| 1. |
- Santesson, Sabina, et al.
(author)
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Screening of nucleation conditions using levitated drops for protein crystallization
- 2003
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In: Analytical Chemistry. - : American Chemical Society (ACS). - 1520-6882 .- 0003-2700. ; 75:7, s. 1733-1740
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Journal article (peer-reviewed)abstract
- The growth of suitable protein crystals is an essential step in the structure determination of a protein by X-ray crystallography. At present, crystals are mostly grown using trial-and-error procedures, and protocols that rapidly screen for the crystal nucleation step are rare. Presented here is an approach to minimize the consumption of precious protein material while searching for the nucleation conditions. Acoustically levitated drops of known protein concentration (0.25-1.5-L volumes) are injected with crystallizing agents using piezoelectric flow-through dispensers (ejecting 50-100-pL droplets at 1-9000 droplets/s). A restricted number of crystallizing agents representing three classes are used: poly(ethylene glycol), salts, and the viscous alcohol 2-methyl 2,4-pentanediol. From a digitized picture of the levitated drop volume, calculations are performed giving the concentrations of all components in the drop at any time during a "precipitation experiment". Supersaturation is the prerequisite for crystal nucleation, and protein precipitation indicates high supersaturation. A light source illuminates the levitated drop, and protein precipitation is monitored using right-angle light scattering. On the basis of these intensity measurements and the volume determination, precipitation diagrams for each crystallizing agent are constructed that give the protein/crystallizing agent concentration boundaries between the minimum and the maximum detectable protein precipitation. Guided by the concentration values obtained from such plots, when approaching the supersaturation region, separate crystallization drops are mixed and allowed to equilibrate under paraffin oil. At conditions in which microcrystals can be observed, the nucleation tendency of the macromolecule is confirmed. Optimization of crystallization conditions can then follow. Proteins tested include alcohol dehydrogenase and D-serine dehydratase. Alcohol dehydrogenase, known to crystallize easily, was used to evaluate whether the ultrasonic field inhibits nucleation. Details are given for the screening procedure of D-serine dehydratase, an enzyme earlier found to be difficult to crystallize reproducibly. The time and material-saving qualities of this method are emphasized, since a range of conditions can quickly be screened using small amounts of protein to roughly determine solubility characteristics of a protein before crystallization trials are initiated.
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| 2. |
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| 3. |
- Santesson-Wilson, Peter
(author)
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Studier i symbolpolitik
- 2003
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Doctoral thesis (other academic/artistic)abstract
- Symbolic politics is the degree to which political decision-making is motivated, not by the tangible aspects of the decision, but by the interpretation of what the decision represents symbolically. While symbolic politics is widely recognized as an important aspect of political decision-making, the phenomenon is insufficiently explored in political science. The first aim of the present dissertation is to develop and systematize concepts and mechanisms necessary for the study of symbolic politics. The second aim is to make a preliminary evaluation of the explanatory power of the suggested concepts. This is done by applying the concepts in two case studies of current Swedish policy-making. The first case is a study of the decision in 2000 to give state subsidies to broadband Internet connections. The second case is a study of the decision in 1997 to commence the nuclear power phase-out by closing the Barsebäck nuclear power plant. Symbolic politics is suggested to be defined negatively, as being those aspects of a political decision that are not tangible. The taxonomy of symbolic politics consists of four varieties: categories, principles, examples, and expressions. Categories are ways to create a symbolic connection between political issues by cognitively grouping them together. Principles are ways to give the categorization normative implications: since the issues are alike, they should be treated alike. Examples are instances where a single member of the group is offered as prototypical example of the entire group. An expression is the communicative use of political decisions, a deliberate signal or an unintended symptom of the actor’s intentions. The taxonomy of symbolic politics can be incorporated in general theories of policy processes and political decision-making. Categories play an integral part of almost all public policy theories, and can help to explain problem-definition processes. Principles are techniques to expand the scope of a political conflict and mobilize new groups of actors. Examples are important to raise attention, both on an individual level, and on the political agenda. Expressions can be used both to expand and to contract the scope of a political conflict. The first case study, the broadband decision in 2000, reveals a mixture of instrumental and symbolic factors explaining the decision. Broadband connections were used as a prototypical example of Internet and information technology. In order to signal governmental commitment to it, the social democratic government changed their previously demand-based policy towards a more supply-oriented one. The second case study, the decision in 1997 to commence the nuclear power phase-out by closing the Barsebäck nuclear power plant, reveals a similar mixture of motives. It was decided in 1980 that all Swedish nuclear power should be phased-out before 2010. Fifteen years on, the credibility of this decision had successively eroded. By closing one nuclear reactor, and thereby sending a signal reassuring of the government’s commitment to the phase-out, it was possible to abandon the 2010-limit without being accused of disrespecting the popular will. The symbolic political taxonomy is concluded to hold enough promise to warrant further elaboration.
