bluuebunny/crossref_metadata_2025 huggingface dataset:
Blood Flow Regulation by
S
-Nitrosohemoglobin in the Physiological Oxygen Gradient
Authors: Stamler Jonathan S. , Jia Li , Eu Jerry P. , McMahon Timothy J. , Demchenko Ivan T. , Bonaventura Joseph , Gernert Kim , Piantadosi Claude A.
Published: July 2002

The binding of oxygen to heme irons in hemoglobin promotes the binding of nitric oxide (NO) to cysteineβ93, forming
S
-nitrosohemoglobin. Deoxygenation is accompanied by an allosteric transition in
S
-nitrosohemoglobin [from the R (oxygenated) to the T (deoxygenated) structure] that releases the NO group.
S
-nitrosohemoglobin contracts blood vessels and decreases cerebral perfusion in the R structure and relaxes vessels to improve blood flow in the T structure. By thus sensing the physiological oxygen gradient in tissues, hemoglobin exploits conformation-associated changes in the position of cysteineβ93 SNO to bring local blood flow into line with oxygen requirements.
Pericyte Loss and Microaneurysm Formation in PDGF-B-Deficient Mice
Authors: Lindahl Per , Johansson Bengt R. , Levéen Per , Betsholtz Christer
Published: July 2002

Platelet-derived growth factor (PDGF)–B–deficient mouse embryos were found to lack microvascular pericytes, which normally form part of the capillary wall, and they developed numerous capillary microaneurysms that ruptured at late gestation. Endothelial cells of the sprouting capillaries in the mutant mice appeared to be unable to attract PDGF-Rβ–positive pericyte progenitor cells. Pericytes may contribute to the mechanical stability of the capillary wall. Comparisons made between PDGF null mouse phenotypes suggest a general role for PDGFs in the development of myofibroblasts.
Evidence for a Large-Scale Reorganization of Early Cambrian Continental Masses by Inertial Interchange True Polar Wander
Authors: Kirschvink Joseph L. , Ripperdan Robert L. , Evans David A.
Published: July 2002

Analysis of Vendian to Cambrian paleomagnetic data shows anomalously fast rotations and latitudinal drift for all of the major continents. These motions are consistent with an Early to Middle Cambrian inertial interchange true polar wander event, during which Earth's lithosphere and mantle rotated about 90 degrees in response to an unstable distribution of the planet's moment of inertia. The proposed event produces a longitudinally constrained Cambrian paleogeography and accounts for rapid rates of continental motion during that time.
Mitochondrial and Chloroplast Phage-Type RNA Polymerases in
Arabidopsis
Authors: Hedtke Boris , Börner Thomas , Weihe Andreas
Published: July 2002

In addition to the RNA polymerases (RNAPs) transcribing the nuclear genes, eukaryotic cells also require RNAPs to transcribe the genes of the mitochondrial genome and, in plants, of the chloroplast genome. The plant
Arabidopsis thaliana
was found to contain two nuclear genes similar to genes encoding the mitochondrial RNAP from yeast and RNAPs of bacteriophages T7, T3, and SP6. The putative transit peptides of the two polymerases were capable of targeting fusion proteins to mitochondria and chloroplasts, respectively, in vitro. The results indicate that the mitochondrial RNAP in plants is a bacteriophage-type enzyme. A gene duplication event may have generated the second RNAP, which along with the plastid-encoded eubacteria-like RNAP could transcribe the chloroplast genome.
Altered Neural Cell Fates and Medulloblastoma in Mouse
patched
Mutants
Authors: Goodrich Lisa V. , Milenković Ljiljana , Higgins Kay M. , Scott Matthew P.
Published: July 2002

The
PATCHED
(
PTC
) gene encodes a Sonic hedgehog (Shh) receptor and a tumor suppressor protein that is defective in basal cell nevus syndrome (BCNS). Functions of
PTC
were investigated by inactivating the mouse gene. Mice homozygous for the
ptc
mutation died during embryogenesis and were found to have open and overgrown neural tubes. Two Shh target genes,
ptc
itself and
Gli
, were derepressed in the ectoderm and mesoderm but not in the endoderm. Shh targets that are, under normal conditions, transcribed ventrally were aberrantly expressed in dorsal and lateral neural tube cells. Thus Ptc appears to be essential for repression of genes that are locally activated by Shh. Mice heterozygous for the
ptc
mutation were larger than normal, and a subset of them developed hindlimb defects or cerebellar medulloblastomas, abnormalities also seen in BCNS patients.
Structure Determination of Mg
5
Si
6
Particles in Al by Dynamic Electron Diffraction Studies
Authors: Zandbergen H. W. , Andersen S. J. , Jansen J.
Published: July 2002

Precipitation hardening, in which small particles inhibit the movement of dislocations to strengthen a metal, has long been used to improve mechanical strength, especially of aluminum alloys. The small size of precipitates and the many possible variants of the orientation relation have made their structural determination difficult. Small precipitates in commercial aluminum-magnesium-silicon alloys play a crucial role in increasing the mechanical strength of these alloys. The composition and structure of the β” phase in an aluminum-magnesium-silicon alloy, which occur as precipitates (typically 4 nanometers by 4 nanometers by 50 nanometers) and are associated with a particularly strong increase in mechanical strength, were determined. Element analysis indicates that the composition is Mg
5
Si
6
. A rough structure model was obtained from exit waves reconstructed from high-resolution electron microscopy images. The structure was refined with electron nanodiffraction data (overall
R
value of 3.1 percent) with the use of a recently developed least squares refinement procedure in which dynamic diffraction is fully taken into account.
Induced α Helix in the VP16 Activation Domain upon Binding to a Human TAF
Authors: Uesugi Motonari , Nyanguile Origène , Lu Hua , Levine Arnold J. , Verdine Gregory L.
Published: July 2002

