bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of electron collisions on ion-acoustic waves and heat flow
Authors: Epperlein E. M.
Published: July 2002

The damping rate of ion-acoustic waves in a plasma is calculated by numerically solving the electron Fokker–Planck and cold-ion fluid equations for arbitrary electron collisionality kλei and charge number Z. The damping rate reaches a maximum at kλei∼(Zme/mi)1/2, as predicted by fluid theory, but then remains above fluid-theory predictions for kλei≳(Zme/mi)1/2. This enhancement is most significant for high-Z plasmas, where the thermalization due to electron–electron (e–e) collisions is least effective. For kλei≫1, the damping approaches the collisionless Landau limit. The isotropic-Rosenbluth-potential approximation for e–e collisions gives rise to errors of up to 10% in the damping rates. A further approximation that involves adjusting the e–i angular scattering collision strength to simulate the contribution from e–e collisions is found to be similarly accurate. In the high-Z limit, there is a strong reduction in the effective thermal conductivity κ relative to the classical Spitzer–Härm value κSH for kλei≳10−4. For low-Z plasmas, this reduction only becomes significant for kλei≳10−2. By introducing a spatially modulated inverse-bremsstrahlung heating source and solving for the steady-state distribution function, a further reduction in the value of κ/κSH is obtained.
Multisplitting and collapse of self-focusing anisotropic beams in normal/anomalous dispersive media
Authors: Bergé Luc , Rasmussen Jens Juul
Published: July 2002

Three-dimensional self-focusing light pulses in normal and anomalous dispersive media are investigated by means of a waveguide instability analysis, a Lagrangian approach, and a quasi-self-similar analysis. In the case of normal dispersion for which no localized ground state exists, it is shown that a high-intensity elongated beam cannot self-similarly collapse. Even when the incident beam power widely exceeds the critical power for a two-dimensional self-focusing, the beam is shown to split into multiple cells that ultimately disperse when their individual mass lies below the critical power. The mechanism underlying this fragmentation process is described in terms of a stretching of the self-focusing beam along its propagation axis. The focal point, where the splitting process develops, is identified. Finally, it is shown that the longitudinal dynamical motions of self-focusing elongated pulses also play an important role in an anomalous dispersive medium. In this case, unlike the former one, the beam self-contracts along its propagation axis and reconcentrates its shape back toward the center where it ultimately collapses in a finite time.
Dust-acoustic solitary waves and double layers in dusty plasma consisting of cold dust particles and two-temperature isothermal ions
Authors: Tagare S. G.
Published: July 2002

It is found that a dusty plasma with inertial dust fluid and two-temperature isothermal ions admits both compressive and rarefactive solitary waves, as well as compressive and rarefactive double layers (depending on the concentration of low-temperature ions). In this paper, Korteweg-de Vries equation (KdV-type equations) with cubic and fourth-order nonlinearity at the critical density of low-temperature isothermal ions are derived to discuss properties of dust-acoustic solitary waves. In the vicinity of critical density of low-temperature ions, KdV-type equation with mixed nonlinearity is discussed. By using quasipotential analysis, critical Mach numbers M1c and M2c are obtained such that rarefactive dust-acoustic solitons exist when 1<M<M1c and compressive dust acoustic solitons exist when 1<M<M2c.
Electron surface waves in a nonuniform plasma slab
Authors: Cooperberg D. J.
Published: July 2002

Electron surface waves in a nonuniform, metal bound, thermal plasma slab have been analyzed and detected. Measurements of the dispersion relations of these waves, as well as the eigenstructure of the perturbed electron density, reveal a spectrum of waves with frequencies above and below the peak electron plasma frequency in the slab. These waves are analogous to the Gould–Trivelpiece and Tonks–Dattner waves found in dielectric bound plasma columns. Measurements have been made using particle-in-cell simulation of an argon plasma and are compared with linear fluid theory in which the adiabatic approximation is made for the perturbed pressure. The presence of the metal boundary leads to regions near the plasma sheaths in which the fluid theory breaks down; we explore the differences between theory and measurement in this region.
Korteweg-de Vries equation of ion acoustic surface waves
Authors: Hong Hee Sook , Lee Hee J.
Published: July 2002

A Korteweg-de Vries (KdV) equation is derived for an ion acoustic surface wave propagating on the interface between a plasma and vacuum, using two-fluid equations. The nonlinearity responsible for the KdV equation is found to be the nonlinear current at the boundary.
Onset of high-n ballooning modes during tokamak sawtooth crashes
Authors: Nishimura Y. , Callen J. D. , Hegna C. C.
Published: July 2002

A new phenomenon has been found during the nonlinear stage of the tokamak sawtooth crash in relatively high β plasmas. The m/n=1/1 magnetic island evolution gives rise to convection of the pressure inside the q=1 radius and builds up steep pressure gradient across the island separatrix, and thereby trigger ballooning instabilities below the threshold at the equilibrium. Effects of the ballooning modes on the magnetic reconnection process during the sawtooth crash are discussed.
Ion-acoustic solitons and double layers in a two-electron temperature plasma with hot isothermal electrons and cold ions
Authors: Tagare S. G.
Published: July 2002

