2,243 research outputs found
William R. Brinkley:A giant in biomedical research and public policy
Susan A. Gerbi, Robert E. Palazzo, William C. Earnshaw, and William T. Schrader discuss the life and achievements of William R. Brinkley, who passed away on November 10, 2020
Inducible DNA breaks in Ig S regions are dependent on AID and UNG
Class switch recombination (CSR) occurs by an intrachromosomal deletion whereby the IgM constant region gene (Cμ) is replaced by a downstream constant region gene. This unique recombination event involves formation of double-strand breaks (DSBs) in immunoglobulin switch (S) regions, and requires activation-induced cytidine deaminase (AID), which converts cytosines to uracils. Repair of the uracils is proposed to lead to DNA breaks required for recombination. Uracil DNA glycosylase (UNG) is required for most CSR activity although its role is disputed. Here we use ligation-mediated PCR to detect DSBs in S regions in splenic B cells undergoing CSR. We find that the kinetics of DSB induction corresponds with AID expression, and that DSBs are AID- and UNG-dependent and occur preferentially at G:C basepairs in WRC/GYW AID hotspots. Our results indicate that AID attacks cytosines on both DNA strands, and staggered breaks are processed to blunt DSBs at the initiating ss break sites. We propose a model to explain the types of end-processing events observed
Computing the local pressure in molecular dynamics simulations
Computer simulations of inhomogeneous soft matter systems often require
accurate methods for computing the local pressure. We present a simple
derivation, based on the virial relation, of two equivalent expressions for the
local (atomistic) pressure in a molecular dynamics simulation. One of these
expressions, previously derived by other authors via a different route,
involves summation over interactions between particles within the region of
interest; the other involves summation over interactions across the boundary of
the region of interest. We illustrate our derivation using simulations of a
simple osmotic system; both expressions produce accurate results even when the
region of interest over which the pressure is measured is very small.Comment: 11 pages, 4 figure
Positronic lithium, an electronically stable Li-e ground state
Calculations of the positron-Li system were performed using the Stochastic
Variational Method and yielded a minimum energy of -7.53208 Hartree for the L=0
ground state. Unlike previous calculations of this system, the system was found
to be stable against dissociation into the Ps + Li channel with a binding
energy of 0.00217 Hartree and is therefore electronically stable. This is the
first instance of a rigorous calculation predicting that it is possible to
combine a positron with a neutral atom and form an electronically stable bound
state.Comment: 11 pages, 2 tables. To be published in Phys.Rev.Let
Molecular Tweezers with Varying Anions: A Comparative Study
Selective binding of the phosphate-substituted molecular tweezer 1a to protein lysine residues was suggested to explain the inhibition of certain enzymes and the aberrant aggregation of amyloid petide Aβ42 or α-synuclein, which are assumed to be responsible for Alzheimer’s and Parkinson’s disease, respectively. In this work we systematically investigated the binding of four water-soluble tweezers 1a−d (substituted by phosphate, methanephosphonate, sulfate, or O-methylenecarboxylate groups) to amino acids and peptides containing lysine or arginine residues by using fluorescence spectroscopy, NMR spectroscopy, and isothermal titration calorimetry (ITC). The comparison of the experimental results with theoretical data obtained by a combination of QM/MM and ab initio 1H NMR shift calculations provides clear evidence that the tweezers 1a−c bind the amino acid or peptide guest molecules by threading the lysine or arginine side chain through the tweezers’ cavity, whereas in the case of 1d the guest molecule is preferentially positioned outside the tweezer’s cavity. Attractive ionic, CH-π, and hydrophobic interactions are here the major binding forces. The combination of experiment and theory provides deep insight into the host−guest binding modes, a prerequisite to understanding the exciting influence of these tweezers on the aggregation of proteins and the activity of enzymes
Positron and positronium affinities in the work-formalism Hartree-Fock approximation
Positron binding to anions is investigated within the work formalism proposed
by Harbola and Sahni for the halide anions and the systems Li^- through O^-
excluding Be^- and N^-. The toal ground-state energies of the anion-positron
bound systems are empirically found to be an upper bound to the Hartree-Fock
energies. The computed expectation values as well as positron and positronium
affinities are in good agreement with their restricted Hartree-Fock
counterparts. Binding of a positron to neutral species is also investigated
using an iterative method.Comment: 12 pages, to appear in Physical Review
Existence criteria for stabilization from the scaling behaviour of ionization probabilities
We provide a systematic derivation of the scaling behaviour of various
quantities and establish in particular the scale invariance of the ionization
probability. We discuss the gauge invariance of the scaling properties and the
manner in which they can be exploited as consistency check in explicit
analytical expressions, in perturbation theory, in the Kramers-Henneberger and
Floquet approximation, in upper and lower bound estimates and fully numerical
solutions of the time dependent Schroedinger equation. The scaling invariance
leads to a differential equation which has to be satisfied by the ionization
probability and which yields an alternative criterium for the existence of
atomic bound state stabilization.Comment: 12 pages of Latex, one figur
Power Spectrum Analysis of Physikalisch-Technische Bundesanstalt Decay-Rate Data: Evidence for Solar Rotational Modulation
Evidence for an anomalous annual periodicity in certain nuclear decay data
has led to speculation concerning a possible solar influence on nuclear
processes. We have recently analyzed data concerning the decay rates of Cl-36
and Si-32, acquired at the Brookhaven National Laboratory (BNL), to search for
evidence that might be indicative of a process involving solar rotation.
Smoothing of the power spectrum by weighted-running-mean analysis leads to a
significant peak at frequency 11.18/yr, which is lower than the equatorial
synodic rotation rates of the convection and radiative zones. This article
concerns measurements of the decay rates of Ra-226 acquired at the
Physikalisch-Technische Bundesanstalt (PTB) in Germany. We find that a similar
(but not identical) analysis yields a significant peak in the PTB dataset at
frequency 11.21/yr, and a peak in the BNL dataset at 11.25/yr. The change in
the BNL result is not significant since the uncertainties in the BNL and PTB
analyses are estimated to be 0.13/yr and 0.07/yr, respectively. Combining the
two running means by forming the joint power statistic leads to a highly
significant peak at frequency 11.23/yr. We comment briefly on the possible
implications of these results for solar physics and for particle physics.Comment: 15 pages, 13 figure
Brownian Motions on Metric Graphs
Brownian motions on a metric graph are defined. Their generators are
characterized as Laplace operators subject to Wentzell boundary at every
vertex. Conversely, given a set of Wentzell boundary conditions at the vertices
of a metric graph, a Brownian motion is constructed pathwise on this graph so
that its generator satisfies the given boundary conditions.Comment: 43 pages, 7 figures. 2nd revision of our article 1102.4937: The
introduction has been modified, several references were added. This article
will appear in the special issue of Journal of Mathematical Physics
celebrating Elliott Lieb's 80th birthda
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