Activation domains are functional modules that enable sequence-specific DNA binding proteins to stimulate transcription. The structural basis for the function of activation domains is poorly understood. A combination of nuclear magnetic resonance (NMR) and biochemical experiments revealed that the minimal acidic activation domain of the herpes simplex virus VP16 protein undergoes an induced transition from random coil to α helix upon binding to its target protein, hTAF
II
31 (a human TFIID TATA box
–
binding protein-associated factor). Identification of the two hydrophobic residues that make nonpolar contacts suggests a general recognition motif of acidic activation domains for hTAF
II
31.
The Response of Jupiter's Magnetosphere to an Outburst on Io
Authors: Brown Michael E. , Bouchez Antonin H.
Published: July 2002

A 6-month-long monitoring campaign of the Io plasma torus and neutral cloud was conducted to determine the characteristics of their interaction. During the observations, a large outburst of material from Io—inferred to be caused by the eruption of a volcanic plume on Io—caused a transient increase in the neutral cloud and plasma torus masses. The response of the plasma torus to this outburst shows that the interaction between Io and Jupiter's magnetosphere is stabilized by a feedback mechanism in which increases in the plasma torus mass cause a nonlinear increase in loss from the plasma torus, limiting plasma buildup.
Genetics of Aging
Authors: Finch Caleb E. , Tanzi Rudolph E.
Published: July 2002

The role of genetics in determining life-span is complex and paradoxical. Although the heritability of life-span is relatively minor, some genetic variants significantly modify senescence of mammals and invertebrates, with both positive and negative impacts on age-related disorders and life-spans. In certain examples, the gene variants alter metabolic pathways, which could thereby mediate interactions with nutritional and other environmental factors that influence life-span. Given the relatively minor effect and variable penetrance of genetic risk factors that appear to affect survival and health at advanced ages, life-style and other environmental influences may profoundly modify outcomes of aging.
Population Diversity: Its Extent and Extinction
Authors: Hughes Jennifer B. , Daily Gretchen C. , Ehrlich Paul R.
Published: July 2002

Genetically distinct populations are an important component of biodiversity. This work estimates the number of populations per area of a sample of species from literature on population differentiation and the average range area of a species from a sample of distribution maps. This yields an estimate of about 220 populations per species, or 1.1 to 6.6 billion populations globally. Assuming that population extinction is a linear function of habitat loss, approximately 1800 populations per hour (16 million annually) are being destroyed in tropical forests alone.
Metal Ion Chaperone Function of the Soluble Cu(I) Receptor Atx1
Authors: Pufahl R. A. , Singer C. P. , Peariso K. L. , Lin S.-J. , Schmidt P. J. , Fahrni C. J. , Culotta V. Cizewski , Penner-Hahn J. E. , O'Halloran T. V.
Published: July 2002

Reactive and potentially toxic cofactors such as copper ions are imported into eukaryotic cells and incorporated into target proteins by unknown mechanisms. Atx1, a prototypical copper chaperone protein from yeast, has now been shown to act as a soluble cytoplasmic copper(I) receptor that can adopt either a two- or three-coordinate metal center in the active site. Atx1 also associated directly with the Atx1-like cytosolic domains of Ccc2, a vesicular protein defined in genetic studies as a member of the copper-trafficking pathway. The unusual structure and dynamics of Atx1 suggest a copper exchange function for this protein and related domains in the Menkes and Wilson disease proteins.
Abiotic Selenium Redox Transformations in the Presence of Fe(II,III) Oxides
Authors: Myneni S. C. B. , Tokunaga T. K. , Brown G. E.
Published: July 2002

Many suboxic sediments and soils contain an Fe(II,III) oxide called green rust. Spectroscopic evidence showed that selenium reduces from an oxidation state of +VI to 0 in the presence of green rust at rates comparable with those found in sediments. Selenium speciation was different in solid and aqueous phases. These redox reactions represent an abiotic pathway for selenium cycling in natural environments, which has previously been considered to be mediated principally by microorganisms. Similar green rust–mediated abiotic redox reactions are likely to be involved in the mobility of several other trace elements and contaminants in the environment.
Site of Einkorn Wheat Domestication Identified by DNA Fingerprinting
Authors: Heun Manfred , Schäfer-Pregl Ralf , Klawan Dieter , Castagna Renato , Accerbi Monica , Borghi Basilio , Salamini Francesco
Published: July 2002

The emergence of agriculture in the Near East also involved the domestication of einkorn wheat. Phylogenetic analysis that was based on the allelic frequency at 288 amplified fragment length polymorphism molecular marker loci indicates that a wild group of
Triticum monococcum boeoticum
lines from the Karacadağ mountains (southeast Turkey) is the likely progenitor of cultivated einkorn varieties. Evidence from archeological excavations of early agricultural settlements nearby supports the conclusion that domestication of einkorn wheat began near the Karacadağmountains.
Impact of Lower Atmospheric Carbon Dioxide on Tropical Mountain Ecosystems
Authors: Street-Perrott F. Alayne , Huang Yongsong , Perrott R. Alan , Eglinton Geoffrey , Barker Philip , Khelifa Leila Ben , Harkness Douglas D. , Olago Daniel O.
Published: July 2002

Carbon-isotope values of bulk organic matter from high-altitude lakes on Mount Kenya and Mount Elgon, East Africa, were 10 to 14 per mil higher during glacial times than they are today. Compound-specific isotope analyses of leaf waxes and algal biomarkers show that organisms possessing CO
2
-concentrating mechanisms, including C
4
grasses and freshwater algae, were primarily responsible for this large increase. Carbon limitation due to lower ambient CO
2
partial pressures had a significant impact on the distribution of forest on the tropical mountains, in addition to climate. Hence, tree line elevation should not be used to infer palaeotemperatures.
Thermohaline Circulation, the Achilles Heel of Our Climate System: Will Man-Made CO
2
Upset the Current Balance?
Authors: Broecker Wallace S.
Published: July 2002

