bluuebunny/crossref_metadata_2025 huggingface dataset:
Local transport barrier formation and relaxation in reverse-shear plasmas on the Tokamak Fusion Test Reactor
Authors: Synakowski E. J. , Batha S. H. , Beer M. A. , Bell M. G. , Bell R. E. , Budny R. V. , Bush C. E. , Efthimion P. C. , Hahm T. S. , Hammett G. W. , LeBlanc B. , Levinton F. , Mazzucato E. , Park H. , Ramsey A. T. , Schmidt G. , Rewoldt G. , Scott S. D. , Taylor G. , Zarnstorff M. C.
Published: July 2002

The roles of turbulence stabilization by sheared E×B flow and Shafranov shift gradients are examined for Tokamak Fusion Test Reactor [D. J. Grove and D. M. Meade, Nucl. Fusion 25, 1167 (1985)] enhanced reverse-shear (ERS) plasmas. Both effects in combination provide the basis of a positive-feedback model that predicts reinforced turbulence suppression with increasing pressure gradient. Local fluctuation behavior at the onset of ERS confinement is consistent with this framework. The power required for transitions into the ERS regime are lower when high power neutral beams are applied earlier in the current profile evolution, consistent with the suggestion that both effects play a role. Separation of the roles of E×B and Shafranov shift effects was performed by varying the E×B shear through changes in the toroidal velocity with nearly steady-state pressure profiles. Transport and fluctuation levels increase only when E×B shearing rates are driven below a critical value that is comparable to the fastest linear growth rates of the dominant instabilities. While a turbulence suppression criterion that involves the ratio of shearing to linear growth rates is in accord with many of these results, the existence of hidden dependencies of the criterion is suggested in experiments where the toroidal field was varied. The forward transition into the ERS regime has also been examined in strongly rotating plasmas. The power threshold is higher with unidirectional injection than with balance injection.
Nonlinear instability of nonhomogeneous thermal structures
Authors: Steele C. D. C. , Ibáñez S. Miguel H.
Published: July 2002

The set of families of steady state solutions of the energy equation with a heat diffusion term and a heat/loss term in a slab-like geometry have been obtained and their stability, up to the third order, analyzed by applying Landau’s method. For optically thin plasmas with solar abundances and with temperatures greater than 102 K, the kind of stability (instability) resulting for different heating mechanisms, as well as different heat diffusion laws, has been studied. In particular, the dependence of the linear rate, the second and third order Landau constants and the spatial temperature distribution of finite temperature disturbances on the degree of inhomogeneity of the initially steady state temperature distribution has been analyzed. A two parameter classification of the initially steady solutions has been obtained according to whether they show supercritical or asymptotic stability, or subcritical or superexponential instability. In general, inclusion of inhomogeneity increases the variety of cases and, in particular, those cases where the nonlinear stability is opposite to the linear stability. In many cases the second order is stable for positive perturbations, and unstable for negative perturbations, suggesting the formation of various types of condensations.
Galvanomagnetic luminescence of indium antimonide
Authors: Berdahl Paul , Shaffer Louie
Published: July 2002

We report measurements of the absolute spectral intensity due to galvanomagnetic luminescence of intrinsic InSb at room temperature. Together with a calculation of carrier and photon transport, these measurements form the basis for a new technique for the determination of carrier lifetimes and diffusion lengths. The excess carrier lifetime for InSb is found to be 6 ns, and the ambipolar diffusion length at 1.9 T is 3 μm. The spectrally integrated luminescence has a bilinear form in terms of the exciting current density  j and magnetic field B: ΔF=GB j, where ΔF is the change in the total emitted radiant energy flux from the thermal equilibrium value ( j=0). In particular ΔF can be negative. The new thermodynamic transport coefficient G has the value 1.8 μW A−1 T−1 at 33 °C and decreases with increasing temperature.
Photoluminescence of low-energy ion bombarded silicon
Authors: Davis R. J. , Habermeier H.-U. , Weber J.
Published: July 2002

Using photoluminescence we have examined defects introduced into silicon by low-energy inert gas ion bombardment (ion beam etching or ion beam milling, with Ne+, Ar+, Kr+, and Xe+) in the 200–2000 eV ion energy range. The spectra indicate the presence of noble gas associated centers which appear to be identical to the defect which is responsible for the well-known I1 spectrum (or W), except for modifications due to the interaction with the noble gas atoms. The appearance of the modified I1 spectra at these low bombardment energies suggests a simple structure of the underlying defects.
Ultrafast absorption recovery due to stimulated emission in GaAs/AlGaAs multiple quantum wells
Authors: Dubard J. , Oudar J. L. , Alexandre F. , Hulin D. , Orszag A.
Published: July 2002

Subpicosecond time-resolved absorption spectra have revealed carrier lifetimes as short as 10 ps in low-temperature GaAs/AlGaAs multiple quantum well structures (MQWS’s) due to the large stimulated recombination rate caused by amplified spontaneous luminescence guided along the MQW’s. Time-resolved detection of the edge-emitted luminescence with a streak camera fully confirms the occurrence of a fast radiative recombination associated with substantial light amplification.
Growth of α-Al2O3 films by molecular layer epitaxy
Authors: Oya Gin-ichiro , Yoshida Munehiro , Sawada Yasuji
Published: July 2002

