bluuebunny/crossref_metadata_2025 huggingface dataset:
Genetic Discrimination: Perspectives of Consumers
Authors: Lapham E. Virginia , Kozma Chahira , Weiss Joan O.
Published: July 2002

In a study of the perceptions of 332 members of genetic support groups with one or more of 101 different genetic disorders in the family, it was found that as a result of a genetic disorder 25 percent of the respondents or affected family members believed they were refused life insurance, 22 percent believed they were refused health insurance, and 13 percent believed they were denied or let go from a job. Fear of genetic discrimination resulted in 9 percent of respondents or family members refusing to be tested for genetic conditions, 18 percent not revealing genetic information to insurers, and 17 percent not revealing information to employers. The level of perceived discrimination points to the need for more information to determine the extent and scope of the problem.
Chaperone Function of Hsp90-Associated Proteins
Authors: Bose Suchira , Weikl Tina , Bügl Hans , Buchner Johannes
Published: July 2002

The Hsp90 heat shock protein of eukaryotic cells regulates the activity of proteins involved in signal transduction pathways and may direct intracellular protein folding in general. Hsp90 performs at least part of its function in a complex with a specific set of partner proteins that include members of the prolyl isomerase family. The properties of the major components of the Hsp90 complex were examined through the use of in vitro protein folding assays. Two of the components, FKBP52 and p23, functioned as mechanistically distinct molecular chaperones. These results suggest the existence of a super-chaperone complex in the cytosol of eukaryotic cells.
A Role for Endothelial NO Synthase in LTP Revealed by Adenovirus-Mediated Inhibition and Rescue
Authors: Kantor David B. , Lanzrein Markus , Stary S. Jennifer , Sandoval Gisela M. , Smith W. Bryan , Sullivan Brian M. , Davidson Norman , Schuman Erin M.
Published: July 2002

Pharmacological studies support the idea that nitric oxide (NO) serves as a retrograde messenger during long-term potentiation (LTP) in area CA1 of the hippocampus. Mice with a defective form of the gene for neuronal NO synthase (nNOS), however, exhibit normal LTP. The myristoyl protein endothelial NOS (eNOS) is present in the dendrites of CA1 neurons. Recombinant adenovirus vectors containing either a truncated eNOS (a putative dominant negative) or an eNOS fused to a transmembrane protein were used to demonstrate that membrane-targeted eNOS is required for LTP. The membrane localization of eNOS may optimally position the enzyme both to respond to Ca
2+
influx and to release NO into the extracellular space during LTP induction.
Global Climate and Infectious Disease: The Cholera Paradigm
Authors: Colwell Rita R.
Published: July 2002

The origin of cholera has been elusive, even though scientific evidence clearly shows it is a waterborne disease. However, standard bacteriological procedures for isolation of the cholera vibrio from environmental samples, including water, between epidemics generally were unsuccessful.
Vibrio cholerae
, a marine vibrio, requiring salt for growth, enters into a dormant, viable but nonculturable stage when conditions are unfavorable for growth and reproduction. The association of
Vibrio cholerae
with plankton, notably copepods, provides further evidence for the environmental origin of cholera, as well as an explanation for the sporadic and erratic occurrence of cholera epidemics. On a global scale, cholera epidemics can now be related to climate and climatic events, such as El Niño, as well as the global distribution of the plankton host. Remote sensing, with the use of satellite imagery, offers the potential for predicting conditions conducive to cholera outbreaks or epidemics.
Evidence for the Conformation of the Pathologic Isoform of the Prion Protein Enciphering and Propagating Prion Diversity
Authors: Telling Glenn C. , Parchi Piero , DeArmond Stephen J. , Cortelli Pietro , Montagna Pasquale , Gabizon Ruth , Mastrianni James , Lugaresi Elio , Gambetti Pierluigi , Prusiner Stanley B.
Published: July 2002

The fundamental event in prion diseases seems to be a conformational change in cellular prion protein (PrP
C
) whereby it is converted into the pathologic isoform PrP
Sc
. In fatal familial insomnia (FFI), the protease-resistant fragment of PrP
Sc
after deglycosylation has a size of 19 kilodaltons, whereas that from other inherited and sporadic prion diseases is 21 kilodaltons. Extracts from the brains of FFI patients transmitted disease to transgenic mice expressing a chimeric human-mouse PrP gene about 200 days after inoculation and induced formation of the 19-kilodalton PrP
Sc
fragment, whereas extracts from the brains of familial and sporadic Creutzfeldt-Jakob disease patients produced the 21-kilodalton PrP
Sc
fragment in these mice. The results presented indicate that the conformation of PrP
Sc
functions as a template in directing the formation of nascent PrP
Sc
and suggest a mechanism to explain strains of prions where diversity is encrypted in the conformation of PrP
Sc
.
Polymorphic Phase Transitions in Liquids and Glasses
Authors: Poole Peter H. , Grande Tor , Angell C. Austen , McMillan Paul F.
Published: July 2002

Fluids such as liquids and glasses are not usually thought of as possessing distinct forms or phases. As Poole
et al
. discuss in their Perspective, recent results show that liquids can exhibit “polymorphism”—different phases characterized by different densities.
How Cells Get the Right Chromosomes
Authors: Nicklas R. Bruce
Published: July 2002

When cells divide, the chromosomes must be delivered flawlessly to the daughter cells. Missing or extra chromosomes can result in birth defects and cancer. Chance events are the starting point for chromosome delivery, which makes the process prone to error. Errors are avoided by diverse uses of mechanical tension from mitotic forces. Tension stabilizes the proper chromosome configuration, controls a cell cycle checkpoint, and changes chromosome chemistry.
Dopaminergic Neurons Protected from Degeneration by GDNF Gene Therapy
Authors: Choi-Lundberg Derek L. , Lin Qing , Chang Yung-Nien , Chiang Yawen L. , Hay Carl M. , Mohajeri Hasan , Davidson Beverly L. , Bohn Martha C.
Published: July 2002