During the last glacial period, Earth's climate underwent frequent large and abrupt global changes. This behavior appears to reflect the ability of the ocean's thermohaline circulation to assume more than one mode of operation. The record in ancient sedimentary rocks suggests that similar abrupt changes plagued the Earth at other times. The trigger mechanism for these reorganizations may have been the antiphasing of polar insolation associated with orbital cycles. Were the ongoing increase in atmospheric CO
2
levels to trigger another such reorganization, it would be bad news for a world striving to feed 11 to 16 billion people.
Quantum-Confined Stark Effect in Single CdSe Nanocrystallite Quantum Dots
Authors: Empedocles S. A. , Bawendi M. G.
Published: July 2002

The quantum-confined Stark effect in single cadmium selenide (CdSe) nanocrystallite quantum dots was studied. The electric field dependence of the single-dot spectrum is characterized by a highly polarizable excited state (∼10
5
cubic angstroms, compared to typical molecular values of order 10 to 100 cubic angstroms), in the presence of randomly oriented local electric fields that change over time. These local fields result in spontaneous spectral diffusion and contribute to ensemble inhomogeneous broadening. Stark shifts of the lowest excited state more than two orders of magnitude larger than the linewidth were observed, suggesting the potential use of these dots in electro-optic modulation devices.
Memory Suppressor Genes: Inhibitory Constraints on the Storage of Long-Term Memory
Authors: Abel Ted , Martin Kelsey C. , Bartsch Dusan , Kandel Eric R.
Published: July 2002

Synaptic plasticity, the ability of neurons to alter the strength of their synaptic connections with activity and experience, is thought to play a critical role in memory storage. Molecular studies of gene expression during long-lasting synaptic plasticity related to memory storage initially focused on the identification of positive regulators. More recent work has revealed that the establishment of long-lasting synaptic plasticity and long-term memory also requires the removal of inhibitory constraints. By analogy to tumor supressor genes, which restrain cell proliferation, we propose that these inhibitory constraints on memory storage, which restrain synapse growth, be termed memory suppressor genes.
Natural Ligand of Mouse CD1d1: Cellular Glycosylphosphatidylinositol
Authors: Joyce Sebastian , Woods Amina S. , Yewdell Jonathan W. , Bennink Jack R. , De Silva A. Dharshan , Boesteanu Alina , Balk Steven P. , Cotter Robert J. , Brutkiewicz Randy R.
Published: July 2002

Mouse CD1d1, a member of the CD1 family of evolutionarily conserved major histocompatibility antigen–like molecules, controls the differentiation and function of a T lymphocyte subset, NK1
+
natural T cells, proposed to regulate immune responses. The CD1d1 crystal structure revealed a large hydrophobic binding site occupied by a ligand of unknown chemical nature. Mass spectrometry and metabolic radiolabeling were used to identify cellular glycosylphosphatidylinositol as a major natural ligand of CD1d1. CD1d1 bound glycosylphosphatidylinositol through its phosphatidylinositol aspect with high affinity. Glycosylphosphatidylinositol or another glycolipid could be a candidate natural ligand for CD1d1-restricted T cells.
Magnetic Field and Plasma Observations at Mars: Initial Results of the Mars Global Surveyor Mission
Authors: Acuña M. H. , Connerney J. E. P. , Wasilewski P. , Lin R. P. , Anderson K. A. , Carlson C. W. , McFadden J. , Curtis D. W. , Mitchell D. , Reme H. , Mazelle C. , Sauvaud J. A. , d'Uston C. , Cros A. , Medale J. L. , Bauer S. J. , Cloutier P. , Mayhew M. , Winterhalter D. , Ness N. F.
Published: July 2002

The magnetometer and electron reflectometer investigation (MAG/ER) on the Mars Global Surveyor spacecraft has obtained magnetic field and plasma observations throughout the near-Mars environment, from beyond the influence of Mars to just above the surface (at an altitude of ∼100 kilometers). The solar wind interaction with Mars is in many ways similar to that at Venus and at an active comet, that is, primarily an ionospheric-atmospheric interaction. No significant planetary magnetic field of global scale has been detected to date (<2 × 10
21
Gauss–cubic centimeter), but here the discovery of multiple magnetic anomalies of small spatial scale in the crust of Mars is reported.
Cortical Map Reorganization Enabled by Nucleus Basalis Activity
Authors: Kilgard Michael P. , Merzenich Michael M.
Published: July 2002

Little is known about the mechanisms that allow the cortex to selectively improve the neural representations of behaviorally important stimuli while ignoring irrelevant stimuli. Diffuse neuromodulatory systems may facilitate cortical plasticity by acting as teachers to mark important stimuli. This study demonstrates that episodic electrical stimulation of the nucleus basalis, paired with an auditory stimulus, results in a massive progressive reorganization of the primary auditory cortex in the adult rat. Receptive field sizes can be narrowed, broadened, or left unaltered depending on specific parameters of the acoustic stimulus paired with nucleus basalis activation. This differential plasticity parallels the receptive field remodeling that results from different types of behavioral training. This result suggests that input characteristics may be able to drive appropriate alterations of receptive fields independently of explicit knowledge of the task. These findings also suggest that the basal forebrain plays an active instructional role in representational plasticity.
Integration of Environmental, Agronomic, and Economic Aspects of Fertilizer Management
Authors: Matson Pamela A. , Naylor Rosamond , Ortiz-Monasterio Ivan
Published: July 2002