Single-crystal α-Al2O3 films are, for the first time, successfully grown on sapphire wafers above ∼600 °C by the molecular layer epitaxy (MLE) method using AlCl3 vapor and a He 15%O2 gas mixture. The average growth rate observed barely depends on the substrate temperature, being ∼0.09 nm per cycle of gas transport, under the used growth conditions. The epitaxial growth of α-Al2O3 films on single-crystal Nb films at ∼500 °C by the MLE method is also confirmed for the first time.
GaAs growth by atomic layer epitaxy using diethylgalliumchloride
Authors: Mori Kazuo , Yoshida Masaji , Usui Akira , Terao Hiroshi
Published: July 2002

GaAs is grown by metalorganic atomic layer epitaxy (MOALE) using diethylgalliumchloride (DEGaCl) as a new MO source material for ALE and AsH3 in a horizontal, low-pressure metalorganic chemical vapor deposition system. Monolayer-unit growth has been obtained over a wide range of growth conditions, including growth temperature and the time of substrate exposure to DEGaCl. This ALE process is called ‘‘digital epitaxy,’’ and its advantages may be seen in its successful application here to extremely uniform GaAs growth on a 3-in. GaAs wafer. The digital nature of GaAs growth is well explained here using a Langmuir monolayer adsorption model for GaCl, a stable decomposition product of DEGaCl. Growth at higher temperatures leads to a reduction of carbon contamination; and at 600 °C, n-type layers with a 77 K mobility of 22 400 cm2/V s are obtained.
Chromatin immunoprecipitation analysis fails to support the latency model for regulation of p53 DNA binding activity
in
vivo
Authors: Kaeser M. D. , Iggo R. D.
Published: July 2002

p53 can adopt two forms
in vitro
, a latent
form that binds naked DNA poorly and an active form that binds DNA
well. Conversion of the latent form to the active form is
thought to occur by an allosteric mechanism induced by phosphorylation
and acetylation. Despite the large differences in affinity produced by
regulatory modifications
in vitro
, mutation of putative
regulatory sites has not produced correspondingly large effects on
transcription of p53 target genes
in vivo
. To determine
whether genotoxic stress regulates DNA binding by p53
in
vivo
, we have performed quantitative chromatin
immunoprecipitation (ChIP) assays on tumor and normal cell lines
containing wild-type p53. ChIP recovers several hundredfold more p21
and MDM2 promoter DNA from p53 wild-type than p53-null cells,
indicating that the assay is specific for p53. Genotoxic stress induces
much smaller increases in chromatin precipitation, which are matched by
changes in the p53 protein level. Thus, in the experimental systems
tested, allosteric regulation of DNA binding is not a major level of
regulation of p53 activity. The p53 target genes tested can be divided
into a group showing high promoter occupancy
in vivo
(p21, MDM2, and PUMA) and a group giving substantially weaker or
background p53 binding (bax, AIP1, and PIG3). Neither group shows
selective recruitment of p53 to the promoter in cells undergoing
apoptosis, indicating that the decision to undergo
apoptosis or cell cycle arrest depends on other changes in the
cell.
Molecular basis of R-type calcium channels in central amygdala neurons of the mouse
Authors: Lee Seung-Chan , Choi Sukwoo , Lee Taehoon , Kim Hyung-Lae , Chin Hemin , Shin Hee-Sup
Published: July 2002

R-type Ca
2+
channels play a critical role in coupling excitability to dendritic Ca
2+
influx and neuronal secretion. Unlike other types of voltage-sensitive Ca
2+
channels (L, N, P/Q, and T type), the molecular basis for the R-type Ca
2+
channel is still unclear, thereby limiting further detailed analyses of R-type Ca
2+
channel physiology. The prevailing hypothesis is that α
1E
(Ca
V
2.3) gene encodes for R-type Ca
2+
channels, but the dearth of critical evidence has rendered this hypothesis controversial. Here we generated α
1E
-deficient mice (α
1E
−/−) and examined the status of voltage-sensitive Ca
2+
currents in central amygdala (CeA) neurons that exhibit abundant α
1E
expression and R-type Ca
2+
currents. The majority of R-type currents in CeA neurons were eliminated in α
1E
−/− mice whereas other Ca
2+
channel types were unaffected. These data clearly indicate that the expression of α
1E
gene underlies R-type Ca
2+
channels in CeA neurons. Furthermore, the α
1E
−/− mice exhibited signs of enhanced fear as evidenced by their vigorous escaping behavior and aversion to open-field conditions. These latter findings imply a possible role of α
1E
-based R-type Ca
2+
currents in amygdala physiology associated with fear.
Temperature, ordering, and equilibrium with time-dependent confining forces
Authors: Schiffer J. P. , Drewsen M. , Hangst J. S. , Hornekær L.
Published: July 2002

The concepts of temperature and equilibrium are not well defined in
systems of particles with time-varying external forces. An example is a
radio frequency ion trap, with the ions laser cooled into an ordered
solid, characteristic of sub-mK temperatures, whereas the kinetic
energies associated with the fast coherent motion in the trap are up to
7 orders of magnitude higher. Simulations with 1,000 ions reach
equilibrium between the degrees of freedom when only aperiodic
displacements (secular motion) are considered. The coupling of the
periodic driven motion associated with the confinement to the
nonperiodic random motion of the ions is very small at low temperatures
and increases quadratically with temperature.
In vivo
interactions of archaeal Cdc6/Orc1 and minichromosome maintenance proteins with the replication origin
Authors: Matsunaga Fujihiko , Forterre Patrick , Ishino Yoshizumi , Myllykallio Hannu
Published: July 2002