Glial cell line-derived neurotrophic factor (GDNF) supports growth and survival of dopaminergic (DA) neurons. A replication-defective adenoviral (Ad) vector encoding human GDNF injected near the rat substantia nigra was found to protect DA neurons from the progressive degeneration induced by the neurotoxin 6-hydroxydopamine (6-OHDA) injected into the striatum. Ad GDNF gene therapy reduced loss of DA neurons approximately threefold 6 weeks after 6-OHDA lesion, as compared with no treatment or injection of Ad lacZ or Ad mGDNF (encoding a biologically inactive deletion mutant GDNF). These results suggest that Ad vector-mediated GDNF gene therapy may slow the DA neuronal cell loss in humans with Parkinson's disease.
Genetic Information and the Workplace: Legislative Approaches and Policy Challenges
Authors: Rothenberg Karen , Fuller Barbara , Rothstein Mark , Duster Troy , Kahn Mary Jo Ellis , Cunningham Rita , Fine Beth , Hudson Kathy , King Mary-Claire , Murphy Patricia , Swergold Gary , Collins Francis
Published: July 2002

The use of genetic information in the workplace poses societal risks that have an impact on employment possibilities, health insurance, and privacy. Individuals who might otherwise believe they can benefit from genetic testing may decline it because of their fear of employment discrimination and lack of privacy in the workplace. As a consequence, the future of research on the benefits and risks of predictive genetic testing may also be compromised. Thus, policy-makers need to evaluate legislative and regulatory strategies to address these concerns. This paper analyzes state and federal legislative approaches to genetic information in the workplace and concludes with a discussion of policy considerations and recommendation.
Single-Electron Transport in Ropes of Carbon Nanotubes
Authors: Bockrath Marc , Cobden David H. , McEuen Paul L. , Chopra Nasreen G. , Zettl A. , Thess Andreas , Smalley R. E.
Published: July 2002

The electrical properties of individual bundles, or “ropes,” of single-walled carbon nanotubes have been measured. Below about 10 kelvin, the low-bias conductance was suppressed for voltages less than a few millivolts. In addition, dramatic peaks were observed in the conductance as a function of a gate voltage that modulated the number of electrons in the rope. These results are interpreted in terms of single-electron charging and resonant tunneling through the quantized energy levels of the nanotubes composing the rope.
Separate Neural Bases of Two Fundamental Memory Processes in the Human Medial Temporal Lobe
Authors: Gabrieli John D. E. , Brewer James B. , Desmond John E. , Glover Gary H.
Published: July 2002

The participation of medial temporal-lobe structures in memory performance was examined by functional magnetic resonance imaging of local blood oxygenation level–dependent signals. Signals were measured during encoding into memory complex scenes or line drawings and during retrieval from memory of previously studied line drawings or words. Encoding tasks yielded increased signals for unfamiliar information in a posterior medial-temporal region that were focused in the parahippocampal cortex. Retrieval tasks yielded increased signals for successfully remembered information in an anterior medial-temporal region that were focused in the subiculum. These results indicate that separate components of the human medial temporal-lobe memory system are active during distinct memory processes.
Size Dependence of Structural Metastability in Semiconductor Nanocrystals
Authors: Chen Chia-Chun , Herhold A. B. , Johnson C. S. , Alivisatos A. P.
Published: July 2002

The kinetics of a first-order, solid-solid phase transition were investigated in the prototypical nanocrystal system CdSe as a function of crystallite size. In contrast to extended solids, nanocrystals convert from one structure to another by single nucleation events, and the transformations obey simple unimolecular kinetics. Barrier heights were observed to increase with increasing nanocrystal size, although they also depend on the nature of the nanocrystal surface. These results are analogous to magnetic phase transitions in nanocrystals and suggest general rules that may be of use in the discovery of new metastable phases.
Ndj1p, a Meiotic Telomere Protein Required for Normal Chromosome Synapsis and Segregation in Yeast
Authors: Conrad Michael N. , Dominguez Ana M. , Dresser Michael E.
Published: July 2002

The
Saccharomyces cerevisiae
gene
NDJ1
(nondisjunction) encodes a protein that accumulates at telomeres during meiotic prophase. Deletion of
NDJ1
(
ndj1Δ
) caused nondisjunction, impaired distributive segregation of linear chromosomes, and disordered the distribution of telomeric Rap1p, but it did not affect distributive segregation of circular plasmids. Induction of meiotic recombination and the extent of crossing-over were largely normal in
ndj1Δ
cells, but formation of axial elements and synapsis were delayed. Thus, Ndj1p may stabilize homologous DNA interactions at telomeres, and possibly at other sites, and it is required for a telomere activity in distributive segregation.
A Hominid from the Lower Pleistocene of Atapuerca, Spain: Possible Ancestor to Neandertals and Modern Humans
Authors: Bermúdez de Castro J. M. , Arsuaga J. L. , Carbonell E. , Rosas A. , Martı́nez I. , Mosquera M.
Published: July 2002

Human fossil remains recovered from the TD6 level (Aurora stratum) of the lower Pleistocene cave site of Gran Dolina, Sierra de Atapuerca, Spain, exhibit a unique combination of cranial, mandibular, and dental traits and are suggested as a new species of
Homo—H. antecessor
sp. nov. The fully modern midfacial morphology of the fossils antedates other evidence of this feature by about 650,000 years. The midfacial and subnasal morphology of modern humans may be a retention of a juvenile pattern that was not yet present in
H. ergaster. Homo antecessor
may represent the last common ancestor for Neandertals and modern humans.
Arecibo Radar Mapping of the Lunar Poles: A Search for Ice Deposits
Authors: Stacy N. J. S. , Campbell D. B. , Ford P. G.
Published: July 2002