Nitrogen fertilization is a substantial source of nitrogen-containing trace gases that have both regional and global consequences. In the intensive wheat systems of Mexico, typical fertilization practices lead to extremely high fluxes of nitrous oxide (N
2
O) and nitric oxide (NO). In experiments, lower rates of nitrogen fertilizer, applied later in the crop cycle, reduced the loss of nitrogen without affecting yield and grain quality. Economic analyses projected this alternative practice to save 12 to 17 percent of after-tax profits. A knowledge-intensive approach to fertilizer management can substitute for higher levels of inputs, saving farmers money and reducing environmental costs.
Delayed Fracture of an Inhomogeneous Soft Solid
Authors: Bonn Daniel , Kellay Hamid , Prochnow Michaël , Ben-Djemiaa Karim , Meunier Jacques
Published: July 2002

The spontaneous fracture of polymer gels was studied. Contrary to crystalline solids, where fracture usually happens instantaneously at a well-defined breaking strength, the fracture of a polymer gel can occur with a delay. When a constant force was applied, the cracks nucleated and started to propagate after a delay that can be as long as 15 minutes, depending on the force. This phenomenon can be understood by calculating the activation energy for crack nucleation in arbitrary dimension and accounting for the inhomogeneity of the gel network in terms of its fractal dimension.
Osmium Isotopic Evidence for Ancient Subcontinental Lithospheric Mantle Beneath the Kerguelen Islands, Southern Indian Ocean
Authors: Hassler Deborah R. , Shimizu Nobumichi
Published: July 2002

Upper mantle xenoliths found in ocean island basalts are an important window through which the oceanic mantle lithosphere may be viewed directly. Osmium isotopic data on peridotite xenoliths from the Kerguelen Islands, an archipelago that is located on the northern Kerguelen Plateau in the southern Indian Ocean, demonstrate that pieces of mantle of diverse provenance are present beneath the Islands. In particular, peridotites with unradiogenic osmium and ancient rhenium-depletion ages (to 1.36 × 10
9
years old) may be pieces of the Gondwanaland subcontinental lithosphere that were incorporated into the Indian Ocean lithosphere as a result of the rifting process.
Actin Mutations in Dilated Cardiomyopathy, a Heritable Form of Heart Failure
Authors: Olson Timothy M. , Michels Virginia V. , Thibodeau Stephen N. , Tai Yin-Shan , Keating Mark T.
Published: July 2002

To test the hypothesis that actin dysfunction leads to heart failure, patients with hereditary idiopathic dilated cardiomyopathy (IDC) were examined for mutations in the cardiac actin gene (
ACTC
). Missense mutations in
ACTC
that cosegregate with IDC were identified in two unrelated families. Both mutations affect universally conserved amino acids in domains of actin that attach to Z bands and intercalated discs. Coupled with previous data showing that dystrophin mutations also cause dilated cardiomyopathy, these results raise the possibility that defective transmission of force in cardiac myocytes is a mechanism underlying heart failure.
Mantle Seismic Structure Beneath the MELT Region of the East Pacific Rise from
P
and
S
Wave Tomography
Authors: Toomey Douglas R. , Wilcock William S. D. , Solomon Sean C. , Hammond William C. , Orcutt John A.
Published: July 2002

Relative travel time delays of teleseismic
P
and
S
waves, recorded during the Mantle Electromagnetic and Tomography (MELT) Experiment, have been inverted tomographically for upper-mantle structure beneath the southern East Pacific Rise. A broad zone of low seismic velocities extends beneath the rise to depths of about 200 kilometers and is centered to the west of the spreading center. The magnitudes of the
P
and
S
wave anomalies require the presence of retained mantle melt; the melt fraction near the rise exceeds the fraction 300 kilometers off axis by as little as 1%. Seismic anisotropy, induced by mantle flow, is evident in the
P
wave delays at near-vertical incidence and is consistent with a half-width of mantle upwelling of about 100 km.
Pleistocene Collapse of the West Antarctic Ice Sheet
Authors: Scherer Reed P. , Aldahan Ala , Tulaczyk Slawek , Possnert Göran , Engelhardt Hermann , Kamb Barclay
Published: July 2002

Some glacial sediment samples recovered from beneath the West Antarctic ice sheet at ice stream B contain Quaternary diatoms and up to 10
8
atoms of beryllium-10 per gram. Other samples contain no Quaternary diatoms and only background levels of beryllium-10 (less than 10
6
atoms per gram). The occurrence of young diatoms and high concentrations of beryllium-10 beneath grounded ice indicates that the Ross Embayment was an open marine environment after a late Pleistocene collapse of the marine ice sheet.
Acquisition and Utilization of Transition Metal Ions by Marine Organisms
Authors: Butler Alison
Published: July 2002

Recent research has revealed that trace metals, particularly transition metals, play important roles in marine productivity. Most of the work has been on iron, which shows a nutrient- depleted profile in the upper ocean. Marine organisms have a variety of means for acquiring iron and other transition metal ions that differ from those of terrestrial organisms.
Cambrian Burgess Shale Animals Replicated in Clay Minerals
Authors: Orr Patrick J. , Briggs Derek E. G. , Kearns Stuart L.
Published: July 2002

Although the evolutionary importance of the Burgess Shale is universally acknowledged, there is disagreement on the mode of preservation of the fossils after burial. Elemental mapping demonstrates that the relative abundance of elements varies between different anatomical features of the specimens. These differences reflect the compositions of the minerals that replicated the decaying organism, which were controlled by contrasts in tissue chemistry. Delicate morphological details are replicated in the elemental maps, showing that authigenic mineralization was fundamental to preserving these fossils, even though some organic remains are also present.
History of Atmospheric Lead Deposition Since 12,370
14
C yr BP from a Peat Bog, Jura Mountains, Switzerland
Authors: Shotyk W. , Weiss D. , Appleby P. G. , Cheburkin A. K. , Frei R. , Gloor M. , Kramers J. D. , Reese S. , Van Der Knaap W. O.
Published: July 2002

