Showing papers by "University of Konstanz published in 1994"

Ideas do not float freely: transnational coalitions, domestic structures, and the end of the cold war

Abstract: Realist or liberal explanations for the end of the cold war cannot account for the specific content of the change in Soviet foreign policy or for Western responses to it. These theories need to be complemented by approaches that emphasize the interaction between international and domestic factors and that take seriously the proposition that ideas intervene between structural conditions and actors' interests. Some of the strategic prescriptions that informed the reconceptualization of Soviet security interests originated in the Western liberal internationalist community, which formed transnational networks with “new thinkers” in the former Soviet Union. These new ideas became causally consequential for the turnaround in Soviet foreign policy and also had an impact on American and German reactions to it. Even though transnational networks were active in Germany, the Soviet Union, and the United States, their success varied. Domestic structures like the nature of political institutions, state-society relations, and political culture determine the ability of transnational networks first, to gain access to a country's political system and second, to build “winning coalitions.” These differences in domestic structures can largely explain the variation in impact of the strategic prescriptions among the three countries.

The cellular concentration of the sigma S subunit of RNA polymerase in Escherichia coli is controlled at the levels of transcription, translation, and protein stability.

Abstract: The second vegetative sigma factor sigma S (encoded by the rpoS gene) is the master regulator in a complex regulatory network that governs the expression of many stationary phase-induced and osmotically regulated genes in Escherichia coli. Using a combination of gene-fusion technology and quantitative immunoblot, pulse-labeling, and immunoprecipitation analyses, we demonstrate here that rpoS/sigma S expression is not only transcriptionally controlled, but is also extensively regulated at the levels of translation and protein stability. rpoS transcription is inversely correlated with growth rate and is negatively controlled by cAMP-CRP. In complex medium rpoS transcription is stimulated during entry into stationary phase, whereas in minimal media, it is not significantly induced. rpoS translation is stimulated during transition into stationary phase as well as by an increase in medium osmolarity. A model involving mRNA secondary structure is suggested for this novel type of post-transcriptional growth phase-dependent and osmotic regulation. Furthermore, sigma S is a highly unstable protein in exponentially growing cells (with a half-life of 1.4 min), that is stabilized at the onset of starvation. When cells are grown in minimal glucose medium, translational induction and sigma S stabilization occur in a temporal order with the former being stimulated already in late exponential phase and the latter taking place at the onset of starvation. Although sigma S does not control its own transcription, it is apparently indirectly involved in a negative feedback control that operates on the post-transcriptional level. Our analysis also indicates that at least five different signals [cAMP, a growth rate-related signal (ppGpp?), a cell density signal, an osmotic signal, and a starvation signal] are involved in the control of all these processes that regulate rpoS/sigma S expression.

Heterocyst Metabolism and Development

Abstract: Heterocysts are differentiated cells that are specialized for fixation of N2 in an aerobic environment. In heterocysts in the light, Photosystem I generates ATP, but no photosynthetic production of O2 takes place. Instead, reductant moves into heterocysts from vegetative cells. In return, fixed nitrogen moves from heterocysts to vegetative cells. In neither case is there certainty about the identity of the traffic molecules. Pathways of electron-donation to N2 have been extensively investigated, but their in-vivo importance remains to be critically tested. Nitrogenase in heterocysts is protected from inactivation by O2 by a variety of means, principally by enhanced respiration and by a barrier, the heterocyst envelope, to entry of O2. However, the respiratory apparatus and the biosynthetic processes that result in synthesis of the barrier have been little studied. The detailed mechanisms underlying metabolic, environmental, and developmental control of nitrogenase are under investigation. Studies of heterocyst development are being greatly facilitated by recent advances in the genetics of Anabaena sp. An autoregulated gene, hetR, that is activated shortly after nitrogen-stepdown is critical for the differentiation of heterocysts. Two enigmas remain to be answered: how is it determined which cells will differentiate; and, after differentiation is initiated, what intercellular interactions and intracellular mechanisms regulate the progression of the differentiation process? An evolutionary and biochemical relationship between the processes leading to the formation of heterocysts and akinetes is suggested.

Murine hepatocyte apoptosis induced in vitro and in vivo by TNF-alpha requires transcriptional arrest.