Although genome analyses have suggested parallels between archaeal
and eukaryotic replication systems, little is known about the DNA
replication mechanism in Archaea. By two-dimensional gel
electrophoreses we positioned a replication origin
(
oriC
) within 1 kb in the chromosomal DNA of
Pyrococcus abyssi
, an anaerobic hyperthermophile, and
demonstrated that the
oriC
is physically linked to the
cdc6
gene. Our chromatin immunoprecipitation assays
indicated that
P. abyssi
Cdc6 and minichromosome
maintenance (MCM) proteins bind preferentially to the
oriC
region in the exponentially growing cells. Whereas
the
oriC
association of MCM was specifically inhibited
by stopping DNA replication with puromycin treatment, Cdc6 protein
stayed bound to the replication origin after
de novo
protein synthesis was inhibited. Our data suggest that archaeal and
eukaryotic Cdc6 and MCM proteins function similarly in replication
initiation and imply that an
oriC
association of MCM
could be regulated by an unknown mechanism in Archaea.
Congruence properties for the partition function
Authors: Ahlgren Scott , Ono Ken
Published: July 2002

Eighty years ago, Ramanujan conjectured and proved some striking congruences for the partition function modulo powers of 5, 7, and 11. Until recently, only a handful of further such congruences were known. Here we report that such congruences are much more widespread than was previously known, and we describe the theoretical framework that appears to explain every known Ramanujan-type congruence.
Position-dependent activity of α-fetoprotein enhancer element III in the adult liver is due to negative regulation
Authors: Peyton David K. , Ramesh Tennore , Spear Brett T.
Published: July 2002

α-Fetoprotein (AFP) transcription is activated early in
hepatogenesis, but is dramatically repressed within several weeks after
birth. AFP regulation is governed by multiple elements including three
enhancers termed EI, EII, and EIII. All three AFP enhancers continue to
be active in the adult liver, where EI and EII exhibit high levels of
activity in pericentral hepatocytes with a gradual reduction in
activity in a pericentral-periportal direction. In contrast to these
two enhancers, EIII activity is highly restricted to a layer of cells
surrounding the central veins. To test models that could account for
position-dependent EIII activity in the adult liver, we have analyzed
transgenes in which AFP enhancers EII and EIII were linked together.
Our results indicate that the activity of EIII is dominant over that of
EII, indicating that EIII is a potent negative regulatory element in
all hepatocytes except those encircling the central veins. We have
localized this negative activity to a 340-bp fragment. This suggests
that enhancer III may be involved in postnatal AFP repression.
Simulating pseudogene evolution
in vitro
: Determining the true number of mutations in a lineage
Authors: Vartanian Jean-Pierre , Henry Michel , Wain-Hobson Simon
Published: July 2002

Hypermutagenic PCR has been used to simulate pseudogene evolution of the
Escherichia coli
R67 dihydrofolate reductase gene. Each time the most divergent clone was used as template for another round of hypermutagenesis. After six rounds, with an average mutation rate of 0.05 per base per round, up to a 46% nucleic acid sequence variation was achieved. For a few clones the protein information content could be annihilated. As the intermediates were cloned and sequenced, it was possible to establish the real lineage and compute the true number of mutations. Not surprisingly the true number of forward and back mutations as well as variable sites exceeded those based on comparing any single intermediate to the initial sequence. However, the true number of forward and backward mutations, as well as the number of variable sites, increased linearly with sequence divergence from the original sequence, suggesting an empirical means to correct for branch lengths.
A closer look at the elementary fermions
Authors: Goldhaber Maurice
Published: July 2002

Although there have been many experimental and theoretical efforts
to measure and interpret small deviations from the standard model of
particle physics, the gap that the model leaves in understanding why
there are only three generations of the elementary fermions, with
hierarchical masses, has not received the attention it deserves.
I present here an attempt to fill this gap. Although our
findings are mostly only qualitative, they nevertheless may be of
heuristic value. Rules concerning the elementary fermions, some
previously known and some new, lead to a number of conclusions and
questions that seem worth pursuing. Some clarify the standard model,
and others suggest possible modifications, the implications of which
are discussed.
Duodenal calcium absorption in vitamin D receptor–knockout mice: Functional and molecular aspects
Authors: Van Cromphaut Sophie J. , Dewerchin Mieke , Hoenderop Joost G. J. , Stockmans Ingrid , Van Herck Erik , Kato Shigeaki , Bindels René J. M. , Collen Désiré , Carmeliet Peter , Bouillon Roger , Carmeliet Geert
Published: July 2002

Rickets and hyperparathyroidism caused by a defective vitamin D receptor (VDR) can be prevented in humans and animals by high calcium intake, suggesting that intestinal calcium absorption is critical for 1,25(OH)
2
vitamin D [1,25(OH)
2
D
3
] action on calcium homeostasis. We assessed the rate of serum
45
Ca accumulation within 10 min of oral gavage in two strains of VDR-knockout (KO) mice (Leuven and Tokyo KO) and observed a 3-fold lower area under the curve in both KO strains. Moreover, we evaluated the expression of intestinal candidate genes involved in transcellular calcium transport. The calcium transport protein1 (CaT1) was more abundantly expressed at mRNA level than the epithelial calcium channel (ECaC) in duodenum, but both were considerably reduced (CaT1>90%, ECaC>60%) in the two VDR-KO strains on a normal calcium diet. Calbindin-D
9K
expression was decreased only in the Tokyo KO, whereas plasma membrane calcium ATPase (PMCA
1b
) expression was normal in both VDR-KOs. In Leuven wild-type mice, a high calcium diet inhibited (>90%) and 1,25(OH)
2
D
3
injection or low calcium diet induced (6-fold) duodenal CaT1 expression and, to a lesser degree, ECaC and calbindin-D
9K
expression. In Leuven KO mice, however, high or low calcium intake decreased calbindin-D
9K
and PMCA
1b
expression, whereas CaT1 and ECaC expression remained consistently low on any diet. These results suggest that the expression of the novel duodenal epithelial calcium channels (in particular CaT1) is strongly vitamin D-dependent, and that calcium influx, probably interacting with calbindin-D
9K
, should be considered as a rate-limiting step in the process of vitamin D-dependent active calcium absorption.
Genetic evidence for adaptation-driven incipient speciation ofDrosophilamelanogasteralong a microclimatic contrast in “Evolution Canyon,” Israel
Authors: Michalak Pawel , Minkov Irina , Helin Amanda , Lerman Daniel N. , Bettencourt Brian R. , Feder Martin E. , Korol Abraham B. , Nevo Eviatar
Published: July 2002

