1,210 research outputs found
Synthesis of new spin labels for Cu-free click conjugation
New pyrroline nitroxides attached to a terminal acetylenic sulfone, a dibenzocyclooctyne or a cyclooctyne
carboxylic acid were synthesized and tested in Cu-free click reactions to conjugate these new spin
labels with 4-azido-TEMPO, azidophenylalanine and an azidophenylalanine-containing protein
Coincidence between transcriptome analyses on different microarray platforms using a parametric framework
A parametric framework for the analysis of transcriptome data is demonstrated to yield coincident results when applied to data acquired using two different microarray platforms. Discrepancies among transcriptome studies are frequently reported, casting doubt on the reliability of collected data. The inconsistency among observations can be largely attributed to differences among the analytical frameworks employed for data analysis. The existing frameworks normalizes data against a standard determined from the data to be analyzed. In the present study, a parametric framework based on a strict model for normalization is applied to data acquired using an in-house printed chip and GeneChip. The framework is based on a common statistical characteristic of microarray data, and each data is normalized on the basis of a linear relationship with this model. In the proposed framework, the expressional changes observed and genes selected are coincident between platforms, achieving superior universality of data compared to other methods
Protonation state of glutamate 73 regulates the formation of a specific dimeric association of mVDAC1.
The voltage-dependent anion channel (VDAC) is the most abundant protein in the outer mitochondrial membrane and constitutes the primary pathway for the exchange of ions and metabolites between the cytosol and the mitochondria. There is accumulating evidence supporting VDAC's role in mitochondrial metabolic regulation and apoptosis, where VDAC oligomerization has been implicated with these processes. Herein, we report a specific pH-dependent dimerization of murine VDAC1 (mVDAC1) identified by double electron-electron resonance and native mass spectrometry. Intermolecular distances on four singly spin-labeled mVDAC1 mutants were used to generate a model of the low-pH dimer, establishing the presence of residue E73 at the interface. This dimer arrangement is different from any oligomeric state previously described, and it forms as a steep function of pH with an apparent pKa of 7.4. Moreover, the monomer-dimer equilibrium affinity constant was determined using native MS, revealing a nearly eightfold enhancement in dimerization affinity at low pH. Mutation of E73 to either alanine or glutamine severely reduces oligomerization, demonstrating the role of protonated E73 in enhancing dimer formation. Based on these results, and the known importance of E73 in VDAC physiology, VDAC dimerization likely plays a significant role in mitochondrial metabolic regulation and apoptosis in response to cytosolic acidification during cellular stress
Large Fluctuations and Fixation in Evolutionary Games
We study large fluctuations in evolutionary games belonging to the
coordination and anti-coordination classes. The dynamics of these games,
modeling cooperation dilemmas, is characterized by a coexistence fixed point
separating two absorbing states. We are particularly interested in the problem
of fixation that refers to the possibility that a few mutants take over the
entire population. Here, the fixation phenomenon is induced by large
fluctuations and is investigated by a semi-classical WKB
(Wentzel-Kramers-Brillouin) theory generalized to treat stochastic systems
possessing multiple absorbing states. Importantly, this method allows us to
analyze the combined influence of selection and random fluctuations on the
evolutionary dynamics \textit{beyond} the weak selection limit often considered
in previous works. We accurately compute, including pre-exponential factors,
the probability distribution function in the long-lived coexistence state and
the mean fixation time necessary for a few mutants to take over the entire
population in anti-coordination games, and also the fixation probability in the
coordination class. Our analytical results compare excellently with extensive
numerical simulations. Furthermore, we demonstrate that our treatment is
superior to the Fokker-Planck approximation when the selection intensity is
finite.Comment: 17 pages, 10 figures, to appear in JSTA
On the Absorption of X-rays in the Interstellar Medium
We present an improved model for the absorption of X-rays in the ISM intended
for use with data from future X-ray missions with larger effective areas and
increased energy resolution such as Chandra and XMM, in the energy range above
100eV. Compared to previous work, our formalism includes recent updates to the
photoionization cross section and revised abundances of the interstellar
medium, as well as a treatment of interstellar grains and the H2molecule. We
review the theoretical and observational motivations behind these updates and
provide a subroutine for the X-ray spectral analysis program XSPEC that
incorporates our model.Comment: ApJ, in press, for associated software see
http://astro.uni-tuebingen.de/nh
Measurement of the Electric and Magnetic Polarizabilities of the Proton
The Compton scattering cross section on the proton has been measured at
laboratory angles of 90 and 135 using tagged photons in the
energy range 70--100 MeV and simultaneously using untagged photons in the range
100--148~MeV. With the aid of dispersion relations, these cross sections were
used to extract the electric and magnetic polarizabilities, and
respectively, of the proton. We find
in agreement with a model-independent dispersion sum rule, and
where the errors shown are statistical, systematic, and model-dependent,
respectively. A comparison with previous experiments is given and global values
for the polarizabilities are extracted.Comment: 35 pages, 11 PostScript figures, uses RevTex 3.