The Arecibo 12.6-centimeter wavelength radar system was used to image the polar regions of the moon at a resolution of 125 meters in a search for ice deposits in areas of possible permanent shadow from the sun. No areas greater than 1 square kilometer were found with high radar backscatter cross sections and high circular polarization ratios, properties suggestive of the presence of ice. A number of areas smaller than 1 square kilometer were found with these properties, but optical images from spacecraft missions have shown some of these features to be in sunlight. Arecibo radar images of Sinus Iridum at latitude 47°N also showed a number of small features with similar properties. The coincidence of some of these features with the radar-facing slopes of craters and their presence in sunlit areas suggests that very rough surfaces rather than ice deposits are responsible for their unusual radar properties.
A Disk of Scattered Icy Objects and the Origin of Jupiter-Family Comets
Authors: Duncan Martin J. , Levison Harold F.
Published: July 2002

Orbital integrations carried out for 4 billion years produced a disk of scattered objects beyond the orbit of Neptune. Objects in this disk can be distinguished from Kuiper belt objects by a greater range of eccentricities and inclinations. This disk was formed in the simulations by encounters with Neptune during the early evolution of the outer solar system. After particles first encountered Neptune, the simulations show that about 1 percent of the particles survive in this disk for the age of the solar system. A disk currently containing as few as ∼6 × 10
8
objects could supply all of the observed Jupiter-family comets. Two recently discovered objects, 1996 RQ
20
and 1996 TL
66
, have orbital elements similar to those predicted for objects in this disk, suggesting that they are thus far the only members of this disk to be identified.
Chlorine-36 in Fossil Rat Urine: An Archive of Cosmogenic Nuclide Deposition During the Past 40,000 Years
Authors: Plummer Mitchell A. , Phillips Fred M. , Fabryka-Martin June , Turin H. J. , Wigand Peter E. , Sharma Pankaj
Published: July 2002

Knowledge of the production history of cosmogenic nuclides, which is needed for geological and archaeological dating, has been uncertain. Measurements of chlorine-36/chlorine (
36
Cl/Cl) ratios in fossil packrat middens from Nevada that are radiocarbon-dated between about 38 thousand years ago (ka) and the present showed that
36
Cl/Cl ratios were higher by a factor of about 2 before ∼11 ka. This raises the possibility that cosmogenic production rates just before the close of the Pleistocene were up to 50% higher than is suggested by carbon-14 calibration data. The discrepancy could be explained by addition of low–carbon-14 carbon dioxide to the atmosphere during that period, which would have depressed atmospheric radiocarbon activity. Alternatively, climatic effects on
36
Cl deposition may have enhanced the
36
Cl/Cl ratios.
Holistic Cosmology
Authors: Silk Joseph
Published: July 2002

The Life of the Cosmos.
LEE SMOLIN. Oxford University Press, New York, 1997. viii, 358 pp., illus. $30. ISBN 0-19-510837-x. Published in the UK by Weidenfeld and Nicolson; £20, ISBN 0-297-81727-2.
A Test Case of Correlation Metric Construction of a Reaction Pathway from Measurements
Authors: Arkin Adam , Shen Peidong , Ross John
Published: July 2002

A method for the prediction of the interactions within complex reaction networks from experimentally measured time series of the concentration of the species composing the system has been tested experimentally on the first few steps of the glycolytic pathway. The reconstituted reaction system, containing eight enzymes and 14 metabolic intermediates, was kept away from equilibrium in a continuous-flow, stirred-tank reactor. Input concentrations of adenosine monophosphate and citrate were externally varied over time, and their concentrations in the reactor and the response of eight other species were measured. Multidimensional scaling analysis and heuristic algorithms applied to two-species time-lagged correlation functions derived from the time series yielded a diagram from which the interactions among all of the species could be deduced. The diagram predicts essential features of the known reaction network in regard to chemical reactions and interactions among the measured species. The approach is applicable to many complex reaction systems.
The Importance of Recent Ice Ages in Speciation: A Failed Paradigm
Authors: Klicka John , Zink Robert M.
Published: July 2002

Late Pleistocene glaciations have been ascribed a dominant role in sculpting present-day diversity and distributions of North American vertebrates. Molecular comparisons of recently diverged sister species now permit a test of this assertion. The Late Pleistocene Origins model predicts a mitochondrial DNA divergence value of less than 0.5 percent for avian sister species of Late Pleistocene origin. Instead, the average mitochondrial DNA sequence divergence for 35 such songbird species pairs is 5.1 percent, which exceeds the predicted value by a factor of 10. Molecular data suggest a relatively protracted history of speciation events among North American songbirds over the past 5 million years.
V(D)J Recombination in Mature B Cells: A Mechanism for Altering Antibody Responses
Authors: Papavasiliou Fotini , Casellas Rafael , Suh Heikyung , Qin Xiao-Feng , Besmer Eva , Pelanda Roberta , Nemazee David , Rajewsky Klaus , Nussenzweig Michel C.
Published: July 2002

The clonal selection theory states that B lymphocytes producing high-affinity immunoglobulins are selected from a pool of cells undergoing antibody gene mutation. Somatic hypermutation is a well-documented mechanism for achieving diversification of immune responses in mature B cells. Antibody genes were also found to be modified in such cells in germinal centers by recombination of the variable (V), diversity (D), and joining (J) segments. The ability to alter immunoglobulin expression by V(D)J recombination in the selective environment of the germinal center may be an additional mechanism for inactivation or diversification of immune responses.
Synthesis of Nanoparticles and Nanotubes with Well-Separated Layers of Boron Nitride and Carbon
Authors: Suenaga K. , Colliex C. , Demoncy N. , Loiseau A. , Pascard H. , Willaime F.
Published: July 2002