Substantial genetic differentiation, as great as among species, exists between populations ofDrosophila melanogasterinhabiting opposite slopes of a small canyon. Previous work has shown that prezygotic sexual isolation and numerous differences in stress-related phenotypes have evolved betweenD. melanogasterpopulations in “Evolution Canyon,” Israel, in which slopes 100–400 m apart differ dramatically in aridity, solar radiation, and associated vegetation. Because the canyon's width is well within flies' dispersal capabilities, we examined genetic changes associated with local adaptation and incipient speciation in the absence of geographical isolation. Here we report remarkable genetic differentiation of microsatellites and divergence in the regulatory region ofhsp70Bawhich encodes the major inducible heat shock protein ofDrosophila, in the two populations. Additionally, an analysis of microsatellites suggests a limited exchange of migrants and lack of recent population bottlenecks. We hypothesize that adaptation to the contrasting microclimates overwhelms gene flow and is responsible for the genetic and phenotypic divergence between the populations.
A preference for own-subspecies' song guides vocal learning in a song bird
Authors: Nelson Douglas A.
Published: July 2002

In many song birds, males develop their songs as adults by imitating the songs of one or more tutors, memorized previously during a sensitive phase early in life. Previous work using two assays, the production of imitations by adult males and playback-induced calling by young birds during the sensitive phase for memorization, has shown that song birds can discriminate between their own and other species' songs. Herein I use both assays to show that male mountain white-crowned sparrows,Zonotrichia leucophrys oriantha, must learn to sing but have a genetic predisposition to memorize and learn the songs of their own subspecies. Playback tests to young naive birds before they even begin to sing reveal that birds give begging calls more in response toorianthasong than to songs of another species. After 10 days of tutoring with songs of either their own or another subspecies, birds continue to give stronger call responses to songs of their own subspecies, irrespective of whether they were tutored with them, and are more discriminating in distinguishing between different dialects of their own subspecies. The memory processes that facilitate recognition and discrimination of own-subspecies' song may also mediate the preferential imitation of song of a bird's own subspecies. Such perceptual biases could constrain the direction and rate of cultural evolution of learned songs.
Water-borne cues induce chemical defense in a marine alga (Ascophyllum nodosum)
Authors: Toth Gunilla B. , Pavia Henrik
Published: July 2002

It is well known that herbivores can induce chemical defenses in terrestrial vascular plants, but few examples of inducible production of defense chemicals have been reported for aquatic macrophytes. Furthermore, it is well established that water-borne chemical cues from predators or predator-wounded conspecifics can induce defensive changes of aquatic prey animals, but no such communication between aquatic herbivores and seaweeds has been reported. Here we show that water-borne cues from actively feeding herbivorous gastropods, flat periwinkles (Littorina obtusata), can serve as external signals to induce production of defense chemicals (phlorotannins) in unharmed individuals of seaweeds, knotted wrack (Ascophyllum nodosum), and that the increased levels of defense chemicals deter further feeding by periwinkles. Because seaweeds have poorly developed internal-transport systems and may not be able to elicit systemic-induced chemical defenses through conveyance of internal signals, this mechanism ensures that seaweeds can anticipate future periwinkle attacks without receiving direct damage by herbivores.
Isolation of an ovine pulmonary surfactant-associated anionic peptide bactericidal for Pasteurella haemolytica.
Authors: Brogden K A , De Lucca A J , Bland J , Elliott S
Published: July 2002

Ovine pulmonary surfactant is bactericidal for Pasteurella haemolytica when surfactant and bacteria mixtures are incubated with normal ovine serum. To isolate this component, surfactant (1 mg/ml) was centrifuged at 100,000 x gav, and the supernatant was fractionated by HPLC. Fractions were eluted with acetonitrile (10-100%)/0.1% trifluoracetic acid and tested for bactericidal activity. Amino acid and sequence analysis of three bactericidal fractions showed that fraction 2 contained H-GDDDDDD-OH, fraction 3 contained H-DDDDDDD-OH, and fraction 6 contained H-GADDDDD-OH. Peptides in 0.14 M NaCl/10 microM ZnCl2 (zinc saline solution) induced killing of P. haemolytica and other bacteria comparable to defensins and beta-defensins [minimal bactericidal concentration (MBC)50 range, 0.01-0.06 mM] but not in 0.14 M NaCl/10 mM sodium phosphate buffer, pH 7.2/0.5 mM CaCl2/0.15 mM MgCl2 (MBC50 range, 2.8-11.5 mM). Bactericidal activity resided in the core aspartate hexapeptide homopolymeric region, and MBC50 values of aspartate dipeptide-to-heptapeptide homopolymers were inversely proportional to the number of aspartate residues in the peptide. P. haemolytica incubated with H-DDDDDD-OH in zinc saline solution was killed within 30 min. Ultrastructurally, cells contained flocculated intracellular constituents. In contrast to cationic defensins and beta-defensins, surfactant-associated anionic peptides are smaller in size, opposite in charge, and are bactericidal in zinc saline solution. They are members of another class of peptide antibiotics containing aspartate, which when present in pulmonary secretions may help clear bacteria as a part of the innate pulmonary defense system.
Molecular mechanics calculations of the riboacetal internucleotide linkage in double and triple helices.
Authors: Torres R A , Almarsson O , Bruice T C
Published: July 2002