Robustness Against Extinction by Stochastic Sex Determination in Small Populations
Sexually reproducing populations with small number of individuals may go
extinct by stochastic fluctuations in sex determination, causing all their
members to become male or female in a generation. In this work we calculate the
time to extinction of isolated populations with fixed number of individuals
that are updated according to the Moran birth and death process. At each time
step, one individual is randomly selected and replaced by its offspring
resulting from mating with another individual of opposite sex; the offspring
can be male or female with equal probability. A set of time steps is called
a generation, the average time it takes for the entire population to be
replaced. The number k of females fluctuates in time, similarly to a random
walk, and extinction, which is the only asymptotic possibility, occurs when k=0
or k=N. We show that it takes only one generation for an arbitrary initial
distribution of males and females to approach the binomial distribution. This
distribution, however, is unstable and the population eventually goes extinct
in 2^N/N generations. We also discuss the robustness of these results against
bias in the determination of the sex of the offspring, a characteristic
promoted by infection by the bacteria Wolbachia in some arthropod species or by
temperature in reptiles.Comment: 17 pages, 2 figure
The Moran model as a dynamical process on networks and its implications for neutral speciation
In genetics the Moran model describes the neutral evolution of a bi-allelic
gene in a population of haploid individuals subjected to mutations. We show in
this paper that this model can be mapped into an influence dynamical process on
networks subjected to external influences. The panmictic case considered by
Moran corresponds to fully connected networks and can be completely solved in
terms of hypergeometric functions. Other types of networks correspond to
structured populations, for which approximate solutions are also available.
This new approach to the classic Moran model leads to a relation between
regular networks based on spatial grids and the mechanism of isolation by
distance. We discuss the consequences of this connection for topopatric
speciation and the theory of neutral speciation and biodiversity. We show that
the effect of mutations in structured populations, where individuals can mate
only with neighbors, is greatly enhanced with respect to the panmictic case. If
mating is further constrained by genetic proximity between individuals, a
balance of opposing tendencies take place: increasing diversity promoted by
enhanced effective mutations versus decreasing diversity promoted by similarity
between mates. Stabilization occurs with speciation via pattern formation. We
derive an explicit relation involving the parameters characterizing the
population that indicates when speciation is possible.Comment: Improved analytical treatment of speciatio
A multi-detector array for high energy nuclear e+e- pair spectrosocopy
A multi-detector array has been constructed for the simultaneous measurement
of energy- and angular correlation of electron-positron pairs produced in
internal pair conversion (IPC) of nuclear transitions up to 18 MeV. The
response functions of the individual detectors have been measured with
mono-energetic beams of electrons. Experimental results obtained with 1.6 MeV
protons on targets containing B and F show clear IPC over a wide
angular range. A comparison with GEANT simulations demonstrates that angular
correlations of pairs of transitions in the energy range between 6 and
18 MeV can be determined with sufficient resolution and efficiency to search
for deviations from IPC due to the creation and subsequent decay into
of a hypothetical short-lived neutral boson.Comment: 20 pages, 8 figure
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