61,873 research outputs found
CadC-mediated activation of the cadBA promoter in Escherichia coli
The transcriptional activator CadC in Escherichia coli, a member of the ToxR-like proteins, activates transcription of the cadBA operon encoding the lysine decarboxylase CadA and the lysine-cadaverine antiporter CadB. cadBA is induced under conditions of acidic external pH and exogenous lysine; anoxic conditions raise the expression level up to 10 times. To characterize the binding mechanism of CadC, procedures for the purification of this membrane-integrated protein and its reconstitution into proteoliposomes were established. The binding sites of CadC upstream of the cadBA promoter region were determined by in vitro DNaseI protection analysis. Two regions were protected during DNaseI digestion, one from - 144 to - 112 bp, designated Cad1, and another one from - 89 to - 59 bp, designated Cad2. Binding of purified CadC to Cad1 and Cad2 was further characterized by DNA-binding assays, indicating that CadC was able to bind to both DNA fragments. Genetic analysis with promoter-lacZ fusions confirmed that both sites, Cad1 and Cad2, are essential for activation of cadBA transcription. Moreover, these experiments revealed that binding of H-NS upstream of the CadC-binding sites is necessary for repression of cadBA expression at neutral pH and under aerobic conditions. Based on these results, a model for transcriptional regulation of the cadBA operon is proposed, according to which H-NS is involved in the formation of a repression complex under non-inducing conditions. This complex is dissolved by binding of CadC to Cad1 under inducing conditions. Upon binding of CadC to Cad2 cadBA expression is activated. Copyright (C) 2005 S. Karger AG, Basel
Form Invariance of the Neutrino Mass Matrix
Consider the most general Majorana neutrino mass matrix . Motivated by present neutrino-oscillation data, much theoretical effort is
directed at reducing it to a specific texture in terms of a small number of
parameters. This procedure is often {\it ad hoc}. I propose instead that for
any one may choose, it should satisfy the condition , where is a specific unitary matrix such that
represents a well-defined discrete symmetry in the basis,
being a particular integer not necessarily equal to one. I illustrate this
idea with a number of examples, including the realistic case of an inverted
hierarchy of neutrino masses.Comment: Version to appear in PR
Zigzag Filamentary Theory of Broken Symmetry of Neutron and Infrared Vibronic Spectra of YBa2Cu3O(6+x)
Filamentary high-temperature superconductivity (HTSC) theory differs
fundamentally from continuous HTSC theories because it emphasizes
self-organized, discrete dopant networks and does not make the effective medium
approximation (EMA). Analysis of neutron and infrared (especially with c-axis
polarization) vibrational spectra, primarily for YBa2Cu3O(6+x), within the
filamentary framework, shows that the observed vibronic anomalies near 400 cm-1
(50 meV) are associated with curvilinear filamentary paths. these paths pass
through cuprate chains and planes, as well as resonant tunneling centers in the
BaO layers. The analysis and the data confirm earlier filamentary structural
models containing ferroelastic domains of 3-4 nm in the CuO2 planes; it is
these nanodomains that are responsible for the discrete glassy nature of both
electronic and vibronic properties. Chemical trends in vibronic energies and
oscillator strengths, both for neutron and photon scattering, that were
anomalous in continuum models, are readily explained by the filamentary model.Comment: 45 pages, 17 figures, PD
Semiclassical approach to Bose-Einstein condensates in a triple well potential
We present a new approach for the analysis of Bose-Einstein condensates in a
few mode approximation. This method has already been used to successfully
analyze the vibrational modes in various molecular systems and offers a new
perspective on the dynamics in many particle bosonic systems. We discuss a
system consisting of a Bose-Einstein condensate in a triple well potential.
Such systems correspond to classical Hamiltonian systems with three degrees of
freedom. The semiclassical approach allows a simple visualization of the
eigenstates of the quantum system referring to the underlying classical
dynamics. From this classification we can read off the dynamical properties of
the eigenstates such as particle exchange between the wells and entanglement
without further calculations. In addition, this approach offers new insights
into the validity of the mean-field description of the many particle system by
the Gross-Pitaevskii equation, since we make use of exactly this correspondence
in our semiclassical analysis. We choose a three mode system in order to
visualize it easily and, moreover, to have a sufficiently interesting
structure, although the method can also be extended to higher dimensional
systems.Comment: 15 pages, 15 figure
The Diffractive Interactions Working Group Summary
Diffractive interactions represent a lively domain of investigations, as
confirmed by the progresses reported during the conference. We summarize the
diffractive interactions session and put the new experimental data (section 1),
developments in modeling diffraction (section 2) and the theoretical relations
with Quantum Chromodynamics (section 3) in perspective.Comment: Summary report at DIS200
Extraction of information about periodic orbits from scattering functions
As a contribution to the inverse scattering problem for classical chaotic
systems, we show that one can select sequences of intervals of continuity, each
of which yields the information about period, eigenvalue and symmetry of one
unstable periodic orbit.Comment: LaTeX, 13 pages (includes 5 eps-figures
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