GlnK-abhängige Signaltransduktion in Corynebacterium glutamicum

Das Gram-positive Bodenbakterium Corynebacterium glutamicum gehört phylogenetisch zu den Mycolsäure haltigen Actinomyceten und hat seit seiner Entdeckung in den fünfziger Jahren als natürlicher Glutamatproduzent eine große biotechnologische Bedeutung erlangt. Neben L-Glutamat und L-Lysin wird C. glutamicum zunehmend für fermentative Produktionsprozesse anderer Aminosäuren sowie für die Herstellung von Nukleotiden und Vitaminen genutzt. Stickstoff ist für C. glutamicum zur Biosynthese aller Aminosäuren von essenzieller Bedeutung. Um eine unnötige Verschwendung von Energie und Nährstoffreserven zu vermeiden, besitzt dieser Organismus Regulationsmechanismen, die die Aufnahme und Assimilation von Stickstoff unter verschiedenen Bedingungen sowohl auf der Aktivitätsebene als auch auf der Genexpressionsebene kontrollieren. Diese werden mit dem Begriff "Stickstoffkontrolle" bezeichnet. Ziel dieser Arbeit war die Charakerisierung der GlnK-abhängigen Signaltransduktion in C. glutamicum. Zum Einen wurde die zentrale Stellung des PII-Signaltransduktionsproteins GlnK innerhalb der Stickstoffregulation untersucht und bestätigt. Zum Anderen konnte die GlnK-abhängige Signaltransduktion im Hinblick auf die Signalaufnahme und Signalweiterleitung charakterisiert werden. So ließ sich zeigen, dass das GlnK-Protein in C. glutamicum als Trimer aktiv ist und als Antwort auf Stickstoffmangel von GlnD an allen drei Untereinheiten adenylyliert wird. In der modifzierten Form interagiert GlnK mit dem globalen Repressor der Stickstoffkontrolle AmtR. Infolgedessen wird die Expression stickstoffregulierter Gene induziert. Verbessert sich die Stickstoffversorgung der Zelle, wird GlnK von GlnD demodifiziert und interagiert mit dem Ammoniumtransporter AmtB. Eine Verschiebung der Lokalisation von GlnK - vom Cytoplasma zur Membran - hat außerdem den Abbau des Proteins zur Folge, der von den Clp-Protease-Komplexen ClpCP und ClpXP sowie von der membranständigen Protease FtsH beeinflusst wird. Die Ergebnisse aus Experimenten zur Signalaufnahme und -weiterleitung lassen vermuten, dass der Marker des Stickstoffstatus nicht Glutamin sondern Ammonium ist. Die Frage, wie C. glutamicum den Stickstoffgehalt des Mediums wahrnimmt, konnte nicht abschließend geklärt werden. Neben einer GlnK-abhängigen Signaltransduktion scheint es in C. glutamicum zusätzlich einen von GlnK unabhängigen Signalweg zu geben, in dem die ATase den Stickstoffstatus der Zelle wahrnimmt und die Glutaminsynthetase dementsprechend aktiviert bzw. deaktiviert

Promjena pulsa kod kratkotrajnih mentalnih radova

Veränderungen der Pulsfrequenz bei einfachen kurzzeittigen Konzen-trationsleitungen wurden an 15 Mädchen, 15 Jungen und 15 Erwachsenen in insgesamt 90 Einzelversuchen untersucht. Die Beobachtung anderer Autoren über eine Pulsbeschleunigung bei einfach strukturierter geistiger\u27 Arbeit konnte bestätigt werden.Na 15 mladića, 15 djevojaka i 15 odraslih mjerili su autori promjene pulsa do kojih dolazi u toku kratkotrajnog računanja. Potvrdili su opažanja nekih drugih autora, da u toku takvog rada dolazi do ubrzanja pulsa. Ako se u toku rada uvedu kratke pauze, to dovodi do izvjesnog fiziološkog oporavka, ali u radnom učinku nisu opažene promjene. Izvjesne razlike opažene su među dječacima i djevojčicama, kao i između mladih i starijih ispitanika. Nije nađena nikakva zavisnost između radnog pulsa i radnog učinka u računanju

