15,112 research outputs found
Human complement factor H
We isolated cDNA clones coding for the functionally important tryptic N-terminal38-
kDa fragment of human complement control protein factor H using polyclonal and
monoclonal antibodies to screen a human liver cDNA library cloned in a bacterial
expression vector, PEX-1. By testing the reactivity of antibodies specific for the
recombinant proteins produced by individual clones with proteolytic fragments of
serum H the exact position of these cDNA clones within H was mapped. One clone,
H-19, coding for the 38-kDa fragment of H was sequenced and found to code for 289
amino acids derived from the 38-kDa N-terminal fragment as well as for the first 108
amino acids belonging to the complementary 142-kDa tryptic fragment. The derived
protein sequence could be arranged in 6 highly homologous repeats of about 60 amino
acids each, the homology between the repeats being determined by the characteristic
position of cysteine, proline, glycine, tyrosine and tryptophane residues. The region
coding for the epitope recognized by one of our monoclonal antibodies was localized
by subcloning restriction fragments of H-19 into the expression plasmid and testing
for the expression of this epitope
C-Terminal truncation of NR2A subunits impairs synaptic but not extrasynaptic localization of NMDA receptors
NMDA receptors interact via the extended intracellular C-terminal domain of the NR2 subunits with constituents of the postsynaptic density for purposes of retention, clustering, and functional regulation at central excitatory synapses. To examine the role of the C-terminal domain of NR2A in the synaptic localization and function of NR2A-containing NMDA receptors in hippocampal Schaffer collateral–CA1 pyramidal cell synapses, we analyzed mice which express NR2A only in its C-terminally truncated form. In CA1 cell somata, the levels, activation, and deactivation kinetics of extrasynaptic NMDA receptor channels were comparable in wild-type and mutant NR2A^(ΔC/ΔC) mice. At CA1 cell synapses, however, the truncated receptors were less concentrated than their full-length counterparts, as indicated by immunodetection in cultured neurons, synaptosomes, and postsynaptic densities. In the mutant, the NMDA component of evoked EPSCs was reduced in a developmentally progressing manner and was even more reduced in miniature EPSCs (mEPSCs) elicited by spontaneous glutamate release. Moreover, pharmacologically isolated NMDA currents evoked by synaptic stimulation had longer latencies and displayed slower rise and decay times, even in the presence of an NR2B-specific antagonist. These data strongly suggest that the C-terminal domain of NR2A subunits is important for the precise synaptic arrangement of NMDA receptors
Evidence for a parsec scale X-ray jet from the accreting neutron star Circinus X-1
We analyzed the zero-order image of a 50 ks Chandra gratings observation of
Circinus X-1, taken in 2005 during the source's low-flux state. Circinus X-1 is
an accreting neutron star that exhibits ultra-relativistic arcsecond-scale
radio jets and diffuse arcminute-scale radio jets and lobes. The image shows a
clear excess along the general direction of the north-western counter-jet,
coincident with the radio emission, suggesting that it originates either in the
jet itself or in the shock the jet is driving into its environment. This makes
Circinus X-1 the first neutron star for which an extended X-ray jet has been
detected. The kinetic jet power we infer is significantly larger than the
minimum power required for the jet to inflate the large scale radio nebula.Comment: Added journal reference, corrected on reference and typo in labels
for Fig. 1; 5 pages, 3 figures, ApJ Letter, in pres
Premise Selection and External Provers for HOL4
Learning-assisted automated reasoning has recently gained popularity among
the users of Isabelle/HOL, HOL Light, and Mizar. In this paper, we present an
add-on to the HOL4 proof assistant and an adaptation of the HOLyHammer system
that provides machine learning-based premise selection and automated reasoning
also for HOL4. We efficiently record the HOL4 dependencies and extract features
from the theorem statements, which form a basis for premise selection.
HOLyHammer transforms the HOL4 statements in the various TPTP-ATP proof
formats, which are then processed by the ATPs. We discuss the different
evaluation settings: ATPs, accessible lemmas, and premise numbers. We measure
the performance of HOLyHammer on the HOL4 standard library. The results are
combined accordingly and compared with the HOL Light experiments, showing a
comparably high quality of predictions. The system directly benefits HOL4 users
by automatically finding proofs dependencies that can be reconstructed by
Metis
Role of Umklapp Processes in Conductivity of Doped Two-Leg Ladders
Recent conductivity measurements performed on the hole-doped two-leg ladder
material reveal an approximately linear
power law regime in the c-axis DC resistivity as a function of temperature for
. In this work, we employ a bosonic model to argue that umklapp processes
are responsible for this feature and for the high spectral weight in the
optical conductivity which occurs beyond the finite frequency Drude-like peak.
Including quenched disorder in our model allows us to reproduce experimental
conductivity and resistivity curves over a wide range of energies. We also
point out the differences between the effect of umklapp processes in a single
chain and in the two-leg ladder.Comment: 10 pages, 2 figure
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