Polyhedral and tubular graphitic nanoparticles made of carbon layers and boron nitride (BN) layers have been synthesized. These particles were observed in the soot collected on the anode deposit formed by arcing a hafnium diboride rod with graphite in a nitrogen atmosphere. Elemental profiles with subnanometer-scale resolution revealed a strong phase separation between BN layers and carbon layers along the radial direction. Most of these tubes have a sandwich structure with carbon layers both in the center and at the periphery, separated by a few BN layers. This structure provides insight into the atomistic mechanism of nanotube growth in the boron-carbon-nitrogen ternary system and may lead to the creation of nanostructured electronic devices relying on the controlled production of heteroatomic nanotubes.
Conversion of Bcl-2 to a Bax-like Death Effector by Caspases
Authors: Cheng Emily H.-Y. , Kirsch David G. , Clem Rollie J. , Ravi Rajani , Kastan Michael B. , Bedi Atul , Ueno Kazuyoshi , Hardwick J. Marie
Published: July 2002

Caspases are a family of cysteine proteases implicated in the biochemical and morphological changes that occur during apoptosis (programmed cell death). The loop domain of Bcl-2 is cleaved at Asp
34
by caspase-3 (CPP32) in vitro, in cells overexpressing caspase-3, and after induction of apoptosis by Fas ligation and interleukin-3 withdrawal. The carboxyl-terminal Bcl-2 cleavage product triggered cell death and accelerated Sindbis virus–induced apoptosis, which was dependent on the BH3 homology and transmembrane domains of Bcl-2. Inhibitor studies indicated that cleavage of Bcl-2 may further activate downstream caspases and contribute to amplification of the caspase cascade. Cleavage-resistant mutants of Bcl-2 had increased protection from interleukin-3 withdrawal and Sindbis virus–induced apoptosis. Thus, cleavage of Bcl-2 by caspases may ensure the inevitability of cell death.
Change in Chemoattractant Responsiveness of Developing Axons at an Intermediate Target
Authors: Shirasaki Ryuichi , Katsumata Ryuta , Murakami Fujio
Published: July 2002

Developing axons reach their final targets as a result of a series of axonal projections to successive intermediate targets. Long-range chemoattraction by intermediate targets plays a key role in this process. Growing axons, however, do not stall at the intermediate targets, where the chemoattractant concentration is expected to be maximal. Commissural axons in the metencephalon, initially attracted by a chemoattractant released from the floor plate, were shown to lose responsiveness to the chemoattractant when they crossed the floor plate in vitro. Such changes in axon responsiveness to chemoattractants may enable developing axons to continue to navigate toward their final destinations.
Role of Ceruloplasmin in Cellular Iron Uptake
Authors: Mukhopadhyay Chinmay K. , Attieh Zouhair K. , Fox Paul L.
Published: July 2002

Individuals with hereditary ceruloplasmin (Cp) deficiency have profound iron accumulation in most tissues, which suggests that Cp is important for normal release of cellular iron. Here, in contrast to expectations, Cp was shown to increase iron uptake by HepG2 cells, increasing the apparent affinity for the substrate by three times. Consistent with its role in iron uptake, Cp synthesis was regulated by iron supply and was increased four- to fivefold after iron depletion. Unlike other iron controllers that are posttranscriptionally regulated, Cp synthesis was transcriptionally regulated. Thus, iron-deficient cells could increase Cp synthesis to maintain intracellular iron homeostasis, so that defects would lead to global accumulation of iron in tissues.
Frictional Melting During the Rupture of the 1994 Bolivian Earthquake
Authors: Kanamori Hiroo , Anderson Don L. , Heaton Thomas H.
Published: July 2002

The source parameters of the 1994 Bolivian earthquake (magnitude
M
w
= 8.3) suggest that the maximum seismic efficiency η was 0.036 and the minimum frictional stress was 550 bars. Thus, the source process was dissipative, which is consistent with the observed slow rupture speed, only 20% of the local
S
-wave velocity. The amount of nonradiated energy produced during the Bolivian rupture was comparable to, or larger than, the thermal energy of the 1980 Mount St. Helens eruption and was sufficient to have melted a layer as thick as 31 centimeters. Once rupture was initiated, melting could occur, which reduces friction and promotes fault slip.
Pleiotropy and the Preservation of Perfection
Authors: Waxman David , Peck Joel R.
Published: July 2002

A mathematical model is presented in which a single mutation can affect multiple phenotypic characters, each of which is subject to stabilizing selection. A wide range of mutations is allowed, including ones that produce extremely small phenotypic changes. The analysis shows that, when three or more characters are affected by each mutation, a single optimal genetic sequence may become common. This result provides a hypothesis to explain the low levels of variation and low rates of substitution that are observed at some loci.
Geographic Variation in the Molluscan Recovery from the End-Cretaceous Extinction
Authors: Jablonski David
Published: July 2002

Biotic recovery patterns after the end-Cretaceous mass extinction differ among the molluscan faunas of the North American Gulf Coast, northern Europe, northern Africa, and Pakistan and northern India. In contrast to the Gulf Coast, the other three regions lack a rapid expansion and decline of “bloom taxa” and have lower proportions of invaders early in the recovery phase. The anomalous Gulf Coast patterns, distinct from extratropical Europe and the tropical regions, provide evidence for the biogeographic and macroevolutionary complexity of biotic recoveries and may have implications for present-day biotas.
Contingency and Determinism in Replicated Adaptive Radiations of Island Lizards
Authors: Losos Jonathan B. , Jackman Todd R. , Larson Allan , Queiroz Kevin de , Rodrı́guez-Schettino Lourdes
Published: July 2002

