bluuebunny/crossref_metadata_2025 huggingface dataset:
Tree Diversity in Tropical Rain Forests: A Validation of the Intermediate Disturbance Hypothesis
Authors: Molino Jean-François , Sabatier Daniel
Published: July 2002

The “intermediate disturbance hypothesis,” which postulates maximum diversity at intermediate regimes of disturbance, has never been clearly proved to apply to species-rich tropical forest tree communities and to local-scale canopy disturbances that modify light environments. This hypothesis was tested on a sample of 17,000 trees in a Guianan forest, 10 years after a silvicultural experiment that added to natural treefall gaps a wide range of disturbance intensities. Species richness, standardized to eliminate density effects, peaked at intermediate disturbance levels, particularly when disturbance intensity was estimated through the percentage of stems of strongly light-dependent species.
A Phosphatocopid Crustacean with Appendages from the Lower Cambrian
Authors: Siveter David J. , Williams Mark , Waloszek Dieter
Published: July 2002

Here we describe a phosphatocopid arthropod with preserved soft anatomy from Lower Cambrian rocks of Shropshire, England, which provides evidence for the occurrence of Crustacea, including Eucrustacea, in the Early Cambrian. The find identifies an important, stratigraphically early source of well-preserved fossils (Konservat-Lagerstätte).
Human Hypertension Caused by Mutations in WNK Kinases
Authors: Wilson Frederick H. , Disse-Nicodème Sandra , Choate Keith A. , Ishikawa Kazuhiko , Nelson-Williams Carol , Desitter Isabelle , Gunel Murat , Milford David V. , Lipkin Graham W. , Achard Jean-Michel , Feely Morgan P. , Dussol Bertrand , Berland Yvon , Unwin Robert J. , Mayan Haim , Simon David B. , Farfel Zvi , Jeunemaitre Xavier , Lifton Richard P.
Published: July 2002

Hypertension is a major public health problem of largely unknown cause. Here, we identify two genes causing pseudohypoaldosteronism type II, a Mendelian trait featuring hypertension, increased renal salt reabsorption, and impaired K
+
and H
+
excretion. Both genes encode members of the WNK family of serine-threonine kinases. Disease-causing mutations in
WNK1
are large intronic deletions that increase
WNK1
expression. The mutations in
WNK4
are missense, which cluster in a short, highly conserved segment of the encoded protein. Both proteins localize to the distal nephron, a kidney segment involved in salt, K
+
, and pH homeostasis. WNK1 is cytoplasmic, whereas WNK4 localizes to tight junctions. The WNK kinases and their associated signaling pathway(s) may offer new targets for the development of antihypertensive drugs.
Charge Migration in DNA: Ion-Gated Transport
Authors: Barnett Robert N. , Cleveland Charles L. , Joy Abraham , Landman Uzi , Schuster Gary B.
Published: July 2002

Electron hole (radical cation) migration in DNA, where the quantum transport of an injected charge is gated in a correlated manner by the thermal motions of the hydrated counterions, is described here. Classical molecular dynamics simulations in conjunction with large-scale first-principles electronic structure calculations reveal that different counterion configurations lead to formation of states characterized by varying spatial distributions and degrees of charge localization. Stochastic dynamic fluctuations between such ionic configurations can induce correlated changes in the spatial distribution of the hole, with concomitant transport along the DNA double helix. Comparative ultraviolet light–induced cleavage experiments on native B DNA oligomers and on ones modified to contain counterion (Na
+
)-starved bridges between damage-susceptible hole-trapping sites called GG steps show in the latter a reduction in damage at the distal step. This reduction indicates a reduced mobility of the hole across the modified bridge as predicted theoretically.
Spatiotemporal Addressing of Surface Activity
Authors: Wolff Janpeter , Papathanasiou Athanasios G. , Kevrekidis Ioannis G. , Rotermund Harm Hinrich , Ertl Gerhard
Published: July 2002

We have modified surface catalytic activity in real time and space by focusing an addressable laser beam to differentially heat a platinum (110) single-crystal surface. Ellipsomicroscopy imaging of local conditions (such as reactant and product local coverages) enabled us to close the loop between sensing and actuation (both spatiotemporally resolved). Pulses and fronts, the basic building blocks of patterns, could be formed, accelerated, modified, guided, and destroyed at will. Real-time image processing and feedback allow the design and implementation of new classes of nonlocal evolution rules.
Reproducible Measurement of Single-Molecule Conductivity
Authors: Cui X. D. , Primak A. , Zarate X. , Tomfohr J. , Sankey O. F. , Moore A. L. , Moore T. A. , Gust D. , Harris G. , Lindsay S. M.
Published: July 2002