It is found that a two-electron temperature plasma with isothermal electrons and cold ions admits both compressive and rarefactive solitons, as well as compressive and rarefactive double layers (depending on the concentration of low-temperature electrons). In this paper, a Korteweg–de Vries (K-dV) equation and a K-dV-type equation with cubic and fourth-order nonlinearity at the critical density of the low-temperature isothermal electrons are derived to discuss the properties of ion-acoustic solitons in a two-electron temperature plasma. In the vicinity of the critical electron density of low-temperature isothermal electrons, we have derived a K-dV-type equation with mixed nonlinearity, and the solution of this equation will have both compressive and rarefactive double layers for those values of critical electron density of low-temperature electrons for which ion-acoustic solitons do not exist. By using quasipotential analysis, critical Mach numbers M1c and M2c are obtained such that compressive ion-acoustic solitons exist when 1<M<M1c and rarefactive ion-acoustic solitons exist when 1<M<M2c.
Effects of radiation on direct-drive laser fusion targets
Authors: Colombant D. G. , Bodner S. E. , Schmitt A. J. , Klapisch M. , Gardner J. H. , Aglitskiy Y. , Deniz A. V. , Obenschain S. P. , Pawley C. J. , Serlin V. , Weaver J. L.
Published: July 2002

The role played by radiation in the radiation-preheated direct-drive laser fusion target design is discussed. The soft x-rays emitted during the foot of the laser pulse—at a few 1012 W/cm2—preheat the low-opacity foam ablator which helps to control the Rayleigh–Taylor instability. The foam opacity is, however, thick enough to stop that radiation, keeping the fuel on a low adiabat. Radiation effects are also important in the blow-off corona of the target because they establish a long scale-length plasma. This may help to shield the ablation region from the nonuniformities in the laser absorption.
Drawing-induced 1.53-μm wavelength optical loss in single-mode fibers drawn at high speeds
Authors: Sakaguchi S. , Itoh H. , Hanawa F. , Kimura T.
Published: July 2002

Optical loss at 1.53-μm wavelength is observed in silica-based single-mode fibers drawn at high speeds. This loss, which is induced by high-speed drawing, is attributed to silylidyne group absorption. It is found that silica glass fibers occasionally contain hydrogens associated with silicons in addition to hydroxyl groups.
Finite element analysis of the diamond anvil cell: Achieving 4.6 Mbar
Authors: Moss William C. , Hallquist John O. , Reichlin Robin , Goettel Kenneth A. , Martin Sue
Published: July 2002

We have performed a comprehensive finite element analysis of the diamond anvil cell. Our analysis shows how beveled diamonds and material properties of the gasket affect diamond anvil cell performance. Using the results of the analysis, we have achieved 4.6 Mbar experimentally, which is the highest static pressure reported to date. Possible methods to increase the pressure further are discussed.
Operation of the Si/CoSi2/Si heterostructure transistor
Authors: Hensel J. C.
Published: July 2002

A two-current path model is presented to describe the operation of the Si/CoSi2/Si epitaxial, heterostructure transistor. The model gives a good account of the device behavior and allows us to conclude that it works by activated charge control, in a formal sense like a bipolar transistor. The analysis further suggests that with the fine base dimensions made possible by the single crystal, vertical structure one can foresee devices with β’s of a 100 or more, at the same time maintaining a transconductance close to the optimal value 0.04 mhos/mA characteristic of a charge injection device.
Nearly ideal electronic properties of sulfide coated GaAs surfaces
Authors: Yablonovitch E. , Sandroff C. J. , Bhat R. , Gmitter T.
Published: July 2002

We have discovered that a class of inorganic sulfides [Li2S, (NH4)2S, Na2S⋅9H2O, etc.] imparts excellent electronic properties to GaAs surfaces. The surface recombination velocity at the interface between Na2S⋅9H2O and GaAs begins to approach that of the nearly ideal AlGaAs/GaAs interface. We propose the formation of a robust covalently bonded sulfide layer to explain the favorable electronic quality of such interfaces.
Determination of the electron diffusion length in p-GaP by intensity modulated photocurrent measurements with an electrolyte contact
Authors: Peat R. , Peter L. M.
Published: July 2002

Sinusoidal intensity modulation in the frequency range 1 Hz–65 kHz has been used to study the frequency dependence of the photocurrent at the p-GaP/0.5 M H2SO4 junction. It is shown that the high-frequency response is independent of surface recombination, so that the diffusion length of electrons and the absorption coefficient of the semiconductor can be derived. In the case of p-GaP, the electron diffusion length was found to be (7.9±0.8)×10−6 cm, and the absorption coefficient at 442 nm was calculated to be (3.2±0.3)×104 cm−1.
Picosecond photoelectron scanning electron microscope for noncontact testing of integrated circuits
Authors: May P. , Halbout J.-M. , Chiu G.
Published: July 2002

A scanning electron microscope which uses an ultrashort pulsed laser/photocathode combination as an electron source produces electron pulses of order 1 ps in duration at a 100-MHz repetition rate and with a peak brightness of 3×108 A/cm2 steradian at 1.8 keV. By using this instrument in the voltage contrast mode, without contact with the samples, we have been able to measure electrical pulses propagating on coplanar transmission lines with, simultaneously, a temporal resolution of 5 ps, a voltage resolution of 3 mV/(Hz)1/2, and a spatial resolution of 0.1 μm. These measurements are achieved with extraction fields above the sample of about 1 kV/mm.
Consequences of placing an intramolecular crosslink in myosin S1
Authors: Konno Kunihiko , Ue Kathleen , Khoroshev Mikhail , Martinez Hugo , Ray Bruce , Morales Manuel F.
Published: July 2002