The vagaries of history lead to the prediction that repeated instances of evolutionary diversification will lead to disparate outcomes even if starting conditions are similar. We tested this proposition by examining the evolutionary radiation of
Anolis
lizards on the four islands of the Greater Antilles. Morphometric analyses indicate that the same set of habitat specialists, termed ecomorphs, occurs on all four islands. Although these similar assemblages could result from a single evolutionary origin of each ecomorph, followed by dispersal or vicariance, phylogenetic analysis indicates that the ecomorphs originated independently on each island. Thus, adaptive radiation in similar environments can overcome historical contingencies to produce strikingly similar evolutionary outcomes.
Requirement of Ras-GTP-Raf Complexes for Activation of Raf-1 by Protein Kinase C
Authors: Marais Richard , Light Yvonne , Mason Clive , Paterson Hugh , Olson Michael F. , Marshall Christopher J.
Published: July 2002

Receptor tyrosine kinase–mediated activation of the Raf-1 protein kinase is coupled to the small guanosine triphosphate (GTP)–binding protein Ras. By contrast, protein kinase C (PKC)–mediated activation of Raf-1 is thought to be Ras independent. Nevertheless, stimulation of PKC in COS cells led to activation of Ras and formation of Ras–Raf-1 complexes containing active Raf-1. Raf-1 mutations that prevent its association with Ras blocked activation of Raf-1 by PKC. However, the activation of Raf-1 by PKC was not blocked by dominant negative Ras, indicating that PKC activates Ras by a mechanism distinct from that initiated by activation of receptor tyrosine kinases.
Flower-Associated Brachycera Flies as Fossil Evidence for Jurassic Angiosperm Origins
Authors: Ren Dong
Published: July 2002

Pollinating insects played a decisive role in the origin and early evolution of the angiosperms. Pollinating orthorrhaphous Brachycera fossils (short-horned flies) collected from Late Jurassic rocks in Liaoning Province of northeast China provide evidence for a pre-Cretaceous origin of angiosperms. Functional morphology and comparison with modern confamilial taxa show that the orthorrhaphous Brachycera were some of the most ancient pollinators. These data thus imply that angiosperms originated during the Late Jurassic and were represented by at least two floral types.
Two-Fraction Model of Initial Sediment Motion in Gravel-Bed Rivers
Authors: Wilcock Peter R.
Published: July 2002

The prediction of sediment transport in gravel-bed rivers is essential to the management of land, water, and ecological resources in mountain regions. Dividing the bed sediment into two populations—sand and gravel—permits realistic and useful predictions of the onset of sediment transport. The critical flow initiating grain motion decreases rapidly with sand content over the transition from a gravel-framework bed to a sand-matrix bed. The two-fraction model provides a simple means of forecasting the movement of excess fine sediment supply. The model also helps to explain the development of the abrupt gravel-sand transition commonly observed in natural rivers.
Maternal Control of Embryogenesis by
MEDEA
, a
Polycomb
Group Gene in
Arabidopsis
Authors: Grossniklaus Ueli , Vielle-Calzada Jean-Philippe , Hoeppner Marilu A. , Gagliano Wendy B.
Published: July 2002

The gametophytic maternal effect mutant
medea
(
mea
) shows aberrant growth regulation during embryogenesis in
Arabidopsis thaliana
. Embryos derived from
mea
eggs grow excessively and die during seed desiccation. Embryo lethality is independent of the paternal contribution and gene dosage. The
mea
phenotype is consistent with the parental conflict theory for the evolution of parent-of-origin–specific effects.
MEA
encodes a SET domain protein similar to
Enhancer of zeste
, a member of the
Polycomb
group. In animals,
Polycomb
group proteins ensure the stable inheritance of expression patterns through cell division and regulate the control of cell proliferation.
Pressure-Induced Amorphization and Negative Thermal Expansion in ZrW
2
O
8
Authors: Perottoni C. A. , Jornada J. A. H. da
Published: July 2002

It has recently been shown that zirconium tungstate (ZrW
2
O
8
) exhibits isotropic negative thermal expansion over its entire temperature range of stability. This rather unusual behavior makes this compound particularly suitable for testing model predictions of a connection between negative thermal expansion and pressure-induced amorphization. High-pressure x-ray diffraction and Raman scattering experiments showed that ZrW
2
O
8
becomes progressively amorphous from 1.5 to 3.5 gigapascals. The amorphous phase was retained after pressure release, but the original crystalline phase returned after annealing at 923 kelvin. The results indicate a general trend between negative thermal expansion and pressure-induced amorphization in highly flexible framework structures.
Aspirin-like Molecules that Covalently Inactivate Cyclooxygenase-2
Authors: Kalgutkar Amit S. , Crews Brenda C. , Rowlinson Scott W. , Garner Carlos , Seibert Karen , Marnett Lawrence J.
Published: July 2002

Many of aspirin's therapeutic effects arise from its acetylation of cyclooxygenase-2 (COX-2), whereas its antithrombotic and ulcerogenic effects result from its acetylation of COX-1. Here, aspirin-like molecules were designed that preferentially acetylate and irreversibly inactivate COX-2. The most potent of these compounds was
o
-(acetoxyphenyl)hept-2-ynyl sulfide (APHS). Relative to aspirin, APHS was 60 times as reactive against COX-2 and 100 times as selective for its inhibition; it also inhibited COX-2 in cultured macrophages and colon cancer cells and in the rat air pouch in vivo. Such compounds may lead to the development of aspirin-like drugs for the treatment or prevention of immunological and proliferative diseases without gastrointestinal or hematologic side effects.
Dynamics of Glasses and Glass-Forming Liquids Studied by Inelastic X-ray Scattering
Authors: Sette Francesco , Krisch Michael H. , Masciovecchio Claudio , Ruocco Giancarlo , Monaco Giulio
Published: July 2002