A continuous record of atmospheric lead since 12,370 carbon-14 years before the present (
14
C yr BP) is preserved in a Swiss peat bog. Enhanced fluxes caused by climate changes reached their maxima 10,590
14
C yr BP (Younger Dryas) and 8230
14
C yr BP. Soil erosion caused by forest clearing and agricultural tillage increased lead deposition after 5320
14
C yr BP. Increasing lead/scandium and decreasing lead-206/lead-207 beginning 3000
14
C yr BP indicate the beginning of lead pollution from mining and smelting, and anthropogenic sources have dominated lead emissions ever since. The greatest lead flux (15.7 milligrams per square meter per year in A.D. 1979) was 1570 times the natural, background value (0.01 milligram per square meter per year from 8030 to 5320
14
C yr BP).
Aggregation and Motor Neuron Toxicity of an ALS-Linked SOD1 Mutant Independent from Wild-Type SOD1
Authors: Bruijn Lucie I. , Houseweart Megan K. , Kato Shinsuke , Anderson Karen L. , Anderson Scott D. , Ohama Eisaku , Reaume Andrew G. , Scott Rick W. , Cleveland Don W.
Published: July 2002

Analysis of transgenic mice expressing familial amyotrophic lateral sclerosis (ALS)–linked mutations in the enzyme superoxide dismutase (SOD1) have shown that motor neuron death arises from a mutant-mediated toxic property or properties. In testing the disease mechanism, both elimination and elevation of wild-type SOD1 were found to have no effect on mutant-mediated disease, which demonstrates that the use of SOD mimetics is unlikely to be an effective therapy and raises the question of whether toxicity arises from superoxide-mediated oxidative stress. Aggregates containing SOD1 were common to disease caused by different mutants, implying that coaggregation of an unidentified essential component or components or aberrant catalysis by misfolded mutants underlies a portion of mutant-mediated toxicity.
Promotion of Dendritic Growth by CPG15, an Activity-Induced Signaling Molecule
Authors: Nedivi Elly , Wu Gang-Yi , Cline Hollis T.
Published: July 2002

Activity-independent and activity-dependent mechanisms work in concert to regulate neuronal growth, ensuring the formation of accurate synaptic connections. CPG15, a protein regulated by synaptic activity, functions as a cell-surface growth-promoting molecule in vivo. In
Xenopus laevis
, CPG15 enhanced dendritic arbor growth in projection neurons, with no effect on interneurons. CPG15 controlled growth of neighboring neurons through an intercellular signaling mechanism that requires its glycosylphosphatidylinositol link. CPG15 may represent a new class of activity-regulated, membrane-bound, growth-promoting proteins that permit exquisite spatial and temporal control of neuronal structure.
Killer Whale Predation on Sea Otters Linking Oceanic and Nearshore Ecosystems
Authors: Estes J. A. , Tinker M. T. , Williams T. M. , Doak D. F.
Published: July 2002

After nearly a century of recovery from overhunting, sea otter populations are in abrupt decline over large areas of western Alaska. Increased killer whale predation is the likely cause of these declines. Elevated sea urchin density and the consequent deforestation of kelp beds in the nearshore community demonstrate that the otter's keystone role has been reduced or eliminated. This chain of interactions was probably initiated by anthropogenic changes in the offshore oceanic ecosystem.
Induction and Evasion of Host Defenses by Type 1-Piliated Uropathogenic
Escherichia coli
Authors: Mulvey Matthew A. , Lopez-Boado Yolanda S. , Wilson Carole L. , Roth Robyn , Parks William C. , Heuser John , Hultgren Scott J.
Published: July 2002

Virtually all uropathogenic strains of
Escherichia coli
encode filamentous surface adhesive organelles called type 1 pili. High-resolution electron microscopy of infected mouse bladders revealed that type 1 pilus tips interacted directly with the lumenal surface of the bladder, which is embedded with hexagonal arrays of integral membrane glycoproteins known as uroplakins. Attached pili were shortened and facilitated intimate contact of the bacteria with the uroplakin-coated host cells. Bacterial attachment resulted in exfoliation of host bladder epithelial cells as part of an innate host defense system. Exfoliation occurred through a rapid apoptosis-like mechanism involving caspase activation and host DNA fragmentation. Bacteria resisted clearance in the face of host defenses within the bladder by invading into the epithelium.
Zebrafish
hox
Clusters and Vertebrate Genome Evolution
Authors: Amores Angel , Force Allan , Yan Yi-Lin , Joly Lucille , Amemiya Chris , Fritz Andreas , Ho Robert K. , Langeland James , Prince Victoria , Wang Yan-Ling , Westerfield Monte , Ekker Marc , Postlethwait John H.
Published: July 2002

HOX
genes specify cell fate in the anterior-posterior axis of animal embryos. Invertebrate chordates have one
HOX
cluster, but mammals have four, suggesting that cluster duplication facilitated the evolution of vertebrate body plans. This report shows that zebrafish have seven
hox
clusters. Phylogenetic analysis and genetic mapping suggest a chromosome doubling event, probably by whole genome duplication, after the divergence of ray-finned and lobe-finned fishes but before the teleost radiation. Thus, teleosts, the most species-rich group of vertebrates, appear to have more copies of these developmental regulatory genes than do mammals, despite less complexity in the anterior-posterior axis.
Observations of the North Polar Region of Mars from the Mars Orbiter Laser Altimeter
Authors: Zuber Maria T. , Smith David E. , Solomon Sean C. , Abshire James B. , Afzal Robert S. , Aharonson Oded , Fishbaugh Kathryn , Ford Peter G. , Frey Herbert V. , Garvin James B. , Head James W. , Ivanov Anton B. , Johnson Catherine L. , Muhleman Duane O. , Neumann Gregory A. , Pettengill Gordon H. , Phillips Roger J. , Sun Xiaoli , Zwally H. Jay , Banerdt W. Bruce , Duxbury Thomas C.
Published: July 2002

