1,924 research outputs found
Site-specific incorporation of phosphotyrosine using an expanded genetic code.
Access to phosphoproteins with stoichiometric and site-specific phosphorylation status is key to understanding the role of protein phosphorylation. Here we report an efficient method to generate pure, active phosphotyrosine-containing proteins by genetically encoding a stable phosphotyrosine analog that is convertible to native phosphotyrosine. We demonstrate its general compatibility with proteins of various sizes, phosphotyrosine sites and functions, and reveal a possible role of tyrosine phosphorylation in negative regulation of ubiquitination
Pharmacological screening using an FXN-EGFP cellular genomic reporter assay for the therapy of Friedreich ataxia
Copyright @ 2013 Li et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Friedreich ataxia (FRDA) is an autosomal recessive disorder characterized by neurodegeneration and cardiomyopathy. The presence of a GAA trinucleotide repeat expansion in the first intron of the FXN gene results in the inhibition of gene expression and an insufficiency of the mitochondrial protein frataxin. There is a correlation between expansion length, the amount of residual frataxin and the severity of disease. As the coding sequence is unaltered, pharmacological up-regulation of FXN expression may restore frataxin to therapeutic levels. To facilitate screening of compounds that modulate FXN expression in a physiologically relevant manner, we established a cellular genomic reporter assay consisting of a stable human cell line containing an FXN-EGFP fusion construct, in which the EGFP gene is fused in-frame with the entire normal human FXN gene present on a BAC clone. The cell line was used to establish a fluorometric cellular assay for use in high throughput screening (HTS) procedures. A small chemical library containing FDA-approved compounds and natural extracts was screened and analyzed. Compound hits identified by HTS were further evaluated by flow cytometry in the cellular genomic reporter assay. The effects on FXN mRNA and frataxin protein levels were measured in lymphoblast and fibroblast cell lines derived from individuals with FRDA and in a humanized GAA repeat expansion mouse model of FRDA. Compounds that were established to increase FXN gene expression and frataxin levels included several anti-cancer agents, the iron-chelator deferiprone and the phytoalexin resveratrol.Muscular Dystrophy Association (USA), the National Health and Medical Research Council (Australia), the Friedreich’s Ataxia Research Alliance (USA), the Brockhoff Foundation (Australia), the Friedreich Ataxia Research Association (Australasia), Seek A Miracle (USA) and the Victorian Government’s Operational Infrastructure Support Program
Measurement of Beam-Spin Asymmetries for Deep Inelastic Electroproduction
We report the first evidence for a non-zero beam-spin azimuthal asymmetry in
the electroproduction of positive pions in the deep-inelastic region. Data have
been obtained using a polarized electron beam of 4.3 GeV with the CLAS detector
at the Thomas Jefferson National Accelerator Facility (JLab). The amplitude of
the modulation increases with the momentum of the pion relative to
the virtual photon, , with an average amplitude of for range.Comment: 5 pages, RevTEX4, 3 figures, 2 table
Measurement of the Polarized Structure Function for in the Resonance Region
The polarized longitudinal-transverse structure function
has been measured in the resonance region at and 0.65
GeV. Data for the reaction were taken at Jefferson Lab
with the CEBAF Large Acceptance Spectrometer (CLAS) using longitudinally
polarized electrons at an energy of 1.515 GeV. For the first time a complete
angular distribution was measured, permitting the separation of different
non-resonant amplitudes using a partial wave analysis. Comparison with previous
beam asymmetry measurements at MAMI indicate a deviation from the predicted
dependence of using recent phenomenological
models.Comment: 5 pages, LaTex, 4 eps figures: to be published in PRC/Rapid
Communications. Version 2 has revised Q^2 analysi
Two-Nucleon Momentum Distributions Measured in 3He(e,e'pp)n
We have measured the 3He(e,e'pp)n reaction at 2.2 GeV over a wide kinematic
range. The kinetic energy distribution for `fast' nucleons (p > 250 MeV/c)
peaks where two nucleons each have 20% or less, and the third nucleon has most
of the transferred energy. These fast pp and pn pairs are back-to-back with
little momentum along the three-momentum transfer, indicating that they are
spectators. Experimental and theoretical evidence indicates that we have
measured distorted two-nucleon momentum distributions by striking the third
nucleon and detecting the spectator correlated pair.Comment: 6 pages, 5 figures, submitted to PR
Survey of A_LT' asymmetries in semi-exclusive electron scattering on He4 and C12
Single spin azimuthal asymmetries A_LT' were measured at Jefferson Lab using
2.2 and 4.4 GeV longitudinally polarized electrons incident on He4 and C12
targets in the CLAS detector. A_LT' is related to the imaginary part of the
longitudinal-transverse interference and in quasifree nucleon knockout it
provides an unambiguous signature for final state interactions (FSI).
Experimental values of A_LT' were found to be below 5%, typically |A_LT'| < 3%
for data with good statistical precision. Optical Model in Eikonal
Approximation (OMEA) and Relativistic Multiple-Scattering Glauber Approximation
(RMSGA) calculations are shown to be consistent with the measured asymmetries.Comment: 9 pages, 5 figure
Onset of asymptotic scaling in deuteron photodisintegration
We investigate the transition from the nucleon-meson to quark-gluon
description of the strong interaction using the photon energy dependence of the
differential cross section for photon energies above 0.5 GeV and
center-of-mass proton angles between and . A possible
signature for this transition is the onset of cross section scaling
with the total energy squared, , at some proton transverse momentum, .
The results show that the scaling has been reached for proton transverse
momentum above about 1.1 GeV/c. This may indicate that the quark-gluon regime
is reached above this momentum.Comment: Accepted by PRL; 5 pages, 2 figure
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