This paper describes the placement of a crosslinking agent (dibromobimane) between two thiols (Cys-522 and Cys-707) of a fragment, “S1,” of the motor protein, myosin. It turns out that fastening the first anchor of the crosslinker is easy and rapid, but fastening the second anchor (Cys-522) is very temperature dependent, taking 30 min at room temperature but about a week on ice. Moreover, crystallography taken at 4°C would seem to predict that the linkage is impossible, because the span of the crosslinking agent is much less than the interthiol distance. The simplest resolution of this seeming paradox is that structural fluctuations of the protein render the linkage increasingly likely as the temperature increases. Also, measurements of the affinity of MgADP for the protein, as well as the magnetic resonance of the P-atoms of the ADP once emplaced, suggest that binding the first reagent anchor to Cys-707 initiates an influence that travels to the rather distant ADP-binding site, and it is speculated what this “path of influence” might be.
Dendritic cells purified from myeloma are primed with tumor-specific antigen (idiotype) and activate CD4+T cells
Authors: Dembic Zlatko , Schenck Karl , Bogen Bjarne
Published: July 2002

Multiple myelomas produce tumor-specific antigen (TSA) in the form of idiotype (Id) on monoclonal Ig. CD4+T cells can recognize Id-peptide on MHC class II molecules and protect against challenges with MOPC315 cells, which are, as common for myelomas, class II-negative. The present study explains these previous results by demonstrating that Id can be transferred from myeloma cells to antigen-presenting cells (APC), which present processed Id-peptide on their class II molecules to Id-specific T cell receptor-transgenic (TCR-TG) CD4+T cells. Id-primed tumor APC were heterogeneous, the majority being dendritic cells with class II+, CD11b+CD11c+CD40+CD80+CD86+markers. The APC were localized beneath CD31+endothelial cells of tumor microvessels, and their frequency declined with tumor progression. The APC could stimulate Id-specific naive TCR-TG, short-term polarized TCR-TG, and cloned CD4+T cells to proliferate and produce cytokinesin vitro. Furthermore, small MOPC315 tumors established in Id-specific TCR-TG mice contained clusters of activated (CD69+CD25+) and proliferating (BrdUrd+) Id-specific transgenic CD4+blasts. The activated Id-specific T cells were located adjacent to Id-primed dendritic cells in the tumor. Thus, a TSA can be transferredin vivofrom myeloma, and possibly other types of cancer cells to APC for MHC class II presentation to CD4+T cells.
Interactions among the protein and RNA subunits ofSaccharomyces cerevisiaenuclear RNase P
Authors: Houser-Scott Felicia , Xiao Shaohua , Millikin Christopher E. , Zengel Janice M. , Lindahl Lasse , Engelke David R.
Published: July 2002

Ribonuclease P (RNase P) is a ubiquitous endoribonuclease that cleaves precursor tRNAs to generate mature 5′ termini. Although RNase P from all kingdoms of life have been found to have essential RNA subunits, the number and size of the protein subunits ranges from one small protein in bacteria to at least nine proteins of up to 100 kDa. InSaccharomyces cerevisiaenuclear RNase P, the enzyme is composed of ten subunits: a single RNA and nine essential proteins. The spatial organization of these components within the enzyme is not yet understood. In this study we examine the likely binary protein–protein and protein–RNA subunit interactions by using directed two- and three-hybrid tests in yeast. Only two protein subunits, Pop1p and Pop4p, specifically bind the RNA subunit. Pop4p also interacted with seven of the other eight protein subunits. The remaining protein subunits all showed one or more specific protein–protein interactions with the other integral protein subunits. Of particular interest was the behavior of Rpr2p, the only protein subunit found in RNase P but not in the closely related enzyme, RNase MRP. Rpr2p interacts strongly with itself as well as with Pop4p. Similar interactions with self and Pop4p were also detected for Snm1p, the only unique protein subunit so far identified in RNase MRP. This observation is consistent with Snm1p and Rpr2p serving analogous functions in the two enzymes. This study provides a low-resolution map of the multisubunit architecture of the ribonucleoprotein enzyme, nuclear RNase P fromS. cerevisiae.
CD95/Fas induces cleavage of the GrpL/Gads adaptor and desensitization of antigen receptor signaling
Authors: Yankee Thomas M. , Draves Kevin E. , Ewings Maria K. , Clark Edward A. , Graves Jonathan D.
Published: July 2002

The balance between cell survival and cell death is critical for normal lymphoid development. This balance is maintained by signals through lymphocyte antigen receptors and death receptors such as CD95/Fas. In some cells, ligating the B cell antigen receptor can protect the cell from apoptosis induced by CD95. Here we report that ligation of CD95 inhibits antigen receptor-mediated signaling. Pretreating CD40-stimulated tonsillar B cells with anti-CD95 abolished B cell antigen receptor-mediated calcium mobilization. Furthermore, CD95 ligation led to the caspase-dependent inhibition of antigen receptor-induced calcium mobilization and to the activation of mitogen-activated protein kinase pathways in B and T cell lines. A target of CD95-mediated caspase 3-like activity early in the apoptotic process is the adaptor protein GrpL/Gads. GrpL constitutively interacts with SLP-76 via its C-terminal SH3 domain to regulate transcription factors such as NF-AT. Cleavage of GrpL removes the C-terminal SH3 domain so that it is no longer capable of recruiting SLP-76 to the membrane. Transfection of a truncated form of GrpL into Jurkat T cells blocked T cell antigen receptor-induced activation of NF-AT. These results suggest that CD95 signaling can desensitize antigen receptors, in part via cleavage of the GrpL adaptor.
Clonable progenitors committed to the T lymphocyte lineage in the mouse bone marrow; use of an extrathymic pathway
Authors: Dejbakhsh-Jones Sussan , García-Ojeda Marcos E. , Chatterjea-Matthes Devavani , Zeng Defu , Strober Samuel
Published: July 2002