Elevations from the Mars Orbiter Laser Altimeter (MOLA) have been used to construct a precise topographic map of the martian north polar region. The northern ice cap has a maximum elevation of 3 kilometers above its surroundings but lies within a 5-kilometer-deep hemispheric depression that is contiguous with the area into which most outflow channels emptied. Polar cap topography displays evidence of modification by ablation, flow, and wind and is consistent with a primarily H
2
O composition. Correlation of topography with images suggests that the cap was more spatially extensive in the past. The cap volume of 1.2 × 10
6
to 1.7 × 10
6
cubic kilometers is about half that of the Greenland ice cap. Clouds observed over the polar cap are likely composed of CO
2
that condensed out of the atmosphere during northern hemisphere winter. Many clouds exhibit dynamical structure likely caused by the interaction of propagating wave fronts with surface topography.
Assembly and Analysis of Conical Models for the HIV-1 Core
Authors: Ganser Barbie K. , Li Su , Klishko Victor Y. , Finch John T. , Sundquist Wesley I.
Published: July 2002

The genome of the human immunodeficiency virus (HIV) is packaged within an unusual conical core particle located at the center of the infectious virion. The core is composed of a complex of the NC (nucleocapsid) protein and genomic RNA, surrounded by a shell of the CA (capsid) protein. A method was developed for assembling cones in vitro using pure recombinant HIV-1 CA-NC fusion proteins and RNA templates. These synthetic cores are capped at both ends and appear similar in size and morphology to authentic viral cores. It is proposed that both viral and synthetic cores are organized on conical hexagonal lattices, which by Euler's theorem requires quantization of their cone angles. Electron microscopic analyses revealed that the cone angles of synthetic cores were indeed quantized into the five allowed angles. The viral core and most synthetic cones exhibited cone angles of approximately 19 degrees (the narrowest of the allowed angles). These observations suggest that the core of HIV is organized on the principles of a fullerene cone, in analogy to structures recently observed for elemental carbon.
Unresponsiveness to Cannabinoids and Reduced Addictive Effects of Opiates in CB
1
Receptor Knockout Mice
Authors: Ledent Catherine , Valverde Olga , Cossu Gregorio , Petitet François , Aubert Jean-François , Beslot Françoise , Böhme Georg A. , Imperato Assunta , Pedrazzini Thierry , Roques Bernard P. , Vassart Gilbert , Fratta Walter , Parmentier Marc
Published: July 2002

The function of the central cannabinoid receptor (CB
1
) was investigated by invalidating its gene. Mutant mice did not respond to cannabinoid drugs, demonstrating the exclusive role of the CB
1
receptor in mediating analgesia, reinforcement, hypothermia, hypolocomotion, and hypotension. The acute effects of opiates were unaffected, but the reinforcing properties of morphine and the severity of the withdrawal syndrome were strongly reduced. These observations suggest that the CB
1
receptor is involved in the motivational properties of opiates and in the development of physical dependence and extend the concept of an interconnected role of CB
1
and opiate receptors in the brain areas mediating addictive behavior.
Conserved Structures of Mediator and RNA Polymerase II Holoenzyme
Authors: Asturias Francisco J. , Jiang Yi Wei , Myers Lawrence C. , Gustafsson Claes M. , Kornberg Roger D.
Published: July 2002

Single particles of the mediator of transcriptional regulation (Mediator) and of RNA polymerase II holoenzyme were revealed by electron microscopy and image processing. Mediator alone appeared compact, but at high pH or in the presence of RNA polymerase II it displayed an extended conformation. Holoenzyme contained Mediator in a fully extended state, partially enveloping the globular polymerase, with points of apparent contact in the vicinity of the polymerase carboxyl-terminal domain and the DNA-binding channel. A similarity in appearance and conformational behavior of yeast and murine complexes indicates a conservation of Mediator structure among eukaryotes.
Evolution of the Continents and the Atmosphere Inferred from Th-U-Nb Systematics of the Depleted Mantle
Authors: Collerson Kenneth D. , Kamber Balz S.
Published: July 2002

Temporal evolution of depleted mantle thorium-uranium-niobium systematics constrain the amount of continental crust present through Earth's history (through the niobium/thorium ratio) and date formation of a globally oxidizing atmosphere and hydrosphere at approximately 2.0 billion years ago (through the niobium/uranium ratio). Increase in the niobium/thorium ratio shows involvement of hydrated lithosphere in differentiation of Earth since approximately 3.8 billion years ago. After approximately 2.0 billion years ago, the decreasing mantle thorium/uranium ratio portrays mainly preferential recycling of uranium in an oxidizing atmosphere and hydrosphere. Net growth rate of continental crust has varied over time, and continents are still growing today.
Present-Day Deformation Across the Basin and Range Province, Western United States
Authors: Thatcher Wayne , Foulger G. R. , Julian B. R. , Svarc J. , Quilty E. , Bawden G. W.
Published: July 2002