Structures of Watson-Crick base paired 15-nucleobase oligomer strands in A-type or B-type conformation in which one strand [a strand of alternating nucleotide and riboacetal thymidine nucleoside (RT) units, RP] is DNA and the other is composed of alternating nucleotides and riboacetal nucleosides have been studied by molecular mechanics. Analogously, oligomer strands of RNA in place of DNA have been modeled. The calculations indicate that the RP strand is more stable when complexed in an A-type duplex relative to a B-type form and that this conformational preference is presumably due to the more uniform nature of the former. Nearly planar ribose rings were more commonly observed in the minimized structures of the B-type DNA.RP duplexes as compared with A-type duplexes, despite the fact that planar ribofuranose rings are known to be energetically unfavorable in oligonucleotides. Computed relative stabilities of all duplexes containing the RP strand suggest that such heteroduplexes are less stable than the corresponding double-stranded DNA and double-stranded RNA species. These findings are in agreement with experimental results which show, when equivalent sequences were compared, that a DNA.RNA control forms a more stable duplex than RP hound to a complementary single-stranded RNA strand. In contrast, molecular mechanics studies of complementary triple-helical (DNA)2.RP, (DNA)2.DNA, and (DNA)2.RNA structures indicate that the binding of RP as a Hoogsteen strand stabilizes the underlying duplex to a greater extent compared with native oligonucleotides. These calculations suggest that puckering of the ribose ring in the riboacetal linkage leads to a more favorable interaction with a complementary nucleic acid target than the proposed planar geometry and that this puckering may account for the enhanced binding of RP to a double-stranded target.
Cellular mechanisms for the formation of a soluble form derivative of T-cell receptor alpha chain by suppressor T cells.
Authors: Ishii Y , Nakano T , Ishizaka K
Published: July 2002

Upon stimulation with anti-CD3, suppressor T-cell (Ts) hybridomas and homologous transfectants of T-cell receptor a (TCRalpha) cDNA in the T-cell hybridoma formed a 55-kDa TCRalpha chain derivative that bound both the monoclonal anti-TCRalpha chain and polyclonal antibodies against glycosylation inhibiting factor (GIF). The peptide is a subunit of antigen-specific suppressor T-cell factor (TsF), and is considered to be a posttranslationally-formed conjugate of TCRalpha chain with GIF peptide. The TCRalpha derivative is synthesized by the transfectant after stimulation with anti-CD3, and not derived from TCR present on the cell surface. Stimulation of the stable homologous transfectants with anti-CD3 induced translocation of the 13-kDa GIF peptide into endoplasmic reticulum (ER). When a helper Ts hybridoma or a stable transfectant of the same TCRalpha cDNA in a helper cell-derived TCRalpha- clone was stimulated with anti-CD3, translocation of GIF peptide was not detected, and these cells failed to secrete a TCRalpha derivative. However, further transfection of a chimeric cDNA encoding a procalcitonin-GIF fusion protein into the helper cell-derived stable transfectant of TCRalpha cDNA resulted in translocation of the GIF protein and formation of bioactive 55-kDa GIF. The results indicated that translocation of GIF peptide through ER is unique for Ts cells, and that this process is essential for the formation/secretion of the soluble form derivative of TCRalpha chain by T cells.
Isolation and characterization of mutant cell lines defective in transforming growth factor beta signaling.
Authors: Hocevar B A , Howe P H
Published: July 2002

To isolate and characterize effector molecules of the transforming growth factor beta (TGFbeta) signaling pathway we have used a genetic approach involving the generation of stable recessive mutants, defective in their TGFbeta signaling, which can subsequently be functionally complemented to clone the affected genes. We have generated a cell line derived from a hypoxanthine-guanine phosphoribosyltransferase negative (HPRT-) HT1080 clone that contains the selectable marker Escherichia coli guanine phosphoribosyltransferase (gpt) linked to a TGFbeta-responsive promoter. This cell line proliferates or dies in the appropriate selection medium in response to TGFbeta. We have isolated three distinct TGFbeta-unresponsive mutants following chemical mutagenesis. Somatic cell hybrids between pairs of individual TGFbeta-unresponsive clones reveal that each is in a distinct complementation group. Each mutant clone retains all three TGFbeta receptors yet fails to induce a TGFbeta-inducible luciferase reporter construct or TGFbeta-mediated plasminogen activator inhibitor-1 (PAI-1) expression. Two of the three have an attenuated TGFbeta-induced fibronectin response, whereas in the other mutant the fibronectin response is intact. These TGFbeta-unresponsive cells should allow selection and identification of signaling molecules through functional complementation.
The full-length leptin receptor has signaling capabilities of interleukin 6-type cytokine receptors.
Authors: Baumann H , Morella K K , White D W , Dembski M , Bailon P S , Kim H , Lai C F , Tartaglia L A
Published: July 2002