We searched for clonable committed T cell progenitors in the adult mouse bone marrow and isolated rare (≈0.05%) cells with the Thy-1hiCD2−CD16+CD44hiCD25−Lin−phenotype.In vivoexperiments showed that these cells were progenitors committed only to reconstituting the T cell lineage of irradiated Ly5 congenic hosts. Reconstitution of the thymus was minimal compared with that of the bone marrow, spleen, and lymph nodes. At limiting dilutions, donor T cell reconstitution of the spleen frequently occurred without detectable donor cells in the thymus. Progenitors were capable of rapidly reconstituting athymic hosts. In conclusion, the clonable bone marrow progenitors were capable of T cell reconstitution predominantly by means of an extrathymic pathway.
Spectroscopic studies of the vibrational and electronic properties of solid hydrogen to 285 GPa
Authors: Goncharov Alexander F. , Gregoryanz Eugene , Hemley Russell J. , Mao Ho-kwang
Published: July 2002

We report Raman scattering and visible to near-infrared absorption
spectra of solid hydrogen under static pressure up to 285 GPa between
20 and 140 K. We obtain pressure dependences of vibron and
phonon modes consistent with results previously determined to lower
pressures. The results indicate the stability of the ordered molecular
phase III to the highest pressure reached and provide constraints on
the insulator-to-metal transition pressure.
Switch junction sequences in PMS2-deficient mice reveal a microhomology-mediated mechanism of Ig class switch recombination
Authors: Ehrenstein Michael R. , Rada Cristina , Jones Anne-Marie , Milstein César , Neuberger Michael S.
Published: July 2002

Isotype switching involves a region-specific, nonhomologous
recombinational deletion that has been suggested to occur by
nonhomologous joining of broken DNA ends. Here, we find
increased donor/acceptor homology at switch junctions from
PMS2-deficient mice and propose that class switching can occur by
microhomology-mediated end-joining. Interestingly, although isotype
switching and somatic hypermutation show many parallels, we confirm
that PMS2 deficiency has no major effect on the pattern of nucleotide
substitutions generated during somatic hypermutation. This finding is
in contrast to MSH2 deficiency. With MSH2, the altered pattern of
switch recombination and hypermutation suggests parallels in the
mechanics of the two processes, whereas the fact that PMS2 deficiency
affects only switch recombination may reflect differences in the
pathways of break resolution.
Substrate-bound agrin induces expression of acetylcholine receptor epsilon-subunit gene in cultured mammalian muscle cells.
Authors: Jones G , Herczeg A , Ruegg M A , Lichtsteiner M , Kröger S , Brenner H R
Published: July 2002

Expression of the epsilon-subunit gene of the acetylcholine receptor (AChR) by myonuclei located at the neuromuscular junction is precisely regulated during development. A key role in this regulation is played by the synaptic portion of the basal lamina, a structure that is also known to contain agrin, a component responsible for the formation of postsynaptic specializations. We tested whether agrin has a function in synaptic AChR gene expression. Synaptic basal lamina from native adult muscle and recombinant agrin bound to various substrates induced in cultured rat myotubes AChR clusters that were colocalized with epsilon-subunit mRNA. Estimation of transcript levels by Northern hybridization analysis of total RNA showed a significant increase when myotubes were grown on substrate impregnated with agrin, but were unchanged when agrin was applied in the medium. The effect was independent of the receptor aggregating activity of the agrin isoform used, and agrin acted, at least in part, at the level of epsilon-subunit gene transcription. These findings are consistent with a role of agrin in the regulation of AChR subunit gene expression at the neuromuscular junction, which would depend on its binding to the synaptic basal lamina.
Expression of a candidate cadherin in T lymphocytes.
Authors: Cepek K L , Rimm D L , Brenner M B
Published: July 2002

Cadherins are homotypic adhesion molecules that classically mediate interactions between cells of the same type in solid tissues. In addition, E-cadherin is able to support homotypic adhesion of epidermal Langerhans cells to keratinocytes (Tang, A., Amagai, M., Granger, L. G., Stanley, J. R. & Udey, M. C. (1993) Nature (London) 361, 82-85) and heterotypic adhesion of mucosal epithelial cells to E-cadherin-negative intestinal intraepithelial T lymphocytes. Thus, we hypothesized that cadherins may play a wider role in cell-to-cell adhesion events involving T lymphocytes. We searched for a cadherin or cadherins in T lymphocytes with a pan-cadherin antiserum and antisera against alpha- or beta-catenin, molecules known to associate with the cytoplasmic domain of cadherins. The anti-beta-catenin antisera coimmunoprecipitated a radiolabeled species in T-lymphocyte lines that had a molecular mass of 129 kDa and was specifically immunoblotted with the pan-cadherin antiserum. Also, the pan-cadherin antiserum directly immunoprecipitated a 129-kDa radiolabeled species from an 125I surface-labeled Jurkat human T-cell leukemic cell line. After V8 protease digestion, the peptide map of this pan-cadherin-immunoprecipitated, 129-kDa species exactly matched that of the 129-kDa species coimmunoprecipitated with the beta-catenin antiserum. These results demonstrate that T lymphocytes express a catenin-associated protein that appears to be a member of the cadherin superfamily and may contribute to T cell-mediated immune surveillance.
A high-resolution annotated physical map of the human chromosome 13q12-13 region containing the breast cancer susceptibility locus BRCA2.
Authors: Fischer S G , Cayanis E , de Fatima Bonaldo M , Bowcock A M , Deaven L L , Edelman I S , Gallardo T , Kalachikov S , Lawton L , Longmire J L , Lovett M , Osborne-Lawrence S , Rothstein R , Russo J J , Soares M B , Sunjevaric I , Venkatraj V S , Warburton D , Zhang P , Efstratiadis A
Published: July 2002