The development of inelastic x-ray scattering with millielectron volt energy resolution at the European Synchrotron Radiation Facility in Grenoble, France, provides a method for studying high-frequency collective dynamics in disordered systems. This has led to the observation of propagating acoustic phonon-like excitations in glasses and glass-forming liquids down to wavelengths comparable to the interparticle distance. Using the inelastic x-ray scattering results on glycerol as a representative example, it is shown that the microscopic dynamic properties are related to the excess of vibrational states in glasses and to the consequences at the microscopic level of the liquid-glass transition. Moreover, they allow derivation of the infinite frequency sound velocity, a quantity related to the structural relaxation times and to the change of ergodicity at the liquid-glass transition.
Concerted Evolution in an Egg Receptor for a Rapidly Evolving Abalone Sperm Protein
Authors: Swanson Willie J. , Vacquier Victor D.
Published: July 2002

Gamete interactions during fertilization exhibit species specificity. In abalone, the sperm protein lysin species-specifically creates a hole in the egg envelope. Lysin evolves rapidly by positive Darwinian selection. Evolution of the egg receptor for lysin provides the selective pressure for lysin's divergence. The egg receptor for lysin is a tandemly repeated sequence that evolves by concerted evolution. Concerted evolution in the egg receptor could explain the rapid, adaptive evolution in sperm lysin and may provide an underlying molecular mechanism that gives rise to species-specific fertilization.
Evidence Against a Significant Younger Dryas Cooling Event in New Zealand
Authors: Singer Christiane , Shulmeister James , McLea Bill
Published: July 2002

Pollen records of deglacial sequences from northwest Nelson, New Zealand, demonstrate that there was no significant temperature decline associated with the Younger Dryas in New Zealand. Records of glacial advances at this time were either the product of increased snow accumulation under enhanced precipitation regimes or random variation rather than the result of a regional thermal decline. This finding supports those models of Younger Dryas initiation that require neither enhanced westerly circulation nor significant thermal decline in the Southern Hemisphere.
Role of IQGAP1, a Target of the Small GTPases Cdc42 and Rac1, in Regulation of E-Cadherin- Mediated Cell-Cell Adhesion
Authors: Kuroda Shinya , Fukata Masaki , Nakagawa Masato , Fujii Katsuhiko , Nakamura Tomoko , Ookubo Tadashi , Izawa Ichiro , Nagase Takahiro , Nomura Nobuo , Tani Hideki , Shoji Ikuo , Matsuura Yoshiharu , Yonehara Shin , Kaibuchi Kozo
Published: July 2002

The small guanosine triphosphatases (GTPases) Cdc42 and Rac1 regulate E-cadherin–mediated cell-cell adhesion. IQGAP1, a target of Cdc42 and Rac1, was localized with E-cadherin and β-catenin at sites of cell-cell contact in mouse L fibroblasts expressing E-cadherin (EL cells), and interacted with E-cadherin and β-catenin both in vivo and in vitro. IQGAP1 induced the dissociation of α-catenin from a cadherin-catenin complex in vitro and in vivo. Overexpression of IQGAP1 in EL cells, but not in L cells expressing an E-cadherin–α-catenin chimeric protein, resulted in a decrease in E-cadherin–mediated cell-cell adhesive activity. Thus, IQGAP1, acting downstream of Cdc42 and Rac1, appears to regulate cell-cell adhesion through the cadherin-catenin pathway.
Reversal of Phencyclidine Effects by a Group II Metabotropic Glutamate Receptor Agonist in Rats
Authors: Moghaddam Bita , Adams Barbara W.
Published: July 2002

Glutamatergic abnormalities have been associated with several psychiatric disorders, including schizophrenia and addiction. Group II metabotropic glutamate receptors were targeted to normalize glutamatergic disruptions associated with an animal model of schizophrenia, the phencyclidine model. An agonist of this group of receptors, at a dose that was without effects on spontaneous activity and corticolimbic dopamine neurotransmission, attenuated the disruptive effects of phencyclidine on working memory, stereotypy, locomotion, and cortical glutamate efflux. This behavioral reversal occurred in spite of sustained dopamine hyperactivity. Thus, targeting this group of receptors may present a nondopaminergic therapeutic strategy for treatment of psychiatric disorders.
Enhanced Positive Cloud-to-Ground Lightning in Thunderstorms Ingesting Smoke from Fires
Authors: Lyons Walter A. , Nelson Thomas E. , Williams Earle R. , Cramer John A. , Turner Tommy R.
Published: July 2002

Smoke from forest fires in southern Mexico was advected into the U.S. southern plains from April to June 1998. Cloud-to-ground lightning (CG) flash data from the National Lightning Detection Network matched against satellite-mapped aerosol plumes imply that thunderstorms forming in smoke-contaminated air masses generated large amounts of lightning with positive polarity (+CGs). During 2 months, nearly half a million flashes in the southern plains exhibited +CG percentages that were triple the climatological norm. The peak currents in these +CGs were double the expected value. These thunderstorms also produced abnormally high numbers of mesospheric optical sprites.
Early Central Andean Metalworking from Mina Perdida, Peru
Authors: Burger Richard L. , Gordon Robert B.
Published: July 2002