The distribution of deformation within the Basin and Range province was determined from 1992, 1996, and 1998 surveys of a dense, 800-kilometer–aperture, Global Positioning System network. Internal deformation generally follows the pattern of Holocene fault distribution and is concentrated near the western extremity of the province, with lesser amounts focused near the eastern boundary. Little net deformation occurs across the central 500 kilometers of the network in western Utah and eastern Nevada. Concentration of deformation adjacent to the rigid Sierra Nevada block indicates that external plate-driving forces play an important role in driving deformation, modulating the extensional stress field generated by internal buoyancy forces that are due to lateral density gradients and topography near the province boundaries.
Dipping Low-Velocity Layer in the Mid-Lower Mantle: Evidence for Geochemical Heterogeneity
Authors: Kaneshima Satoshi , Helffrich George
Published: July 2002

Data from western United States short-period seismic networks reveal a conversion from an
S
to a
P
wave within a low seismic velocity layer (greater than or equal to the 4 percent velocity difference compared to the surrounding mantle) in the mid–lower mantle (1400 to 1600 kilometers deep) east of the Mariana and Izu-Bonin subduction zones. The low-velocity layer (about 8 kilometers thick) dips 30° to 40° southward and is at least 500 kilometers by 300 kilometers. Its steep dip, large velocity contrast, and sharpness imply a chemical rather than a thermal origin. Ancient oceanic crust subducted into the lower mantle is a plausible candidate for the low-velocity layer because of its broad thin extent.
Chain Walking: A New Strategy to Control Polymer Topology
Authors: Guan Zhibin , Cotts P. M. , McCord E. F. , McLain S. J.
Published: July 2002

Ethylene pressure has been used to control the competition between isomerization (chain walking) and monomer insertion processes for ethylene coordination polymerization catalyzed by a palladium-α-diimine catalyst. The topology of the polyethylene varies from linear with moderate branching to “hyperbranched” structures. Although the overall branching number and the distribution of short-chain branching change very slightly, the architecture or topology of the polyethylene changes from linear polyethylene with moderate branches at high ethylene pressures to a hyperbranched polyethylene at low pressures.
Severe Liver Degeneration in Mice Lacking the IκB Kinase 2 Gene
Authors: Li Qiutang , Antwerp Daniel Van , Mercurio Frank , Lee Kuo-Fen , Verma Inder M.
Published: July 2002

Phosphorylation of inhibitor of kappa B (IκB) proteins is an important step in the activation of the transcription nuclear factor kappa B (NF-κB) and requires two IκB kinases, IKK1 (IKKα) and IKK2 (IKKβ). Mice that are devoid of the IKK2 gene had extensive liver damage from apoptosis and died as embryos, but these mice could be rescued by the inactivation of the gene encoding tumor necrosis factor receptor 1. Mouse embryonic fibroblast cells that were isolated from IKK2
–/–
embryos showed a marked reduction in tumor necrosis factor–α (TNF-α)– and interleukin-1α–induced NF-κB activity and an enhanced apoptosis in response to TNF-α. IKK1 associated with NF-κB essential modulator (IKKγ/IKKAP1), another component of the IKK complex. These results show that IKK2 is essential for mouse development and cannot be substituted with IKK1.
Magnetization Directions of Individual Nanoparticles
Authors: Majetich S. A. , Jin Y.
Published: July 2002

The magnetization directions of individual monodomain nanoparticles as small as 5 nanometers in diameter are determined using the Foucault method of Lorentz microscopy. A model is developed to explain the images and diffraction patterns of samarium cobalt nanoparticles as a function of the aperture shift direction. Thermally induced changes in the magnetization direction of superparamagnetic magnetite nanoparticles were observed but with a much slower rate than expected, due to surface anisotropy. When the time scale for magnetization reversal is much shorter than the data acquisition time, as in carbon-coated iron cobalt alloy nanoparticles, the images show an average of such thermally induced changes.
Systemic Signaling and Acclimation in Response to Excess Excitation Energy in
Arabidopsis
Authors: Karpinski Stanislaw , Reynolds Helen , Karpinska Barbara , Wingsle Gunnar , Creissen Gary , Mullineaux Philip
Published: July 2002

Land plants are sessile and have developed sophisticated mechanisms that allow for both immediate and acclimatory responses to changing environments. Partial exposure of low light–adapted
Arabidopsis
plants to excess light results in a systemic acclimation to excess excitation energy and consequent photooxidative stress in unexposed leaves. Thus, plants possess a mechanism to communicate excess excitation energy systemically, allowing them to mount a defense against further episodes of such stress. Systemic redox changes in the proximity of photosystem II, hydrogen peroxide, and the induction of antioxidant defenses are key determinants of this mechanism of systemic acquired acclimation.
Global Distribution of Crustal Magnetization Discovered by the Mars Global Surveyor MAG/ER Experiment
Authors: Acuña M. H. , Connerney J. E. P. , F. N. , Ness  , Lin R. P. , Mitchell D. , Carlson C. W. , McFadden J. , Anderson K. A. , Rème H. , Mazelle C. , Vignes D. , Wasilewski P. , Cloutier P.
Published: July 2002

Vector magnetic field observations of the martian crust were acquired by the Mars Global Surveyor (MGS) magnetic field experiment/electron reflectometer (MAG/ER) during the aerobraking and science phasing orbits, at altitudes between ∼100 and 200 kilometers. Magnetic field sources of multiple scales, strength, and geometry were observed. There is a correlation between the location of the sources and the ancient cratered terrain of the martian highlands. The absence of crustal magnetism near large impact basins such as Hellas and Argyre implies cessation of internal dynamo action during the early Naochian epoch (∼4 billion years ago). Sources with equivalent magnetic moments as large as 1.3 × 10
17
ampere-meter
2
in the Terra Sirenum region contribute to the development of an asymmetrical, time-variable obstacle to solar wind flow around Mars.
Magnetic Lineations in the Ancient Crust of Mars
Authors: Connerney J. E. P. , Acuña M. H. , Wasilewski P. J. , Ness N. F. , Rème H. , Mazelle C. , Vignes D. , Lin R. P. , Mitchell D. L. , Cloutier P. A.
Published: July 2002