Various types of physical mapping data were assembled by developing a set of computer programs (Integrated Mapping Package) to derive a detailed, annotated map of a 4-Mb region of human chromosome 13 that includes the BRCA2 locus. The final assembly consists of a yeast artificial chromosome (YAC) contig with 42 members spanning the 13q12-13 region and aligned contigs of 399 cosmids established by cross-hybridization between the cosmids, which were selected from a chromosome 13-specific cosmid library using inter-Alu PCR probes from the YACs. The end sequences of 60 cosmids spaced nearly evenly across the map were used to generate sequence-tagged sites (STSs), which were mapped to the YACs by PCR. A contig framework was generated by STS content mapping, and the map was assembled on this scaffold. Additional annotation was provided by 72 expressed sequences and 10 genetic markers that were positioned on the map by hybridization to cosmids.
Molecular markers reveal that population structure of the human pathogen Candida albicans exhibits both clonality and recombination.
Authors: Gräser Y , Volovsek M , Arrington J , Schönian G , Presber W , Mitchell T G , Vilgalys R
Published: July 2002

The life history of Candida albicans presents an enigma: this species is thought to be exclusively asexual, yet strains show extensive phenotypic variation. To address the population genetics of C. albicans, we developed a genetic typing method for codominant single-locus markers by screening randomly amplified DNA for single-strand conformation polymorphisms. DNA fragments amplified by arbitrary primers were initially screened for single-strand conformation polymorphisms and later sequenced using locus-specific primers. A total of 12 single base mutations and insertions were detected from six out of eight PCR fragments. Patterns of sequence-level polymorphism observed for individual strains detected considerable heterozygosity at the DNA sequence level, supporting the view that most C. albicans strains are diploid. Population genetic analyses of 52 natural isolates from Duke University Medical Center provide evidence for both clonality and recombination in C. albicans. Evidence for clonality is supported by the presence of several overrepresented genotypes, as well as by deviation of genotypic frequencies from random (Hardy-Weinberg) expectations. However, tests for nonrandom association of alleles across loci reveal less evidence for linkage disequilibrium than expected for strictly clonal populations. Although C. albicans populations are primarily clonal, evidence for recombination suggests that sexual reproduction or some other form of genetic exchange occurs in this species.
Functional domains for assembly of histones H3 and H4 into the chromatin of
Xenopus
embryos
Authors: Freeman Lita , Kurumizaka Hitoshi , Wolffe Alan P.
Published: July 2002

Histones H3 and H4 have a well defined structural role in the
nucleosome and an established role in the regulation of transcription.
We have made use of a microinjection strategy using
Xenopus
embryos to define the minimal structural
components of H3 and H4 necessary for nucleosome assembly into metazoan
chromosomes
in vivo
. We find that both the N-terminal
tail of H4, including all sites of acetylation, and the C-terminal
α-helix of the H4 histone fold domain are dispensable for chromatin
assembly. The N-terminal tail and an N-terminal α-helix of H3 are
also dispensable for chromatin assembly. However, the remainder of the
H3 and H4 histone folds are essential for incorporation of these
proteins into chromatin. We suggest that elements of the histone fold
domain maintain both nucleosomal integrity and have distinct functions
essential for cell viability.
A
Drosophila
homolog of the tumor suppressor gene adenomatous polyposis coli down-regulates β-catenin but its zygotic expression is not essential for the regulation of Armadillo
Authors: Hayashi Shigemi , Rubinfeld Bonnee , Souza Brian , Polakis Paul , Wieschaus Eric , Levine Arnold J.
Published: July 2002

Mutations in the adenomatous polyposis coli gene (which encodes a
protein called APC) are associated with the formation of intestinal
polyps and colon cancers. To facilitate the functional study of APC we
have isolated its
Drosophila
homolog (D-APC) by
screening an expression library with an antibody against human APC. The
isolated cDNA encodes a predicted 2416-amino acid protein containing
significant homology to multiple domains of mammalian APCs. D-APC has
seven complete armadillo repeats with 60% identity to its human
homolog, one β-catenin binding site, and up to 7 copies of a 20-amino
acid repeat with the average of 50% identity to human APC at amino
acid level. D-APC, like its human counterpart, also contains a basic
domain. Expression of the domain of D-APC homologous to the region
required for β-catenin down-regulation resulted in down-regulation of
intracellular β-catenin in a mammalian cell line. This same region
bound to the Armadillo (Arm) protein,
in vitro
, the
Drosophila
homolog of β-catenin. D-APC RNA and protein
expression is very low, if detectable at all, during stages when Arm
protein accumulates in a striped pattern in the epidermis of the
Drosophila
embryos. Removing zygotic D-APC expression
did not alter Arm protein distribution, and the final cuticle pattern
was not affected significantly. As observed in the rodent, high levels
of D-APC expression have been detected in the central nervous system,
suggesting a role for D-APC in central nervous system formation.
Calpain is a mediator of preservation-reperfusion injury in rat liver transplantation
Authors: Kohli Vivek , Gao Wenshi , Camargo Carlos A. , Clavien Pierre Alain
Published: July 2002