Copper and gold artifacts in contexts dated to ∼3120 to 3020 carbon-14 years before the present (∼1410 to 1090 calendar years B.C.) recovered in excavations at Mina Perdida, Lurı́n Valley, Peru, show that artisans hammered native metals into thin foils, in some cases with intermediate anneals. They gilded copper artifacts by attaching gold foil. The artifacts show that fundamental elements of the Andean metallurgical tradition were developed before the Chavı́n horizon, and that on the Peruvian coast the working of native copper preceded the production of smelted copper objects.
Viscoelastic Flow in the Lower Crust after the 1992 Landers, California, Earthquake
Authors: Deng Jishu , Gurnis Michael , Kanamori Hiroo , Hauksson Egill
Published: July 2002

Space geodesy showed that broad-scale postseismic deformation occurred after the 1992 Landers earthquake. Three-dimensional modeling shows that afterslip can only explain one horizontal component of the postseismic deformation, whereas viscoelastic flow can explain the horizontal and near-vertical displacements. The viscosity of a weak, about 10-km-thick layer, in the lower crust beneath the rupture zone that controls the rebound is about 10
18
pascal seconds. The viscoelastic behavior of the lower crust may help to explain the extensional structures observed in the Basin and Range province and it may be used for the analysis of earthquake hazard.
Role of Heteromer Formation in GABA
B
Receptor Function
Authors: Kuner Rohini , Köhr Georg , Grünewald Sylvia , Eisenhardt Gisela , Bach Alfred , Kornau Hans-Christian
Published: July 2002

Recently, GBR1, a seven-transmembrane domain protein with high affinity for γ-aminobutyric acid (GABA)
B
receptor antagonists, was identified. Here, a GBR1-related protein, GBR2, was shown to be coexpressed with GBR1 in many brain regions and to interact with it through a short domain in the carboxyl-terminal cytoplasmic tail. Heterologously expressed GBR2 mediated inhibition of adenylyl cyclase; however, inwardly rectifying potassium channels were activated by GABA
B
receptor agonists only upon coexpression with GBR1 and GBR2. Thus, the interaction of these receptors appears to be crucial for important physiological effects of GABA and provides a mechanism in receptor signaling pathways that involve a heterotrimeric GTP-binding protein.
Particle-Stabilized Defect Gel in Cholesteric Liquid Crystals
Authors: Zapotocky Martin , Ramos Laurence , Poulin Philippe , Lubensky T. C. , Weitz D. A.
Published: July 2002

Dispersions of colloidal particles in cholesteric liquid crystals form an unusual solid by stabilizing a network of linear defects under tension in the ideal layered structure of the cholesteric. The large length scales of the cholesteric liquid crystals allowed direct observation of the network structure, and its properties were correlated with rheological measurements of elasticity. This system serves as a model for a class of solids formed when particles are mixed with layered materials such as thermotropic and lyotropic smectic liquid crystals and block copolymers.
Self-Assembly of Flat Nanodiscs in Salt-Free Catanionic Surfactant Solutions
Authors: Zemb Th. , Dubois M. , Demé B. , Gulik-Krzywicki Th.
Published: July 2002

Discs of finite size are a very rare form of stable surfactant self-assembly. It is shown that mixing of two oppositely charged single-chain surfactants can produce rigid nanodiscs as well as swollen lamellar liquid crystals with frozen bilayers. The crucial requirement for obtaining nanodisc self-assembly is the use of H
+
and OH
−
as counterions. These counterions then form water and lower the conductivity to 10 microsiemens per centimeter. In the case of cationic component excess, a dilute solution of nanodiscs is in thermodynamic equilibrium with a lamellar phase. The diameter of the cationic nanodiscs is continuously adjustable from a few micrometers to 30 nanometers, with the positive charge located mainly around the edges.
Fluorescence Spectroscopy of Single Biomolecules
Authors: Weiss Shimon
Published: July 2002

Recent advances in single-molecule detection and single-molecule spectroscopy at room temperature by laser-induced fluorescence offer new tools for the study of individual macromolecules under physiological conditions. These tools relay conformational states, conformational dynamics, and activity of single biological molecules to physical observables, unmasked by ensemble averaging. Distributions and time trajectories of these observables can therefore be measured during a reaction without the impossible need to synchronize all the molecules in the ensemble. The progress in applying these tools to biological studies with the use of fluorophores that are site-specifically attached to macromolecules is reviewed.
Inhibition of Myosin Light Chain Kinase by p21-Activated Kinase
Authors: Sanders Luraynne C. , Matsumura Fumio , Bokoch Gary M. , de Lanerolle Primal
Published: July 2002

p21-activated kinases (PAKs) are implicated in the cytoskeletal changes induced by the Rho family of guanosine triphosphatases. Cytoskeletal dynamics are primarily modulated by interactions of actin and myosin II that are regulated by myosin light chain kinase (MLCK)–mediated phosphorylation of the regulatory myosin light chain (MLC). p21-activated kinase 1 (PAK1) phosphorylates MLCK, resulting in decreased MLCK activity. MLCK activity and MLC phosphorylation were decreased, and cell spreading was inhibited in baby hamster kidney–21 and HeLa cells expressing constitutively active PAK1. These data indicate that MLCK is a target for PAKs and that PAKs may regulate cytoskeletal dynamics by decreasing MLCK activity and MLC phosphorylation.
Slow Deformation and Lower Seismic Hazard at the New Madrid Seismic Zone
Authors: Newman Andrew , Stein Seth , Weber John , Engeln Joseph , Mao Ailin , Dixon Timothy
Published: July 2002