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| 4. |
- Laurie, Andrew D., et al.
(author)
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The role of the alarmone (p)ppGpp in sigma N competition for core RNA polymerase
- 2003
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In: Journal of Biological Chemistry. - : American Society for Biochemistry and Molecular Biology. - 0021-9258 .- 1083-351X. ; 278:3, s. 1494-1503
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Journal article (peer-reviewed)abstract
- Some promoters, including the DmpR-controlled sigma(N)-dependent Po promoter, are effectively rendered silent in cells lacking the nutritional alarmone (p)ppGpp. Here we demonstrate that four mutations within the housekeeping sigma(D)-factor can restore sigma(N)-dependent Po transcription in the absence of (p)ppGpp. Using both in vitro and in vivo transcription competition assays, we show that all the four sigma(D) mutant proteins are defective in their ability to compete with sigma(N) for available core RNA polymerase and that the magnitude of the defect reflects the hierarchy of restoration of transcription from Po in (p)ppGpp-deficient cells. Consistently, underproduction of sigma(D) or overproduction of the anti-sigma(D) protein Rsd were also found to allow (p)ppGpp-independent transcription from the sigma(N)-Po promoter. Together with data from the direct effects of (p)ppGpp on sigma(N)-dependent Po transcription and sigma-factor competition, the results support a model in which (p)ppGpp serves as a master global regulator of transcription by differentially modulating alternative sigma-factor competition to adapt to changing cellular nutritional demands.
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| 5. |
- Madsen, Anni Tindahl, et al.
(author)
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Optical dating of young tidal sediments in the Danish Wadden Sea
- 2007
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In: Quaternary Geochronology. - : Elsevier BV. - 1871-1014. ; 2:1-4, s. 89-94
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Journal article (peer-reviewed)abstract
- We have tested the applicability of optically stimulated luminescence (OSL) to the dating of young estuarine sediments (< 1000 years) to determine whether this method can be used to complement and support existing techniques, such as Pb-210 dating. The degree of bleaching before deposition is investigated by examining the age trend in various sediment cores, and where possible, by comparison with independent age control provided by (21)0Pb dating. The consistency between optical ages and Pb-210 ages is shown to be satisfactory on a time-scale down to only a few years. We conclude that OSL provides reliable and reproducible results in cores from sub-, inter- and supra-tidal sediments, ranging from only a few years up to similar to 1000 years old, confirming its value in the estimation of estuarine accretion rates. With OSL it is, for the first time, possible to date sediment cores from silty and sandy tidal flats, providing a new approach to the problem of evaluation of stability and calculation of sediment budgets for estuaries and coastal lagoons. (c) 2006 Elsevier Ltd. All rights reserved.
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| 6. |
- Paoli, John, 1975
(author)
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Facial Reconstruction after Mohs Surgery
- 2019
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In: Acta Dermato-Venereologica. - : Medical Journals Sweden AB. - 1651-2057 .- 0001-5555. ; 99:4
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Review (other academic/artistic)
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| 7. |
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