The leptin receptor (OB-R) is a single membrane-spanning protein that mediates the weight regulatory effects of leptin (OB protein). The mutant allele (db) of the OB-R gene encodes a protein with a truncated cytoplasmic domain that is predicted to be functionally inactive. Several mRNA splice variants encoding OB-Rs with different length cytoplasmic domains have been detected in various tissues. Here we demonstrate that the full-length OB-R (predominantly expressed in the hypothalamus), but not a major naturally occurring truncated form or a mutant from found in db/db mice, can mediate activation of signal transducer and activator of transcription (STAT) proteins and stimulate transcription through interleukin 6 responsive gene elements. Reconstitution experiments suggest that, although OB-R mediates intracellular signals with a specificity similar to interleukin 6-type cytokine receptors, signaling appears to be independent of the gp130 signal transducing component of the interleukin 6-type cytokine receptors.
Glutathione-mediated destabilization in vitro of [2Fe-2S] centers in the SoxR regulatory protein.
Authors: Ding H , Demple B
Published: July 2002

SoxR is a transcription factor that governs a global defense against the oxidative stress caused by nitric oxide or excess superoxide in Escherichia coli. SoxR is a homodimer containing a pair of [2Fe-2S] clusters essential for its transcriptional activity, and changes in the stability of these metal centers could contribute to the activation or inactivation of SoxR in vivo. Herein we show that reduced glutathione (GSH) in aerobic solution disrupts the SoxR [2Fe-2S] clusters, releasing Fe from the protein and eliminating SoxR transcriptional activity. This disassembly process evidently involves oxygen-derived free radicals. The loss of [2Fe-2S] clusters does not occur in anaerobic solution and is blocked in aerobic solution by the addition of superoxide dismutase and catalase. Although H2O2 or xanthine oxidase and hypoxanthine (to generate superoxide) were insufficient on their own to cause [2Fe-2S] cluster loss, they did accelerate the rate of disassembly after GSH addition. Oxidized GSH alone was ineffective in disrupting the clusters, but the rate of [2Fe-2S] cluster disassembly was maximal when reduced and oxidized GSH were present at a ratio of approximately 1:3, which suggests the critical involvement of a GSH-based free radical in the disassembly process. Such a reaction might occur in vivo: we found that the induction by paraquat of SoxR-dependent soxS transcription was much higher in a GSH-deficient E. coli strain than in its GSH-containing parent. The results imply that GSH may play a significant role during the deactivation process of SoxR in vivo. Ironically, superoxide production seems both to activate SoxR and, in the GSH-dependent disassembly process, to switch off this transcription factor.
Apoptosis mediated by HIV protease is preceded by cleavage of Bcl-2.
Authors: Strack P R , Frey M W , Rizzo C J , Cordova B , George H J , Meade R , Ho S P , Corman J , Tritch R , Korant B D
Published: July 2002

Expression of the human immunodeficiency virus type 1 (HIV) protease in cultured cells leads to apoptosis, preceded by cleavage of bcl-2, a key negative regulator of cell death. In contrast, a high level of bcl-2 protects cells in vitro and in vivo from the viral protease and prevents cell death following HIV infection of human lymphocytes, while reducing the yields of viral structural proteins, infectivity, and tumor necrosis factor alpha. We present a model for HIV replication in which the viral protease depletes the infected cells of bcl-2, leading to oxidative stress-dependent activation of NF kappa B, a cellular factor required for HIV transcription, and ultimately to cell death. Purified bcl-2 is cleaved by HIV protease between phenylalanine 112 and alanine 113. The results suggest a new option for HIV gene therapy; bcl-2 muteins that have noncleavable alterations surrounding the HIV protease cleavage site.
Foreign glycoproteins expressed from recombinant vesicular stomatitis viruses are incorporated efficiently into virus particles.
Authors: Schnell M J , Buonocore L , Kretzschmar E , Johnson E , Rose J K
Published: July 2002

In a previous study we demonstrated that vesicular stomatitis virus (VSV) can be used as a vector to express a soluble protein in mammalian cells. Here we have generated VSV recombinants that express four different membrane proteins: the cellular CD4 protein, a CD4-G hybrid protein containing the ectodomain of CD4 and the transmembrane and cytoplasmic tail of the VSV glycoprotein (G), the measles virus hemagglutinin, or the measles virus fusion protein. The proteins were expressed at levels ranging from 23-62% that of VSV G protein and all were transported to the cell surface. In addition we found that all four proteins were incorporated into the membrane envelope of VSV along with the VSV G protein. The levels of incorporation of these proteins varied from 6-31% of that observed for VSV G. These results suggest that many different membrane proteins may be co-incorporated quite efficiently with VSV G protein into budding VSV virus particles and that specific signals are not required for this co-incorporation process. In fact, the CD4-G protein was incorporated with the same efficiency as wild type CD4. Electron microscopy of virions containing CD4 revealed that the CD4 molecules were dispersed throughout the virion envelope among the trimeric viral spike glycoproteins. The recombinant VSV-CD4 virus particles were about 18% longer than wild type virions, reflecting the additional length of the helical nucleocapsid containing the extra gene. Recombinant VSVs carrying foreign antigens on the surface of the virus particle may be useful for viral targeting, membrane protein purification, and for generation of immune responses.
Real time observation of anaphase in vitro.
Authors: Murray A W , Desai A B , Salmon E D
Published: July 2002