Global Positioning System (GPS) measurements across the New Madrid seismic zone (NMSZ) in the central United States show little, if any, motion. These data are consistent with platewide continuous GPS data away from the NMSZ, which show no motion within uncertainties. Both these data and the frequency-magnitude relation for seismicity imply that had the largest shocks in the series of earthquakes that occurred in 1811 and 1812 been magnitude 8, their recurrence interval should well exceed 2500 years, longer than has been assumed. Alternatively, the largest 1811 and 1812 earthquakes and those in the paleoseismic record may have been much smaller than typically assumed. Hence, the hazard posed by great earthquakes in the NMSZ appears to be overestimated.
Electron Solvation in Finite Systems: Femtosecond Dynamics of Iodide·(Water)

n

Anion Clusters
Authors: Lehr L. , Zanni M. T. , Frischkorn C. , Weinkauf R. , Neumark D. M.
Published: July 2002

Electron solvation dynamics in photoexcited anion clusters of I
−
(D
2
O)

n
=4–6

and I
−
(H
2
O)
4–6
were probed by using femtosecond photoelectron spectroscopy (FPES). An ultrafast pump pulse excited the anion to the cluster analog of the charge-transfer-to-solvent state seen for I
−
in aqueous solution. Evolution of this state was monitored by time-resolved photoelectron spectroscopy using an ultrafast probe pulse. The excited
n
= 4 clusters showed simple population decay, but in the
n
= 5 and 6 clusters the solvent molecules rearranged to stabilize and localize the excess electron, showing characteristics associated with electron solvation dynamics in bulk water. Comparison of the FPES of I
−
(D
2
O)

n

with I
−
(H
2
O)

n

indicates more rapid solvation in the H
2
O clusters.
Spectroscopic Determination of the Water Pair Potential
Authors: Fellers R. S. , Leforestier C. , Braly L. B. , Brown M. G. , Saykally R. J.
Published: July 2002

A polarizable water pair potential was determined by fitting a potential form to microwave, terahertz, and mid-infrared (D
2
O)
2
spectra through a rigorous calculation of the water dimer eigenstates. It accurately reproduces most ground state vibration-rotation-tunneling spectra and yields excellent second viral coefficients. The calculated dimer structure and dipole moment are very close to those determined from microwave spectroscopy and high-level ab initio calculations. The dimer binding energy and acceptor switching and donor-acceptor interchange tunneling barriers are in excellent agreement with recent ab initio theory, as are cyclic water trimer and tetramer structures and binding energies.
Design and Self-Assembly of Open, Regular, 3D Mesostructures
Authors: Breen Tricia L. , Tien Joe , J. Scott R. , Oliver  , Hadzic Tanja , Whitesides George M.
Published: July 2002

Self-assembly provides the basis for a procedure used to organize millimeter-scale objects into regular, three-dimensional arrays (“crystals”) with open structures. The individual components are designed and fabricated of polyurethane by molding; selected faces are coated with a thin film of liquid, metallic alloy. Under mild agitation in warm, aqueous potassium bromide solution, capillary forces between the films of alloy cause self-assembly. The structures of the resulting, self-assembled arrays are determined by structural features of the component parts: the three-dimensional shape of the components, the pattern of alloy on their surfaces, and the shape of the alloy-coated surfaces. Self-assembly of appropriately designed chiral pieces generates helices.
Spatiotemporal Dynamics of Inositol 1,4,5-Trisphosphate That Underlies Complex Ca
2+
Mobilization Patterns
Authors: Hirose Kenzo , Kadowaki Shiro , Tanabe Mao , Takeshima Hiroshi , Iino Masamitsu
Published: July 2002

Inositol 1,4,5-trisphosphate (IP
3
) is a second messenger that elicits complex spatiotemporal patterns of calcium ion (Ca
2+
) mobilization and has essential roles in the regulation of many cellular functions. In Madin-Darby canine kidney epithelial cells, green fluorescent protein–tagged pleckstrin homology domain translocated from the plasma membrane to the cytoplasm in response to increased concentration of IP
3
. The detection of translocation enabled monitoring of IP
3
concentration changes within single cells and revealed spatiotemporal dynamics in the concentration of IP
3
synchronous with Ca
2+
oscillations and intracellular and intercellular IP
3
waves that accompanied Ca
2+
waves. Such changes in IP
3
concentration may be fundamental to Ca
2+
signaling.
Interactions of Prefrontal Cortex in Relation to Awareness in Sensory Learning
Authors: McIntosh Anthony Randal , Rajah M. Natasha , Lobaugh Nancy J.
Published: July 2002

In an associative learning paradigm, human subjects could be divided based on whether they were aware that one tone predicted a visual event and another did not. Only aware subjects acquired a differential behavioral response to the tones. Regional cerebral blood flow in left prefrontal cortex showed learning-related changes only in aware subjects. Left prefrontal cortex also showed changes in functional connectivity with contralateral prefrontal cortex, sensory association cortices, and cerebellum. Several of the interacting areas correlated with aware subjects' behavior. These results suggest cerebral processes underlying awareness are mediated through interactions of large-scale neurocognitive systems.
The Fourth Dimension of Life: Fractal Geometry and Allometric Scaling of Organisms
Authors: West Geoffrey B. , Brown James H. , Enquist Brian J.
Published: July 2002

Fractal-like networks effectively endow life with an additional fourth spatial dimension. This is the origin of quarter-power scaling that is so pervasive in biology. Organisms have evolved hierarchical branching networks that terminate in size-invariant units, such as capillaries, leaves, mitochondria, and oxidase molecules. Natural selection has tended to maximize both metabolic capacity, by maximizing the scaling of exchange surface areas, and internal efficiency, by minimizing the scaling of transport distances and times. These design principles are independent of detailed dynamics and explicit models and should apply to virtually all organisms.