Abstract: Freshly isolated mouse hepatocytes were essentially insensitive to TNF-alpha cytotoxicity. However, TNF-alpha induced a concentration-dependent cell death in hepatocytes that had been pretreated with the transcriptional inhibitors actinomycin D (ActD), D-galactosamine, or alpha-amanitin. Unlike RNA synthesis inhibition, a translational block in the presence of cycloheximide (CHX) or puromycin did not sensitive hepatocytes to TNF. On the contrary, these agents prevented hepatocytotoxicity induced by ActD/TNF. Pretreatment with peroxides or glutathione depletors had no significant influence on TNF cytotoxicity. In vivo treatment of mice with ActD/TNF caused hepatic failure, which was significantly reduced by co-treatment with CHX. These findings demonstrate that protein synthesis is required for this mechanism of cell death. To test whether TNF may trigger an endogenous suicide program in hepatocytes, we examined whether DNA fragmentation preceded cell death. In the culture system, hepatocellular DNA fragmentation in the presence of ActD/TNF was observed several hours before lactate dehydrogenase release and was inhibited by CHX. Similar results were obtained in vivo. Chromatin condensation and the formation of apoptotic bodies were observed in livers from mice treated with ActD/TNF and significant DNA fragmentation was detected as early as 4 h after challenge. At this time, organ total glutathione content and plasma transaminase levels were not significantly different from those of untreated controls. The findings of this study demonstrate that direct hepatotoxicity of TNF-alpha is associated with an apoptotic mechanism that becomes manifest under the metabolic condition of arrested transcription and functional translation.

Complete Dna-Sequence Of Yeast Chromosome-Xi

Abstract: The complete DNA sequence of the yeast Saccharomyces cerevisiae chromosome XI has been determined. In addition to a compact arrangement of potential protein coding sequences, the 666,448-base-pair sequence has revealed general chromosome patterns; in particular, alternating regional variations in average base composition correlate with variations in local gene density along the chromosome. Significant discrepancies with the previously published genetic map demonstrate the need for using independent physical mapping criteria.

User modeling and user-adapted interaction

Abstract: User modeling has made considerable progress during its existence now of more than a decade. Particularly in the last few years, the need has been recognized in many application areas for software systems to automatically adapt to their current users. As a result, research on user modeling has extended into many disciplines which are concerned with the development of interactive computer systems that are used by heterogeneous user populations. These fields include Intelligent Interfaces, Active and Passive Help Systems, Guidance Systems, Hypertext Systems, Intelligent Information Retrieval, Natural-Language Systems, Intelligent Tutoring Systems, and Cooperative Expert Systems. Applications in office machines, consumer electronics and automobiles are also being envisioned. Several recent empirical evaluations provide support for the usefulness of user-adaptation in the investigated application domains.

Adaptation of Escherichia coli to high osmolarity environments: Osmoregulation of the high-affinity glycine betaine transport system ProU

Abstract: A sudden increase in the osmolarity of the environment is highly detrimental to the growth and survival of Escherichia coli and Salmonella typhimurium since it triggers a rapid efflux of water from the cell, resulting in a decreased turgor. Changes in the external osmolarity must therefore be sensed by the microorganisms and this information must be converted into an adaptation process that aims at the restoration of turgor. The physiological reaction of the cell to the changing environmental condition is a highly coordinated process. Loss of turgor triggers a rapid influx of K+ ions into the cell via specific transporters and the concomitant synthesis of counterions, such as glutamate. The increased intracellular concentration of K(+)-glutamate allows the adaptation of the cell to environments of moderately high osmolarities. At high osmolarity, K(+)-glutamate is insufficient to ensure cell growth, and the bacteria therefore replace the accumulated K+ ions with compounds that are less deleterious for the cell's physiology. These compatible solutes include polyoles such as trehalose, amino acids such as proline, and methyl-amines such as glycine betaine. One of the most important compatible solutes for bacteria is glycine betaine. This potent osmoprotectant is widespread in nature, and its intracellular accumulation is achieved through uptake from the environment or synthesis from its precursor choline. In this overview, we discuss the properties of the high-affinity glycine betaine transport system ProU and the osmotic regulation of its structural genes.

Quantum phase of a moving dipole.

Abstract: It is shown that a neutral particle with an electric dipole moment which moves in a magnetic field acquires a topological phase. This phase may be observed in atom or molecular interferometry.

Holophaga foetida gen. nov., sp. nov., a new, homoacetogenic bacterium degrading methoxylated aromatic compounds.

Abstract: A polyphasic approach was used in which genotypic and phenotypic properties of a gram-negative, obligately anaerobic, rod-shaped bacterium isolated from a black anoxic freshwater mud sample were determined. Based on these results, the name Holophaga foetida gen. nov., sp. nov. is proposed. This microorganism produced dimethylsulfide and methanethiol during growth on trimethoxybenzoate or syringate. The only other compounds utilized were pyruvate and trihydroxybenzenes such as gallate, phloroglucinol, or pyrogallol. The aromatic compounds were degraded to acetate. Although comparison of the signature nucleotide pattern of the five established subclasses of Proteobacteria with the 16S rDNA sequence of Holophaga foetida revealed a relationship to members of the δ-subclass, the phylogenetic position within the radiation of this class is so deep and dependent upon the number and selection of reference sequences that its affiliation to the Proteobacteria must be considered tentative. The type strain is H. foetida strain TMBS4 (DSM 6591).