A reliable method has been developed for making through-bond electrical contacts to molecules. Current-voltage curves are quantized as integer multiples of one fundamental curve, an observation used to identify single-molecule contacts. The resistance of a single octanedithiol molecule was 900 ± 50 megohms, based on measurements on more than 1000 single molecules. In contrast, nonbonded contacts to octanethiol monolayers were at least four orders of magnitude more resistive, less reproducible, and had a different voltage dependence, demonstrating that the measurement of intrinsic molecular properties requires chemically bonded contacts.
Nucleotide Variation Along the
Drosophila melanogaster
Fourth Chromosome
Authors: Wang Wen , Thornton Kevin , Berry Andrew , Long Manyuan
Published: July 2002

The
Drosophila melanogaster
fourth chromosome, believed to be nonrecombining and invariable, is a classic example of the effect of natural selection in eliminating genetic variation in linked loci. However, in a chromosome-wide assay of nucleotide variation in natural populations, we have observed a high level of polymorphism in a ∼200-kilobase region and marked levels of polymorphism in several other fragments interspersed with regions of little variation, suggesting different evolutionary histories in different chromosomal domains. Statistical tests of neutral evolution showed that a few haplotypes predominate in the 200-kilobase polymorphic region. Finally, contrary to the expectation of no recombination, we identified six recombination events within the chromosome. Thus, positive Darwinian selection and recombination have affected the evolution of this chromosome.
Preservation of Species Abundance in Marine Death Assemblages
Authors: Kidwell Susan M.
Published: July 2002

Fossil assemblages of skeletal material are thought to differ from their source live communities, particularly in relative abundance of species, owing to potential bias from postmortem transport and time-averaging of multiple generations. However, statistical meta-analysis of 85 marine molluscan data sets indicates that, although sensitive to sieve mesh-size and environment, time-averaged death assemblages retain a strong signal of species' original rank orders. Naturally accumulated death assemblages thus provide a reliable means of acquiring the abundance data that are key to a new generation of paleobiologic and macroecologic questions and to extending ecological time-series via sedimentary cores.
Tracking Femtosecond Laser Pulses in Space and Time
Authors: Balistreri M. L. M. , Gersen H. , Korterik J. P. , Kuipers L. , van Hulst N. F.
Published: July 2002

We show that the propagation of a femtosecond laser pulse inside a photonic structure can be directly visualized and tracked as it propagates using a time-resolved photon scanning tunneling microscope. From the time-dependent and phase-sensitive measurements, both the group velocity and the phase velocity are unambiguously and simultaneously determined. It is expected that this technique will find applications in the investigation of the local dynamic behavior of photonic crystals and integrated optical circuits.
Electrode-Reducing Microorganisms That Harvest Energy from Marine Sediments
Authors: Bond Daniel R. , Holmes Dawn E. , Tender Leonard M. , Lovley Derek R.
Published: July 2002

Energy in the form of electricity can be harvested from marine sediments by placing a graphite electrode (the anode) in the anoxic zone and connecting it to a graphite cathode in the overlying aerobic water. We report a specific enrichment of microorganisms of the family Geobacteraceae on energy-harvesting anodes, and we show that these microorganisms can conserve energy to support their growth by oxidizing organic compounds with an electrode serving as the sole electron acceptor. This finding not only provides a method for extracting energy from organic matter, but also suggests a strategy for promoting the bioremediation of organic contaminants in subsurface environments.
Structure of Haloform Intercalated C
60
and Its Influence on Superconductive Properties
Authors: Dinnebier Robert E. , Gunnarsson Olle , Brumm Holger , Koch Erik , Stephens Peter W. , Huq Ashfia , Jansen Martin
Published: July 2002

CHCl
3
and CHBr
3
intercalated C
60
have attracted particular interest after a superconductivity transition temperature (
T
c
) of up to 117 K was discovered. We have determined the structure using synchrotron x-ray powder-diffraction and found that the expansion of the lattice mainly takes place in one dimension (triclinic
b
axis), leaving planes of C
60
molecules on an approximately hexagonal, slightly expanded lattice. We have performed tight-binding band structure calculations for the surface layer. In spite of the slight expansion of the layers, for the range of dopings where a large
T
c
has been observed, the density of states at the Fermi energy is smaller for C
60
·2CHCl
3
and C
60
·2CHBr
3
than for C
60
. This suggests that the lattice expansion alone cannot explain the increase of
T
c
.
Laser-Induced Selectivity for Dimerization Versus Polymerization of Butadiene Under Pressure
Authors: Citroni Margherita , Ceppatelli Matteo , Bini Roberto , Schettino Vincenzo
Published: July 2002