Specific Heat of Liquid Helium in Zero Gravity very near the Lambda Point

We report the details and revised analysis of an experiment to measure the specific heat of helium with subnanokelvin temperature resolution near the lambda point. The measurements were made at the vapor pressure spanning the region from 22 mK below the superfluid transition to 4 uK above. The experiment was performed in earth orbit to reduce the rounding of the transition caused by gravitationally induced pressure gradients on earth. Specific heat measurements were made deep in the asymptotic region to within 2 nK of the transition. No evidence of rounding was found to this resolution. The optimum value of the critical exponent describing the specific heat singularity was found to be a = -0.0127+ - 0.0003. This is bracketed by two recent estimates based on renormalization group techniques, but is slightly outside the range of the error of the most recent result. The ratio of the coefficients of the leading order singularity on the two sides of the transition is A+/A- =1.053+ - 0.002, which agrees well with a recent estimate. By combining the specific heat and superfluid density exponents a test of the Josephson scaling relation can be made. Excellent agreement is found based on high precision measurements of the superfluid density made elsewhere. These results represent the most precise tests of theoretical predictions for critical phenomena to date.Comment: 27 Pages, 20 Figure

Minimal renormalization without epsilon-expansion: Amplitude functions in three dimensions below T_c

Massive field theory at fixed dimension d<4 is combined with the minimal subtraction scheme to calculate the amplitude functions of thermodynamic quantities for the O(n) symmetric phi^4 model below T_c in two-loop order. Goldstone singularities arising at an intermediate stage in the calculation of O(n) symmetric quantities are shown to cancel among themselves leaving a finite result in the limit of zero external field. From the free energy we calculate the amplitude functions in zero field for the order parameter, specific heat and helicity modulus (superfluid density) in three dimensions. We also calculate the q^2 part of the inverse of the wavenumber-dependent transverse susceptibility chi_T(q) which provides an independent check of our result for the helicity modulus. The two-loop contributions to the superfluid density and specific heat below T_c turn out to be comparable in magnitude to the one-loop contributions, indicating the necessity of higher-order calculations and Pade-Borel type resummations.Comment: 41 pages, LaTeX, 8 PostScript figures, submitted to NPB [FS

Two-Loop Effective Potential of O(N)-Symmetric Scalar QED in 4-epsilon Dimensions

The effective potential of scalar QED is computed analytically up to two loops in the Landau gauge. The result is given in 4-epsilon dimensions using minimal subtraction and epsilon-expansions. In three dimensions, our calculation is intended to help throw light on unsolved problems of the superconducting phase transition, where critical exponents and the position of the tricritical point have not yet found a satisfactory explanation within the renormalization group approach.Comment: Author Information under http://www.physik.fu-berlin.de/~kleinert/institution.html . Latest update of paper (including all PS fonts) at http://www.physik.fu-berlin.de/~kleinert/32

Nitrogen regulation of protein–protein interactions and transcript levels of GlnK PII regulator and AmtB ammonium transporter homologs in Archaea

Gene homologs of GlnK PII regulators and AmtB-type ammonium transporters are often paired on prokaryotic genomes, suggesting these proteins share an ancient functional relationship. Here, we demonstrate for the first time in Archaea that GlnK associates with AmtB in membrane fractions after ammonium shock, thus, providing a further insight into GlnK-AmtB as an ancient nitrogen sensor pair. For this work, Haloferax mediterranei was advanced for study through the generation of a pyrE2-based counterselection system that was used for targeted gene deletion and expression of Flag-tagged proteins from their native promoters. AmtB1-Flag was detected in membrane fractions of cells grown on nitrate and was found to coimmunoprecipitate with GlnK after ammonium shock. Thus, in analogy to bacteria, the archaeal GlnK PII may block the AmtB1 ammonium transporter under nitrogen-rich conditions. In addition to this regulated protein–protein interaction, the archaeal amtB-glnK gene pairs were found to be highly regulated by nitrogen availability with transcript levels high under conditions of nitrogen limitation and low during nitrogen excess. While transcript levels of glnK-amtB are similarly regulated by nitrogen availability in bacteria, transcriptional regulators of the bacterial glnK promoter including activation by the two-component signal transduction proteins NtrC (GlnG, NRI) and NtrB (GlnL, NRII) and sigma factor σN (σ54) are not conserved in archaea suggesting a novel mechanism of transcriptional control