We used digital fluorescence microscopy to make real-time observations of anaphase chromosome movement and changes in microtubule organization in spindles assembled in Xenopus egg extracts. Anaphase chromosome movement in these extracts resembled that seen in living vertebrate cells. During anaphase chromosomes moved toward the spindle poles (anaphase A) and the majority reached positions very close to the spindle poles. The average rate of chromosome to pole movement (2.4 microns/min) was similar to earlier measurements of poleward microtubule flux during metaphase. An increase in pole-to-pole distance (anaphase B) occurred in some spindles. The polyploidy of the spindles we examined allowed us to observe two novel features of mitosis. First, during anaphase, multiple microtubule organizing centers migrated 40 microns or more away from the spindle poles. Second, in telophase, decondensing chromosomes often moved rapidly (7-23 microns/min) away from the spindle poles toward the centers of these asters. This telophase chromosome movement suggests that the surface of decondensing chromosomes, and by extension those of intact nuclei, bear minus-end-directed microtubule motors. Preventing the inactivation of Cdc2/cyclin B complexes by adding nondegradable cyclin B allowed anaphase A to occur at normal velocities, but reduced the ejection of asters from the spindles, blocked chromosome decondensation, and inhibited telophase chromosome movement. In the presence of nondegradable cyclin B, chromosome movement to the poles converted bipolar spindles into pairs of independent monopolar spindles, demonstrating the role of sister chromatid linkage in maintaining spindle bipolarity.
Flowers into shoots: Photo and hormonal control of a meristem identity switch in Arabidopsis
Authors: Okamuro Jack K. , den Boer Bart G. W. , Lotys-Prass Cynthia , Szeto Wayne , Jofuku K. Diane
Published: July 2002

Little is known about the signals that govern the network of
meristem and organ identity genes that control flower development. In
Arabidopsis
, we can induce a heterochronic switch from
flower to shoot development, a process known as floral meristem
reversion, by manipulating photoperiod in the floral homeotic mutant
agamous
and in plants heterozygous for the meristem
identity gene
leafy
. The transformation from flower to
shoot meristem is suppressed by
hy1
, a mutation blocking
phytochrome activity, by
spindly
, a mutation that
activates basal gibberellin signal transduction in a hormone
independent manner, or by the exogenous application of gibberellins. We
propose that
LFY
and
AG
play an important
role in the maintenance of flower meristem identity and that floral
meristem reversion in heterozygous
lfy
and in
ag
flowers is regulated by a phytochrome and gibberellin
signal transduction cascade.
Effect of age onin vivorates of mitochondrial protein synthesis in human skeletal muscle
Authors: Rooyackers Olav E. , Adey Deborah B. , Ades Philip A. , Nair K. Sreekumaran
Published: July 2002

A progressive decline in muscle performance in the rapidly expanding aging population is causing a dramatic increase in disability and health care costs. A decrease in muscle endurance capacity due to mitochondrial decay likely contributes to this decline in muscle performance. We developed a novel stable isotope technique to measurein vivorates of mitochondrial protein synthesis in human skeletal muscle using needle biopsy samples and applied this technique to elucidate a potential mechanism for the age-related decline in the mitochondrial content and function of skeletal muscle. The fractional rate of muscle mitochondrial protein synthesis in young humans (24 ± 1 year) was 0.081 ± 0.004%·h−1, and this rate declined to 0.047 ± 0.005%·h−1by middle age (54 ± 1 year;P< 0.01). No further decline in the rate of mitochondrial protein synthesis (0.051 ± 0.004%·h−1) occurred with advancing age (73 ± 2 years). The mitochondrial synthesis rate was about 95% higher than that of mixed protein in the young, whereas it was approximately 35% higher in the middle-aged and elderly subjects. In addition, decreasing activities of mitochondrial enzymes were observed in muscle homogenates (cytochromecoxidase and citrate synthase) and in isolated mitochondria (citrate synthase) with increasing age, indicating declines in muscle oxidative capacity and mitochondrial function, respectively. The decrease in the rates of mitochondrial protein synthesis is likely to be responsible for this decline in muscle oxidative capacity and mitochondrial function. These changes in muscle mitochondrial protein metabolism may contribute to the age-related decline in aerobic capacity and muscle performance.
The human lysozyme promoter directs reporter gene expression to activated myelomonocytic cells in transgenic mice.
Authors: Clarke S , Greaves D R , Chung L P , Tree P , Gordon S
Published: July 2002

The 5' region of the human lysozyme gene from -3500 to +25 was fused to a chloramphenicol acetyltransferase (CAT) reporter gene and three transgenic founder mice were obtained. All three transgenic lines showed the same pattern of CAT enzyme expression in adult mouse tissues that was consistent with the targeting of elicited, activated macrophages in tissues and developing and elicited granulocytes. In normal mice high CAT enzyme activity was found in the spleen, lung, and thymus, tissues rich in phagocytically active cells, but not in many other tissues, such as the gut and muscle, which contain resident macrophages. Cultured resident peritoneal macrophages and cells elicited 18 hr (granulocytes) and 4 days (macrophages) after injection of sterile thioglycollate broth expressed CAT activity. Bacillus Calmette-Guérin infection of transgenic mice resulted in CAT enzyme expression in the liver, which contained macrophage-rich granulomas, whereas the liver of uninfected mice did not have any detectable CAT enzyme activity. Although the Paneth cells of the small intestine in both human and mouse produce lysozyme, the CAT gene, under the control of the human lysozyme promoter, was not expressed in the mouse small intestine. These results indicate that the human lysozyme promoter region may be used to direct expression of genes to activated mouse myeloid cells.
L
p

estimates for the bilinear Hilbert transform
Authors: Lacey Michael , Thiele Christoph
Published: July 2002

For the bilinear Hilbert transform given by:

\documentclass[12pt]{minimal}
\usepackage{amsmath}
\usepackage{wasysym}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{amsbsy}
\usepackage{mathrsfs}
\setlength{\oddsidemargin}{-69pt}
\begin{document}
\begin{equation*}{\mathit{H\hspace{.167em}fg}}({\mathit{x}}){\mathrm{\hspace{.167em}=\hspace{.167em}p.v.}}{\int }{\mathit{f}}({\mathit{x\hspace{.167em}-\hspace{.167em}y}}){\mathit{g}}({\mathit{x\hspace{.167em}+\hspace{.167em}y}}){\mathrm{\hspace{.167em}}}\frac{{\mathit{dy}}}{{\mathit{y}}}{\mathrm{,}}\end{equation*}\end{document}

we
announce the inequality ∥
H
fg
∥

p
3

≤
K

p
1

,
p
2

∥
f
∥

p
1

∥
g
∥

p
2

,
provided 2 <
p
1
,
p
2
< ∞, 1/
p
3
= 1/
p
1
+
1/
p
2
and 1 <
p
3
< 2.
Molecular origin of the mosaic sequence arrangements of higher primate α-globin duplication units
Authors: Bailey Arnold D. , Shen Chien Celia , Shen Che-Kun James
Published: July 2002

The human adult α-globin locus consists of three pairs of homology blocks (X, Y, and Z) interspersed with three nonhomology blocks (I, II, and III), and three
Alu
family repeats,
Alu1, Alu2
, and
Alu3
. It has been suggested that an ancient primate α-globin-containing unit was ancestral to the X, Y, and Z and the
Alu1/Alu2
repeats. However, the evolutionary origin of the three nonhomologous blocks has remained obscure. We have now analyzed the sequence organization of the entire adult α-globin locus of gibbon (
Hylobates lar
). DNA segments homologous to human block I occur in both duplication units of the gibbon α-globin locus. Detailed interspecies sequence comparisons suggest that nonhomologous blocks I and II, as well as another sequence, IV, were all part of the ancestral α-globin-containing unit prior to its tandem duplication. However, sometime thereafter, block I was deleted from the human α1-globin-containing unit, and block II was also deleted from the α2-globin-containing unit in both human and gibbon. These were probably independent events both mediated by independent illegitimate recombination processes. Interestingly, the end points of these deletions coincide with potential insertion sites of
Alu
family repeats. These results suggest that the shaping of DNA segments in eukaryotic genomes involved the retroposition of repetitive DNA elements in conjunction with simple DNA recombination processes.
Novel isoforms of the β and γ subunits of the
Xenopus
epithelial Na channel provide information about the amiloride binding site and extracellular sodium sensing
Authors: Puoti Alessandro , May Anne , Rossier Bernard C. , Horisberger Jean-Daniel
Published: July 2002

We have previously identified three homologous subunits α, β, and γ of the highly selective amiloride-sensitive Na channel from the
Xenopus laevis
kidney A6 cell line, which forms a tight epithelium in culture. We report here two novel genes, termed β2 and γ2, which share 90 and 92% sequence identity with the previously characterized β and γ XENaC, respectively. β2 and γ2 transcripts were detected in lung, kidney, and A6 cells grown on porous substrate. The physiological and pharmacological profile of the Na channel expressed after αβ2γ XENaC cRNA injection in
Xenopus
oocyte did not differ from αβγ XENaC. By contrast, the channel expressed after αβγ2 injection showed: (
i
) a lower maximal amiloride-sensitive sodium current, (
ii
) a higher apparent affinity for external sodium and inactivation of the sodium current by high sodium concentrations, and (
iii
) a lower apparent affinity for amiloride (
K
I
αβγ2; 1.34 μM versus αβγ 0.35 μM). These data indicate that the γ (and/or γ2) subunit participates in amiloride binding and the sensing of the extracellular sodium concentration. The close homology between γ and γ2 will help to define the domains involved in sensing external sodium and in the structure of this important drug receptor.
Acquisition and amplification of a testis-expressed autosomal gene,SSL, by theDrosophilaY chromosome
Authors: Kalmykova Alla I. , Shevelyov Yury Y. , Dobritsa Anna A. , Gvozdev Vladimir A.
Published: July 2002

The acquisition of autosomal fertility genes has been proposed to be an important process in human Y chromosome evolution. For example, the Y-linked fertility factorDAZ(Deleted in Azoospermia) appears to have arisen after the transposition and tandem amplification of the autosomalDAZHgene. TheDrosophila melanogasterY chromosome contains tandemly repeatedSu(Ste)units that are thought to affect male fertility as suppressors of the homologous X-linkedStellaterepeats. Here we report the detection of a testis-expressed autosomal gene,SSL[Su(Ste)-like], that appears to be an ancestor of the Y-linkedSu(Ste)units.SSLencodes a casein kinase 2 (CK2)β-subunit-like protein. Its putative ORF shares extensive (45%) homology with the genuineβ-subunit of CK2 and retains the conserved C-terminal and Glu/Asp-rich domains that are essential for CK2 holoenzyme regulation.SSLmaps within region 60D1–2 ofD. melanogasterandD. simulanspolytene chromosomes. We present evidence thatSSLwas derived from the genuineβCK2 gene by reverse transcription. This event resulted in the loss of the first three introns in the coding region of theSSLancestor gene. Evolutionary analysis indicates thatSSLhas evolved under selective pressure at the translational level. Its sequence, especially in the 3′ region, is much closer to the Y-linkedSu(Ste)tandem repeats than to theβCK2 gene. These results suggest that the acquisition of testis-specific autosomal genes may be important for the evolution ofDrosophilaas well as human Y chromosomes.