The pressure-induced chemical reaction of liquid butadiene was studied by Fourier transform infrared spectroscopy in a diamond anvil cell. Dimerization was found to occur above 0.7 gigapascal, giving vinylcyclohexene according to a cyclo-addiction reaction and only a trace amount of polybutadiene forms. By irradiating the high-pressure sample with a few milliwatts of the 488-nanometer argon
+
laser line, the dimerization was completely inhibited, and the rapid formation of pure
trans
-polybutadiene was observed. The use of different excitation wavelength allows us to emphasize the selectivity of the process and to identify the active role of the 2
1
A
g
state in this pressure- and laser-induced chemical reaction.
Correlating Structural Dynamics and Function in Single Ribozyme Molecules
Authors: Zhuang Xiaowei , Kim Harold , Pereira Miguel J. B. , Babcock Hazen P. , Walter Nils G. , Chu Steven
Published: July 2002

We have studied the correlation between structural dynamics and function of the hairpin ribozyme. The enzyme-substrate complex exists in either docked (active) or undocked (inactive) conformations. Using single-molecule fluorescence methods, we found complex structural dynamics with four docked states of distinct stabilities and a strong memory effect where each molecule rarely switches between different docked states. We also found substrate cleavage to be rate-limited by a combination of conformational transitions and reversible chemistry equilibrium. The complex structural dynamics quantitatively explain the heterogeneous cleavage kinetics common to many catalytic RNAs. The intimate coupling of structural dynamics and function is likely a general phenomenon for RNA.
Enhanced and Delayed Stress-Induced Alcohol Drinking in Mice Lacking Functional CRH1 Receptors
Authors: Sillaber Inge , Rammes Gerhard , Zimmermann Stephan , Mahal Beatrice , Zieglgänsberger Walter , Wurst Wolfgang , Holsboer Florian , Spanagel Rainer
Published: July 2002

There is a relation between stress and alcohol drinking. We show that the corticotropin-releasing hormone (CRH) system that mediates endocrine and behavioral responses to stress plays a role in the control of long-term alcohol drinking. In mice lacking a functional CRH1 receptor, stress leads to enhanced and progressively increasing alcohol intake. The effect of repeated stress on alcohol drinking behavior appeared with a delay and persisted throughout life. It was associated with an up-regulation of the
N
-methyl-
d
-aspartate receptor subunit NR2B. Alterations in the CRH1 receptor gene and adaptional changes in NR2B subunits may constitute a genetic risk factor for stress-induced alcohol drinking and alcoholism.
Co-Seismic Strike-Slip and Rupture Length Produced by the 2001
M
s
8.1 Central Kunlun Earthquake
Authors: Lin Aiming , Fu Bihong , Guo Jianming , Zeng Qingli , Dang Guangming , He Wengui , Zhao Yue
Published: July 2002

Field investigations show that the surface wave magnitude (
M
s
) 8.1 Central Kunlun earthquake (Tibetan plateau) of 14 November 2001 produced a nearly 400-kilometer-long surface rupture zone, with as much as 16.3 meters of left-lateral strike-slip along the active Kunlun fault in northern Tibet. The rupture length and maximum displacement are the largest among the co-seismic surface rupture zones reported on so far. The strike-slip motion and the large rupture length generated by the earthquake indicate that the Kunlun fault partitions its deformation into an eastward extrusion of Tibet to accommodate the continuing penetration of the Indian plate into the Eurasian plate.
Neural Control of Voluntary Movement Initiation
Authors: Hanes Doug P. , Schall Jeffrey D.
Published: July 2002

When humans respond to sensory stimulation, their reaction times tend to be long and variable relative to neural transduction and transmission times. The neural processes responsible for the duration and variability of reaction times are not understood. Single-cell recordings in a motor area of the cerebral cortex in behaving rhesus monkeys (
Macaca mulatta
) were used to evaluate two alternative mathematical models of the processes that underlie reaction times. Movements were initiated if and only if the neural activity reached a specific and constant threshold activation level. Stochastic variability in the rate at which neural activity grew toward that threshold resulted in the distribution of reaction times. This finding elucidates a specific link between motor behavior and activation of neurons in the cerebral cortex.
From Peptide Precursors to Oxazole and Thiazole-Containing Peptide Antibiotics: Microcin B17 Synthase
Authors: Li Yue-Ming , Milne Jill C. , Madison Lara L. , Kolter Roberto , Walsh Christopher T.
Published: July 2002

Esherichia coli
microcin B17 is a posttranslationally modified peptide that inhibits bacterial DNA gyrase. It contains four oxazole and four thiazole rings and is representative of a broad class of pharmaceutically important natural products with five-membered heterocycles derived from peptide precursors. An in vitro assay was developed to detect heterocycle formation, and an enzyme complex, microcin B17 synthase, was purified and found to contain three proteins, McbB, McbC, and McbD, that convert 14 residues into the eight mono- and bisheterocyclic moieties in vitro that confer antibiotic activity on mature microcin B17. These enzymatic reactions alter the peptide backbone connectivity. The propeptide region of premicrocin is the major recognition determinant for binding and downstream heterocycle formation by microcin B17 synthase. A general pathway for the enzymatic biosynthesis of these heterocycles is formulated.
Diversification of C-Function Activity in Maize Flower Development
Authors: Mena Montaña , Ambrose Barbara A. , Meeley Robert B. , Briggs Steven P. , Yanofsky Martin F. , Schmidt Robert J.
Published: July 2002