Proteases as well as alterations in intracellular calcium have important roles in hepatic preservation-reperfusion injury, and increased calpain activity recently has been demonstrated in liver allografts. Experiments were designed to evaluate (i) hepatic cytosolic calpain activity during different periods of cold ischemia (CI), rewarming, or reperfusion, and (ii) effects of inhibition of calpain on liver graft function using the isolated perfused rat liver and arterialized orthotopic liver transplantation models. Calpain activity was assayed using the fluorogenic substrate Suc-Leu-Leu-Val-Tyr-7-amino-4-methyl coumarin (AMC) and expressed as mean ± SD pmol AMC released/min per mg of cytosolic protein. Calpain activity rose significantly after 24 hr of CI in University of Wisconsin solution and further increased with longer preservation. Activity also increased within 30 min of rewarming, peaking at 120 min. Increased durations of CI preceding rewarming resulted in significantly higher activity (P< 0.01). Calpain activity increased rapidly upon reperfusion and was significantly enhanced by previous CI (P< 0.01). Calpain inhibition with Cbz-Val-Phe methyl ester significantly decreased aspartate aminotransferase released in the isolated perfused rat liver perfusate (P< 0.05). Duration of survival after orthotopic liver transplantation using livers cold-preserved for 40 hr was also significantly increased (P< 0.05) with calpain inhibitor. In conclusion, calpain proteases are activated during each phase of transplantation and are likely to play an important role in the mechanisms of preservation-reperfusion injury.
A critical role of Lyn and Fyn for B cell responses to CD38 ligation and interleukin 5
Authors: Yasue Tokutaro , Nishizumi Hirofumi , Aizawa Shinichi , Yamamoto Tadashi , Miyake Kensuke , Mizoguchi Chieko , Uehara Shoji , Kikuchi Yuji , Takatsu Kiyoshi
Published: July 2002

CD38 ligation on mouse B cells by CS/2, an anti-mouse CD38 mAb, induced proliferation, interleukin 5 (IL-5) receptor α chain expression, and tyrosine phosphorylation of Bruton tyrosine kinase (Btk) from wild-type, but not from X chromosome-linked, immunodeficient mice. B cells fromfyn-deficient (Fyn−/−) andlyn-deficient (Lyn−/−) mice showed an impaired response to mAb CS/2 for proliferation and IL-5 receptor α chain expression, and B cells fromfyn/lyndouble-deficient (Fyn/Lyn−/−) mice did not respond at all to mAb CS/2. The Btk activation by CD38 ligation was observed in B cells from Fyn−/−mice, and it was severely impaired in B cells from Lyn−/−and Fyn/Lyn−/−mice. CD38 expression on B cells from three mutant strains was comparable to that on control B cells. We infer from these results that both Fyn and Lyn are required and that their signals are synergistic for B cell triggering after CD38 ligation. Lyn is upstream of Btk activation in the CD38 signaling. Stimulation of B cells with IL-5 together with CD38 ligation induces not only IgM but also IgG1 secretion. Analysis of the synergistic effects of IL-5 and CD38 ligation on IgG1 secretion revealed the impaired IgG1 secretion of B cells from Lyn−/−and Fyn/Lyn−/−mice. These data imply that Lyn is involved in B cell triggering by CD38 ligation plus IL-5 for isotype switching.
Block of transmitter release by botulinum C1 action on syntaxin at the squid giant synapse
Authors: Marsal Jordi , Ruiz-Montasell Bonaventura , Blasi Joan , Moreira Jorge E. , Contreras Diego , Sugimori Mutsuyuki , Llinás Rodolfo
Published: July 2002

Electrophysiological, morphological, and biochemical approaches were combined to study the effect of the presynaptic injection of the light chain of botulinum toxin C1 into the squid giant synapse. Presynaptic injection was accompanied by synaptic block that occurred progressively as the toxin filled the presynaptic terminal. Neither the presynaptic action potential nor the Ca
2+
currents in the presynaptic terminal were affected by the toxin. Biochemical analysis of syntaxin moiety in squid indicates that the light chain of botulinum toxin C1 lyses syntaxin
in vitro
, suggesting that this was the mechanism responsible for synaptic block. Ultrastructure of the injected synapses demonstrates an enormous increase in the number of presynaptic vesicles, suggesting that the release rather than the docking of vesicles is affected by biochemical lysing of the syntaxin molecule.
Inactivation of DNA proofreading obviates the need for SOS induction in frameshift mutagenesis
Authors: Fuchs Robert P. P. , Napolitano Rita L.
Published: July 2002

Translesion synthesis at replication-blocking lesions requires the induction of proteins that are controlled by the SOS system in
Escherichia coli
. Of the proteins identified so far, UmuD′, UmuC, and RecA* were shown to facilitate replication across UV-light-induced lesions, yielding both error-free and mutagenic translesion-synthesis products. Similar to UV lesions,
N
-2-acetylaminofluorene (AAF), a chemical carcinogen that forms covalent adducts at the C8 position of guanine residues, is a strong replication-blocking lesion. Frameshift mutations are induced efficiently by AAF adducts when located within short repetitive sequences in a two-step mechanism; AAF adducts incorporate a cytosine across from the lesion and then form a primer-template misaligned intermediate that, upon elongation, yields frameshift mutations. Recently, we have shown that although elongation from the nonslipped intermediate depends on functional
umuDC
+
gene products, elongation from the slipped intermediate is
umuDC
+
-independent but requires another, as yet biochemically uncharacterized, SOS function. We now show that in DNA Polymerase III-proofreading mutant strains (
dnaQ49
and
mutD5
strains), elongation from the slipped intermediate is highly efficient in the absence of SOS induction—in contrast to elongation from the nonslipped intermediate, which still requires UmuDC functions.
Proton uptake controls electron transfer in cytochrome
c
oxidase
Authors: Karpefors Martin , Ädelroth Pia , Zhen Yuejun , Ferguson-Miller Shelagh , Brzezinski Peter
Published: July 2002