Gap‐43 immunoreactivity and axon regeneration in retinal ganglion cells of the rat

Abstract: SUMMARY Retinal ganglion ceHs (RGCs) in rats were retrogradely labeled with the fluorescent tracer Fluorogold (FG) and subjected to GAP-43 and c-JUN immunocytochemistry to identify those RGCs that are capable of regenerating an axon. After optic nerve section (ONS) and simulta­ neous application of FG to the nerve stump (group 1 experiments), GAP-43 immunoreactive RGCs (between 2 and 21 days after ONS) always represented a subfrac­ tion ofboth FG-Iabeled (Le., surviving) RGCs and RGCs exhibiting c-JUN. GAP-43 immunoreactive RCCs repre­ sented 22% of RGCs normally present in rat retinae and 25% of surviving RGCs at 5 days after ONS but were reduced to 2% and 1%, wh ich is 6% and 5% ofsurvivors at 14 and 21 days, respectively. In animals that received a peripheral nerve (PN) graft after ONS (group 2 experi­ ments), RGCs with regenerating axons were identified by FG application to the graft at 14 and 21 days. When

Nucleic-acid-binding properties of hnRNP-U/SAF-A, a nuclear-matrix protein which binds DNA and RNA in vivo and in vitro

Abstract: We show that SAF-A, a nuclear protein which specifically binds vertebrate scaffold-attachment-region (SAR) elements with high affinity is identical with hnRNP-U, assumed to be involved in packaging of hnRNA in ribonucleoprotein particles. Ultraviolet cross-linking experiments show that the protein, referred to as hnRNP-U/SAF-A, is bound to chromosomal DNA in vivo. In vitro, the isolated protein binds to double-stranded and single-stranded DNA and forms higher ordered nucleic-acid-protein complexes. Filter-binding experiments performed with different types of natural and synthetic nucleic acids as substrates show that the protein binds DNA and RNA with different affinities and most likely at different binding sites. We conclude that hnRNP-U/SAF-A thus may have functions in the organisation of chromosomal DNA in addition to its suggested role in hnRNA metabolism.

Schemes for atomic-state teleportation

Abstract: We present two schemes employing cavity QED phenomena to realize the teleportation of quantum states following the principle outlined by Bennett et al [Phys Rev Lett 70, 1895 (1993)]

Partial reactions of the Na,K-ATPase: determination of rate constants.

Abstract: Experiments were designed to characterize several partial reactions of the Na,K-ATPase and to demonstrate that a model can be defined that reproduces most of the transport features of the pump with a single set of kientic parameters. We used the fluorescence label 5-iodoacetamidofluorescein, which is thought to be sensitive to conformational changes, and the styryl dye RH 421, which can be applied to detect ion-binding and -release reactions. In addition transient electric currents were measured, which are associated mainly with the E1-->E2 conformational transition. Numerical simulations were performed on the basis of a reaction model, that has been developed from the Post-Albers cycle. Analysis of the experimental data allows the determination of several rate constants of the pump cycle. Our conclusions may be summarized as follows: (a) binding of one Na+ ion at the cytoplasmic face is electrogenic. This Na+ ion is specifically bound to a neutral binding site with an affinity of 8 mM in the presence of 10 mM Mg2+. In the absence of divalent cations, the intrinsic binding affinity was found to be 0.7 mM. (b) The analysis of fluorescence experiments with the cardiotonic steroid strophanthidin indicates that the 5-iodoacetamidofluorescein label monitors the conformational transition (Na3)E1-P-->P-E2(Na2), which is accompanied by the release of one Na+ ion. 5-IAF does not respond to the release of the subsequent two Na+ ions, which can be monitored by the RH 421 dye. These experiments indicate further that the conformational transition E1P-->P-E2 is the rate limiting process of the Na+ translocation. The corresponding rate constant was determined to be 22 s-1 at 20 degrees C. From competition experiments with cardiotonic steroids, we estimated that the remaining 2 Na+ ions are released subsequently with a rate constant of at least 5,000 s-1 from their negatively charged binding sites. (c) Comparing the fluorescence experiments with electric current transients, which were performed at various Na concentrations in the absence and presence of strophanthidin, we found that the transition (Na3).E1-P-->P-E2.(Na2) is the major charge translocating step in the reaction sequence Na3.E1-->(Na3).E1-P-->P-E2.(Na2)-->P-E2. The subsequent release of 2 Na+ ions contributed less than 25% to the total electric current transient. (d) The well known antagonism between cardiotonic steroids and K+ binding can be explained by a kinetic model. A quantitative description has been obtained under the assumption that these inhibitors bind only to the states P-E2(Na2) and P-E2(K2).(ABSTRACT TRUNCATED AT 400 WORDS)