The Mars Global Surveyor spacecraft, in a highly elliptical polar orbit, obtained vector magnetic field measurements above the surface of Mars (altitudes >100 kilometers). Crustal magnetization, mainly confined to the most ancient, heavily cratered martian highlands, is frequently organized in east-west–trending linear features, the longest extending over 2000 kilometers. Crustal remanent magnetization exceeds that of terrestrial crust by more than an order of magnitude. Groups of quasi-parallel linear features of alternating magnetic polarity were found. They are reminiscent of similar magnetic features associated with sea floor spreading and crustal genesis on Earth but with a much larger spatial scale. They may be a relic of an era of plate tectonics on Mars.
Emerging Infectious Diseases: Public Health Issues for the 21st Century
Authors: Binder Sue , Levitt Alexandra M. , Sacks Jeffrey J. , Hughes James M.
Published: July 2002

Infectious diseases are the third leading cause of death in the United States and the leading cause worldwide. As the new millennium approaches, the public health community must replenish capacity depleted during years of inadequate funding while simultaneously incorporating new technologies and planning for the longer term. Among the challenges facing the public health community is the need for coordinated, global, multisectoral approaches to preventing and controlling complex infectious disease problems.
Quantum Computing with Electrons Floating on Liquid Helium
Authors: Platzman P. M. , Dykman M. I.
Published: July 2002

A quasi–two-dimensional set of electrons (1 <
N
< 10
9
) in vacuum, trapped in one-dimensional hydrogenic levels above a micrometer-thick film of liquid helium, is proposed as an easily manipulated strongly interacting set of quantum bits. Individual electrons are laterally confined by micrometer-sized metal pads below the helium. Information is stored in the lowest hydrogenic levels. With electric fields, at temperatures of 10
−2
kelvin, changes in the wave function can be made in nanoseconds. Wave function coherence times are 0.1 millisecond. The wave function is read out with an inverted dc voltage, which releases excited electrons from the surface.
The Structural Era of Endocytosis
Authors: Marsh M. , McMahon H. T.
Published: July 2002

Endocytosis is crucial for an array of cellular functions and can occur through several distinct mechanisms with the capacity to internalize anything from small molecules to entire cells. The clathrin-mediated endocytic pathway has recently received considerable attention because of (i) the identification of an array of molecules that orchestrate the assembly of clathrin-coated vesicles and the selection of the vesicle cargo and (ii) the resolution of structures for a number of these proteins. Together, these data provide an initial three-dimensional framework for understanding the clathrin endocytic machinery.
Host Defense Mechanisms Triggered by Microbial Lipoproteins Through Toll-Like Receptors
Authors: Brightbill Hans D. , Libraty Daniel H. , Krutzik Stephan R. , Yang Ruey-Bing , Belisle John T. , Bleharski Joshua R. , Maitland Michael , Norgard Michael V. , Plevy Scott E. , Smale Stephen T. , Brennan Patrick J. , Bloom Barry R. , Godowski Paul J. , Modlin Robert L.
Published: July 2002

The generation of cell-mediated immunity against many infectious pathogens involves the production of interleukin-12 (IL-12), a key signal of the innate immune system. Yet, for many pathogens, the molecules that induce IL-12 production by macrophages and the mechanisms by which they do so remain undefined. Here it is shown that microbial lipoproteins are potent stimulators of IL-12 production by human macrophages, and that induction is mediated by Toll-like receptors (TLRs). Several lipoproteins stimulated TLR-dependent transcription of inducible nitric oxide synthase and the production of nitric oxide, a powerful microbicidal pathway. Activation of TLRs by microbial lipoproteins may initiate innate defense mechanisms against infectious pathogens.
Functional Characterization of the
S. cerevisiae
Genome by Gene Deletion and Parallel Analysis
Authors: Winzeler Elizabeth A. , Shoemaker Daniel D. , Astromoff Anna , Liang Hong , Anderson Keith , Andre Bruno , Bangham Rhonda , Benito Rocio , Boeke Jef D. , Bussey Howard , Chu Angela M. , Connelly Carla , Davis Karen , Dietrich Fred , Dow Sally Whelen , El Bakkoury Mohamed , Foury Françoise , Friend Stephen H. , Gentalen Erik , Giaever Guri , Hegemann Johannes H. , Jones Ted , Laub Michael , Liao Hong , Liebundguth Nicole , Lockhart David J. , Lucau-Danila Anca , Lussier Marc , M'Rabet Nasiha , Menard Patrice , Mittmann Michael , Pai Chai , Rebischung Corinne , Revuelta Jose L. , Riles Linda , Roberts Christopher J. , Ross-MacDonald Petra , Scherens Bart , Snyder Michael , Sookhai-Mahadeo Sharon , Storms Reginald K. , Véronneau Steeve , Voet Marleen , Volckaert Guido , Ward Teresa R. , Wysocki Robert , Yen Grace S. , Yu Kexin , Zimmermann Katja , Philippsen Peter , Johnston Mark , Davis Ronald W.
Published: July 2002

The functions of many open reading frames (ORFs) identified in genome-sequencing projects are unknown. New, whole-genome approaches are required to systematically determine their function. A total of 6925
Saccharomyces cerevisiae
strains were constructed, by a high-throughput strategy, each with a precise deletion of one of 2026 ORFs (more than one-third of the ORFs in the genome). Of the deleted ORFs, 17 percent were essential for viability in rich medium. The phenotypes of more than 500 deletion strains were assayed in parallel. Of the deletion strains, 40 percent showed quantitative growth defects in either rich or minimal medium.