In cytochrome
c
oxidase, a requirement for proton pumping is a tight coupling between electron and proton transfer, which could be accomplished if internal electron-transfer rates were controlled by uptake of protons. During reaction of the fully reduced enzyme with oxygen, concomitant with the “peroxy” to “oxoferryl” transition, internal transfer of the fourth electron from Cu
A
to heme
a
has the same rate as proton uptake from the bulk solution (8,000 s
−1
). The question was therefore raised whether the proton uptake controls electron transfer or vice versa. To resolve this question, we have studied a site-specific mutant of the
Rhodobacter sphaeroides
enzyme in which methionine 263 (SU II), a Cu
A
ligand, was replaced by leucine, which resulted in an increased redox potential of Cu
A
. During reaction of the reduced mutant enzyme with O
2
, a proton was taken up at the same rate as in the wild-type enzyme (8,000 s
−1
), whereas electron transfer from Cu
A
to heme
a
was impaired. Together with results from studies of the EQ(I-286) mutant enzyme, in which both proton uptake and electron transfer from Cu
A
to heme
a
were blocked, the results from this study show that the Cu
A
→ heme
a
electron transfer is controlled by the proton uptake and not vice versa. This mechanism prevents further electron transfer to heme
a
3
–Cu
B
before a proton is taken up, which assures a tight coupling of electron transfer to proton pumping.
Syntaxin 1 interacts with the L
D
subtype of voltage-gated Ca
2+
channels in pancreatic β cells
Authors: Yang Shao-Nian , Larsson Olof , Bränström Robert , Bertorello Alejandro M. , Leibiger Barbara , Leibiger Ingo B. , Moede Tilo , Köhler Martin , Meister Björn , Berggren Per-Olof
Published: July 2002

Interaction of syntaxin 1 with the α
1D
subunit of the voltage-gated L type Ca
2+
channel was investigated in the pancreatic β cell. Coexpression of the enhanced green fluorescent protein-linked α
1D
subunit with the enhanced blue fluorescent protein-linked syntaxin 1 and Western blot analysis together with subcellular fractionation demonstrated that the α
1D
subunit and syntaxin 1 were colocalized in the plasma membrane. Furthermore, the α
1D
subunit was coimmunoprecipitated efficiently by a polyclonal antibody against syntaxin 1. Syntaxin 1 also played a central role in the modulation of L type Ca
2+
channel activity because there was a faster Ca
2+
current run-down in cells incubated with antisyntaxin 1 compared with controls. In parallel, antisyntaxin 1 markedly reduced insulin release in both intact and permeabilized cells, subsequent to depolarization with K
+
or exposure to high Ca
2+
. Exchanging Ca
2+
for Ba
2+
abolished the effect of antisyntaxin 1 on both Ca
2+
channel activity and insulin exocytosis. Moreover, antisyntaxin 1 had no significant effects on Ca
2+
-independent insulin release trigged by hypertonic stimulation. This suggests that there is a structure–function relationship between the α
1D
subunit of the L type Ca
2+
channel and the exocytotic machinery in the pancreatic β cell.
Purification of ribonucleotide reductase subunits Y1, Y2, Y3, and Y4 from yeast: Y4 plays a key role in diiron cluster assembly
Authors: Nguyen Hiep-Hoa T. , Ge Jie , Perlstein Deborah L. , Stubbe JoAnne
Published: July 2002

Ribonucleotide reductases (RNRs) catalyze the conversion of nucleotides to deoxynucleotides. Class I RNRs are composed of two types of subunits: RNR1 contains the active site for reduction and the binding sites for the nucleotide allosteric effectors. RNR2 contains the diiron-tyrosyl radical (Y⋅) cofactor essential for the reduction process. Studies in yeast have recently identified four RNR subunits: Y1 and Y3, Y2 and Y4. These proteins have been expressed in
Saccharomyces cerevisiae
and in
Escherichia coli
and purified to ≈90% homogeneity. The specific activity of Y1 isolated from yeast and
E. coli
is 0.03 μmol⋅min
−1
⋅mg
−1
and of (His)
6
-Y2 [(His)
6
-Y2-K387N] from yeast is 0.037 μmol⋅min
−1
⋅mg
−1
(0.125 μmol⋅min
−1
⋅mg
−1
). Y2, Y3, and Y4 isolated from
E. coli
have no measurable activity. Efforts to generate Y⋅ in Y2 or Y4 using Fe
2+
, O
2
, and reductant have been unsuccessful. However, preliminary studies show that incubation of Y4 and Fe
2+
with inactive
E. coli
Y2 followed by addition of O
2
generates Y2 with a specific activity of 0.069 μmol⋅min
−1
⋅mg
−1
and a Y⋅. A similar experiment with (His)
6
-Y2-K387N, Y4, O
2
, and Fe
2+
results in an increase in its specific activity to 0.30 μmol⋅min
−1
⋅mg
−1
. Studies with antibodies to Y4 and Y2 reveal that they can form a complex
in vivo
. Y4 appears to play an important role in diiron-Y⋅ assembly of Y2.
The polo-box-dependent induction of ectopic septal structures by a mammalian polo kinase, Plk, in
Saccharomyces cerevisiae
Authors: Lee Kyung S. , Song Sukgil , Erikson Raymond L.
Published: July 2002