Spontaneous excitation of an accelerated atom: The contributions of vacuum fluctuations and radiation reaction

Abstract: We consider an atom in interaction with a massless scalar quantum field. We discuss the structure of the rate of variation of the atomic energy for an arbitrary stationary motion of the atom through the quantum vacuum. Our main intention is to identify and to analyze quantitatively the distinct contributions of vacuum fluctuations and radiation reaction to the spontaneous excitation of a uniformly accelerated atom in its ground state. This gives an understanding of the role of the different physical processes underlying the Unruh effect. The atom's evolution into equilibrium and the Einstein coefficients for spontaneous excitation and spontaneous emission are calculated.

Loss of spatial coherence by a single spontaneous emission.

Abstract: We have demonstrated the loss of transverse spatial coherence of an atomic wave function after a single spontaneous emission. ${\mathrm{He}}^{*}$ atoms were both diffracted and excited by a standing light wave with a variable period. After the interaction, the excited atoms decay by a single spontaneously emitted photon. By changing the period of the standing light wave, we have mapped the loss of spatial coherence as a function of the transverse coordinate. By detecting the emitted photon one could "erase" the position information available and recover the transverse coherence in a correlation experiment, or realize a Heisenberg microscope.

A survey of multiple contractions

Abstract: The AGM theory of belief contraction is extended tomultiple contraction, i.e. to contraction by a set of sentences rather than by a single sentence. There are two major variants: Inpackage contraction all the sentences must be removed from the belief set, whereas inchoice contraction it is sufficient that at least one of them is removed. Constructions of both types of multiple contraction are offered and axiomatically characterized. Neither package nor choice contraction can in general be reduced to contractions by single sentences; in the finite case choice contraction allows for reduction.

The Role of Jun Transcription Factor Expression and Phosphorylation in Neuronal Differentiation, Neuronal Cell Death, and Plastic Adaptations in Vivo

Abstract: 1. To investigate the role of the Jun transcription factors in neuronal differentiation, programmed neuronal cell death, and neuronal plasticity, we used phosphorothioate oligodeoxynucleotides (S-ODN) to inhibit selectively the expression of c-Jun, JunB, and JunD.

Trehalose-6-phosphate hydrolase of Escherichia coli.

Abstract: The disaccharide trehalose acts as an osmoprotectant as well as a carbon source in Escherichia coli. At high osmolarity of the growth medium, the cells synthesize large amounts of trehalose internally as an osmoprotectant. However, they can also degrade trehalose as the sole source of carbon under both high- and low-osmolarity growth conditions. The modes of trehalose utilization are different under the two conditions and have to be well regulated (W. Boos, U. Ehmann, H. Forkl, W. Klein, M. Rimmele, and P. Postma, J. Bacteriol. 172:3450-3461, 1990). At low osmolarity, trehalose is transported via a trehalose-specific enzyme II of the phosphotransferase system, encoded by treB. The trehalose-6-phosphate formed internally is hydrolyzed to glucose and glucose 6-phosphate by the key enzyme of the system, trehalose-6-phosphate hydrolase, encoded by treC. We have cloned treC, contained in an operon with treB as the promoter-proximal gene. We have overproduced and purified the treC gene product and identified it as a protein consisting of a single polypeptide with an apparent molecular weight of 62,000 as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The enzyme hydrolyzes trehalose-6-phosphate with a Km of 6 mM and a Vmax of at least 5.5 mumol of trehalose-6-phosphate hydrolyzed per min per mg of protein. The enzyme also very effectively hydrolyzes p-nitrophenyl-alpha-D-glucopyranoside, but it does not recognize trehalose, sucrose, maltose, isomaltose, or maltodextrins. treC was sequenced and found to encode a polypeptide with a calculated molecular weight of 63,781. The amino acid sequence deduced from the DNA sequence shows homology (50% identity) with those of oligo-1,6-glucosidases (sucrase-isomaltases) of Bacillus spp. but not with those of other disaccharide phosphate hydrolases. This report corrects our previous view on the function of the treC gene product as an amylotrehalase, which was based on the analysis of the metabolic products of trehalose metabolism in whole cells.