Minimal renormalization without \epsilon-expansion: Three-loop amplitude functions of the O(n) symmetric \phi^4 model in three dimensions below T_c

We present an analytic three-loop calculation for thermodynamic quantities of the O(n) symmetric \phi^4 theory below T_c within the minimal subtraction scheme at fixed dimension d=3. Goldstone singularities arising at an intermediate stage in the calculation of O(n) symmetric quantities cancel among themselves leaving a finite result in the limit of zero external field. From the free energy we calculate the three-loop terms of the amplitude functions f_phi, F+ and F- of the order parameter and the specific heat above and below T_c, respectively, without using the \epsilon=4-d expansion. A Borel resummation for the case n=2 yields resummed amplitude functions f_phi and F- that are slightly larger than the one-loop results. Accurate knowledge of these functions is needed for testing the renormalization-group prediction of critical-point universality along the \lambda-line of superfluid He(4). Combining the three-loop result for F- with a recent five-loop calculation of the additive renormalization constant of the specific heat yields excellent agreement between the calculated and measured universal amplitude ratio A+/A- of the specific heat of He(4). In addition we use our result for f_phi to calculate the universal combination R_C of the amplitudes of the order parameter, the susceptibility and the specific heat for n=2 and n=3. Our Borel-resummed three-loop result for R_C is significantly more accurate than the previous result obtained from the \epsilon-expansion up to O(\epsilon^2).Comment: 29 pages LaTeX including 3 PostScript figures, to appear in Nucl. Phys. B [FS] (1998

Five-loop additive renormalization in the phi^4 theory and amplitude functions of the minimally renormalized specific heat in three dimensions

We present an analytic five-loop calculation for the additive renormalization constant A(u,epsilon) and the associated renormalization-group function B(u) of the specific heat of the O(n) symmetric phi^4 theory within the minimal subtraction scheme. We show that this calculation does not require new five-loop integrations but can be performed on the basis of the previous five-loop calculation of the four-point vertex function combined with an appropriate identification of symmetry factors of vacuum diagrams. We also determine the amplitude functions of the specific heat in three dimensions for n=1,2,3 above T_c and for n=1 below T_c up to five-loop order. Accurate results are obtained from Borel resummations of B(u) for n=1,2,3 and of the amplitude functions for n=1. Previous conjectures regarding the smallness of the resummed higher-order contributions are confirmed. Borel resummed universal amplitude ratios A^+/A^- and a_c^+/a_c^- are calculated for n=1.Comment: 30 pages REVTeX, 3 PostScript figures, submitted to Phys. Rev.

Three-loop critical exponents, amplitude functions, and amplitude ratios from variational perturbation theory

We use variational perturbation theory to calculate various universal amplitude ratios above and below T_c in minimally subtracted phi^4-theory with N components in three dimensions. In order to best exhibit the method as a powerful alternative to Borel resummation techniques, we consider only to two- and three-loops expressions where our results are analytic expressions. For the critical exponents, we also extend existing analytic expressions for two loops to three loops.Comment: Author Information under http://www.physik.fu-berlin.de/~kleinert/institution.html . Latest update of paper (including all PS fonts) at http://www.physik.fu-berlin.de/~kleinert/kleiner_re318/preprint.htm

Critical behavior of the three-dimensional XY universality class

We improve the theoretical estimates of the critical exponents for the three-dimensional XY universality class. We find alpha=-0.0146(8), gamma=1.3177(5), nu=0.67155(27), eta=0.0380(4), beta=0.3485(2), and delta=4.780(2). We observe a discrepancy with the most recent experimental estimate of alpha; this discrepancy calls for further theoretical and experimental investigations. Our results are obtained by combining Monte Carlo simulations based on finite-size scaling methods, and high-temperature expansions. Two improved models (with suppressed leading scaling corrections) are selected by Monte Carlo computation. The critical exponents are computed from high-temperature expansions specialized to these improved models. By the same technique we determine the coefficients of the small-magnetization expansion of the equation of state. This expansion is extended analytically by means of approximate parametric representations, obtaining the equation of state in the whole critical region. We also determine the specific-heat amplitude ratio.Comment: 61 pages, 3 figures, RevTe