Members of the polo subfamily of protein kinases play pivotal roles in cell-cycle control and proliferation. In addition to a high degree of sequence similarity in the kinase domain, polo kinases contain a strikingly conserved motif termed “polo-box” in the noncatalytic C-terminal domain. We have previously shown that the mammalian polo-like kinase Plk is a functional homolog of
Saccharomyces cerevisiae
Cdc5. Here, we show that, in a polo-box- and kinase activity-dependent manner, ectopic expression of Plk in budding yeast can induce a class of cells with abnormally elongated buds. In addition to localization at spindle poles and cytokinetic neck filaments, Plk induces and localizes to ectopic septin ring structures within the elongated buds. In contrast, mutations in the polo-box abolish both localization to, and induction of, septal structures. Consistent with the polo-box-dependent subcellular localization, the C-terminal domain of Plk, but not its polo-box mutant, is sufficient for subcellular localization. Our data suggest that Plk may contribute a signal to initiate or promote cytokinetic event(s) and that an intact polo-box is required for regulation of these cellular processes.
Identification of an early T cell progenitor for a pathway of T cell maturation in the bone marrow
Authors: Dejbakhsh-Jones Sussan , Strober Samuel
Published: July 2002

We have identified a rare (≈0.05–0.1%) population of cells (Thy-1hiCD16+CD44hiCD2−TCRαβ−B220−Mac-1−NK1.1−) in the adult mouse bone marrow that generates CD4+and CD8+TCRαβ+T cells after tissue culture for 48 hr in the presence of Ly5 congenic marrow cells. The essential stages in the maturation of the progenitors were determined; the stages included an early transition from CD2−CD16+CD44hiTCRαβ−to CD2+CD16int/−CD44int/−TCRαβ−cells, and a later transition to CD4+CD8+TCRαβ+double-positive T cells that rapidly generate the CD4+and CD8+single-positive T cells. The maturation of the progenitors is almost completely arrested at the CD2+TCRαβ−stage by the presence of mature T cells at the initiation of cultures. This alternate pathway is supported by the marrow microenvironment; it recapitulates critical intermediary steps in intrathymic T cell maturation.
Multivalent structure of an αβT cell receptor
Authors: Fernández-Miguel Gemma , Alarcón Balbino , Iglesias Antonio , Bluethmann Horst , Alvarez-Mon Melchor , Sanz Eva , de la Hera Antonio
Published: July 2002

Whether there is one or multiple αβT cell antigen receptor (TCR) recognition modules in a given TCR/CD3 complex is a long-standing controversy in immunology. We show that T cells from transgenic mice that coexpress comparable amounts of two distinct TCRβ chains incorporate at least two αβTCRs in a single TCR/CD3 complex. Evidence for bispecific αβTCRs was obtained by immunoprecipitation and immunoblotting and confirmed on the surface of living cells both by fluorescence resonance energy transfer and comodulation assays by using antibodies specific for TCRβ-variable regions. Such (αβ)2TCR/CD3 or higher-order complexes were evident in T cells studied eitherex vivoor after expansionin vitro. T cell activation is thought by many, but not all, to require TCR cross-linking by its antigen/major histocompatibility complex ligand. The implications of a multivalent (αβ)2TCR/CD3 complex stoichiometry for the ordered docking of specific antigen/major histocompatibility complex, CD4, or CD8 coreceptors and additional TCRs are discussed.
Novel mechanisms control the folding and assembly of λ5/14.1 and VpreB to produce an intact surrogate light chain
Authors: Minegishi Yoshiyuki , Hendershot Linda M. , Conley Mary Ellen
Published: July 2002

Surrogate light chain, which escorts the mu heavy chain to the cell surface, is a critical component of the pre-B cell receptor complex. The two proteins that comprise the surrogate light chain, VpreB and λ5/14.1, contain both unique regions and Ig-like domains. The unique regions have been postulated to function in the assembly of the surrogate light chain. However, by using transient transfection of COS7 cells, we show that deletion of the unique regions of both proteins did not inhibit the assembly of surrogate light chain. Instead,in vivofolding studies showed that the unique region of λ5/14.1 acts as an intramolecular chaperone by preventing the folding of this protein when it is expressed in the absence of its partner, VpreB. The Ig domains of both λ5/14.1 and VpreB are atypical. The one in VpreB lacks one of the canonical β strands whereas the one in λ5/14.1 has an extra β strand. Deletion of the extra β strand in λ5/14.1 completely abrogated the formation of the surrogate light chain, demonstrating that complementation of the incomplete Ig domain in VpreB by the extra β strand in λ5/14.1 was necessary and sufficient for the folding and assembly of these proteins. Our studies reveal two novel mechanisms for regulating surrogate light chain formation: (i) the presence of an intramolecular chaperone that prevents folding of the unassembled subunit but that remains part of the mature assembled protein, and (ii) splitting an Ig domain between two proteins to control their folding and assembly.
Afterglows from the largest explosions in the universe
Authors: Hartmann Dieter H.
Published: July 2002

The distinction of “largest explosions
in the universe” has been bestowed on cosmic gamma-ray bursts. Their
afterglows are brighter than supernovae and therefore are called
hypernovae. Photometry and spectroscopy of these afterglows have
provided major breakthroughs in our understanding of this mysterious
phenomenon.
Social mobility and constitutional and political preferences in Northern Ireland
Authors: Breen Richard
Published: July 2002

During the past thirty years Catholics in Northern Ireland have experienced unprecedented upward social mobility. Some commentators have suggested that this has led Catholics not merely to adopt the lifestyles of the middle class but also to modify their constitutional preferences, leading to a decline in nationalism. In this paper I examine the relationship between social mobility, on the one hand, and, on the other, both constitutional preferences and political (left or right wing) preferences among Catholics and Protestants in Northern Ireland, using survey data collected in 1996. There is no evidence that Catholics' constitutional preferences are related to their mobility experiences.