases and in analysing the ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/274354a0
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