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  • 1
    Electronic Resource
    Electronic Resource
    Autoregulation of the Escherichia coli replication initiator protein, DnaA, is indirect (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 23 (1997), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The expression of dnaA is autoregulated, in that transcription of the gene increases when DnaA is inactivated (and initiation of replication prevented) and decreases when DnaA is supplied in excess. However, the inactivation of DnaA does not necessarily lead to increased DnaA production, as dnaA(7s; temperature sensitive) strains which are integratively suppressed by derivatives of the plasmid R1 do not show temperature-induced derepression. Several possible explanations for this unanticipated behaviour were considered and ruled out. We suggest here that the completion of a critical step in initiation may prevent dnaA derepression: although DnaA would be required to complete this step at oriC, DnaA(Ts) would be sufficient at the R1 origin. Autoregulation of dnaA has been attributed to the binding of DnaA at a consensus binding site in the dnaA promoter region. We show here, using reporter systems, that this DnaA-binding site is not required for the autoregu-latory response. We find, further, that replacement of the chromosomal dnaA gene with one containing a mutated binding site causes no demonstrable pheno-typic change: cells with the mutant gene show no disadvantage in competition with dnaA+ cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1997.3121675.x
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  • 2
    Electronic Resource
    Electronic Resource
    Cs2Ga2O(BO3)2 (1995)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 51 (1995), S. 547-549 
    Details
    ISSN: 1600-5759
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108270194009418
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  • 3
    Electronic Resource
    Electronic Resource
    Multi-instrument probing of the polar ionosphere under steady northward IMF (1999)
    Springer
    Annales geophysicae 18 (1999), S. 90-98 
    Details
    ISSN: 0992-7689
    Keywords: Ionosphere (polar ionosphere) ; Magnetospheric physics (magnetosphere-ionosphere interactions; polar cap phenomena)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Observations are presented of the polar ionosphere under steady, northward IMF. The measurements, made by six complementary experimental techniques, including radio tomography, all-sky and meridian scanning photometer optical imaging, incoherent and coherent scatter radars and satellite particle detection, reveal plasma parameters consistent with ionospheric signatures of lobe reconnection. The optical green-line footprint of the reconnection site is seen to lie in the sunward plasma convection of the lobe cells. Downstream in the region of softer precipitation the reverse energy dispersion of the incoming ions can be identified. A steep latitudinal density gradient at the equatorward edge of the precipitation identifies the general location of an adiaroic boundary, separating the open field lines of polar lobe cells from the closed field of viscous-driven cells. Enhancements in plasma density to the south of the gradient are interpreted as ionisation being reconfigured as it is thrust against the boundary by the antisunward flow of the viscous cells near noon. Each of the instruments individually provides valuable information on certain aspects of the ionosphere, but the paper demonstrates that taken together the different experiments complement each other to give a consistent and comprehensive picture of the dayside polar ionosphere.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-000-0090-2
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  • 4
    Electronic Resource
    Electronic Resource
    Observations of thermospheric neutral winds within the polar cusp and the auroral oval using a Doppler imaging system (DIS) (1998)
    Springer
    Annales geophysicae 16 (1998), S. 1461-1474 
    Details
    ISSN: 0992-7689
    Keywords: Ionosphere (Polar ionosphere) ; Meteorology and atmospheric dynamics (thermospheric dynamics; instruments and techniques)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Two Doppler imaging systems (DIS) or wide-field imaging Fabry-Perot interferometers (FPI), have recently been commissioned, one at the Auroral Station, Adventdalen, Longyearbyen, Svalbard, and the second at the IRF, Kiruna, Sweden. These instruments can provide wide-field (600 * 800 km) images of neutral wind flows in the upper thermosphere, by measuring the Doppler shift of the atomic oxygen forbidden near 630 nm, which is emitted from an altitude of approximately 240 km. From the instrument in Svalbard, at mid-winter, it is possible to observe the dayside polar cusp and the polar cap throughout the entire day, whereas from Kiruna, the night-time auroral oval is observable during the hours of darkness. Measurements of thermospheric dynamics from the DIS can be used in conjunction with observations of ionospheric plasma flows and thermal plasma densities by the EISCAT-Svalbard radar (ESR) and by EISCAT, along with other complementary observations by co-located instruments such as the auroral large-scale imaging system (ALIS). Such combined data sets will allow a wide range of scientific studies to be performed concerning the dynamical response of the thermosphere and ionosphere, and the important energetic and momentum exchange processes resulting from their complex interactions. These processes are particularly important in the immediate vicinity of the polar cusp and within the auroral oval. Early results from Svalbard in late 1995 will be discussed. The DIS in Kiruna observed two interesting geomagnetic disturbances in early 1997, the minor geomagnetic storm of 10, 11 January, and the disturbed period from 7–10 February. During these events, the thermospheric wind response showed some interesting departures from the average behaviour, which we attribute to the result of strong and variable Lorenz forcing (ion drag) and Joule and particle heating during these geomagnetic disturbances.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-998-1461-3
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  • 5
    Electronic Resource
    Electronic Resource
    Protein synthesis and oxygen consumption in fish cells (1995)
    Springer
    Journal of comparative physiology 165 (1995), S. 93-101 
    Details
    ISSN: 1432-136X
    Keywords: Protein synthesis ; Oxygen consumption ; Energetic cost ; Fish cells ; Trout, Oncorhynchus mykiss
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Oxygen consumption and protein synthesis were measured concurently in four fish cell types: BF-2 and TRG-2 cell lines, rainbow trout macrophages and scale cells. The fractional rates of protein synthesis (percentage of the protein mass synthesised per day) were ranked: BF-2 cells 〉 macrophages 〉 RTG-2 cells 〉 scale cells. Oxygen consumption rates were ranked BF-2 cells = macrophages = RTG-2 cells 〉 scale cells. Within three of the cell types (BF-2, RTG-2 and scale cells) oxygen consumption and protein synthesis were linearly correlated, whereas comparison between the four cell types gave rise to an exponential relationship between fractional rates of protein synthesis and oxygen consumption. Inhibition of protein synthesis with cycloheximide by 41–65% resulted in a 62–89% reduction in oxygen consumption depending on cell type. Calculations of the aerobic cost of protein synthesis using the cycloheximide-sensitive protein synthesis and oxygen consumption rates resulted in estimates ranging from 11 to 217 μmol O2·mg protein-1 synthesised depending on the cell type. The lowest net protein synthesis costs, which are close to theoretical values for peptide bond formation, were associated with the most rapid rates of protein synthesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00301473
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