The
Arabidopsis
gene
AGAMOUS
is required for male and female reproductive organ development and for floral determinacy. Reverse genetics allowed the isolation of a transposon-induced mutation in
ZAG1
, the maize homolog of
AGAMOUS
.
ZAG1
mutants exhibited a loss of determinacy, but the identity of reproductive organs was largely unaffected. This suggested a redundancy in maize sex organ specification that led to the identification and cloning of a second
AGAMOUS
homolog,
ZMM2
, that has a pattern of expression distinct from that of
ZAG1
. C-function organ identity in maize (as defined by the A, B, C model of floral organ development) may therefore be orchestrated by two closely related genes,
ZAG1
and
ZMM2
, with overlapping but nonidentical activities.
Influence of Nitrogen Loading and Species Composition on the Carbon Balance of Grasslands
Authors: Wedin David A. , Tilman David
Published: July 2002

In a 12-year experimental study of nitrogen (N) deposition on Minnesota grasslands, plots dominated by native warm-season grasses shifted to low-diversity mixtures dominated by cool-season grasses at all but the lowest N addition rates. This shift was associated with decreased biomass carbon (C):N ratios, increased N mineralization, increased soil nitrate, high N losses, and low C storage. In addition, plots originally dominated by nonnative cool-season grasses retained little added N and stored little C, even at low N input rates. Thus, grasslands with high N retention and C storage rates were the most vulnerable to species losses and major shifts in C and N cycling.
Capturing the Structure of a Catalytic RNA Intermediate: The Hammerhead Ribozyme
Authors: Scott William G. , Murray James B. , Arnold John R. P. , Stoddard Barry L. , Klug Aaron
Published: July 2002

The crystal structure of an unmodified hammerhead RNA in the absence of divalent metal ions has been solved, and it was shown that this ribozyme can cleave itself in the crystal when divalent metal ions are added. This biologically active RNA fold is the same as that found previously for two modified hammerhead ribozymes. Addition of divalent cations at low pH makes it possible to capture the uncleaved RNA in metal-bound form. A conformational intermediate, having an additional Mg(II) bound to the cleavage-site phosphate, was captured by freeze-trapping the RNA at an active pH prior to cleavage. The most significant conformational changes were limited to the active site of the ribozyme, and the changed conformation requires only small additional movements to reach a proposed transition-state.
Self-Assembly of Mesoscale Objects into Ordered Two-Dimensional Arrays
Authors: Bowden Ned , Terfort Andreas , Carbeck Jeff , Whitesides George M.
Published: July 2002

Regular arrays of topologically complex, millimeter-scale objects were prepared by self-assembly, with the shapes of the assembling objects and the wettability of their surfaces determining the structure of the arrays. The system was composed of solid objects floating at the interface between perfluorodecalin and water and interacting by lateral capillary forces; patterning of the wettability of the surfaces of the objects directs these forces. Self-assembly results from minimization of the interfacial free energy of the liquid-liquid interface. Calculations suggest that this strategy for self-assembly can be applied to objects on a micrometer scale.
Induction of Leaf Primordia by the Cell Wall Protein Expansin
Authors: Fleming Andrew J. , McQueen-Mason Simon , Mandel Therese , Kuhlemeier Cris
Published: July 2002

Expansins are extracellular proteins that increase plant cell wall extensibility in vitro. Beads loaded with purified expansin induced bulging on the leaf-generating organ, the apical meristem, of tomato plants. Some of these bulges underwent morphogenesis to produce leaflike structures, resulting in a reversal of the direction of phyllotaxis. Thus, expansin can induce tissue expansion in vivo, and localized control of tissue expansion may be sufficient to induce leaf formation. These results suggest a role for biophysical forces in the regulation of plant development.
An Aquaporin-Like Gene Required for the
Brassica
Self-Incompatibility Response
Authors: Ikeda Seishi , Nasrallah June B. , Dixit Ram , Preiss Susanne , Nasrallah Mikhail E.
Published: July 2002

Self-incompatibility in
Brassica
refers to the rejection of self-related pollen and is mediated by a receptor protein kinase localized to the plasma membrane of the stigma epidermis in the flower. The recessive mutation
mod
eliminates self-incompatibility in the stigma. In
mod
mutants, self-compatibility was shown to be associated with the absence of transcripts encoded by an aquaporin-related gene. This observation suggests that a water channel is required for the self-incompatibility response of
Brassica
, which is consistent with the concept that regulation of water transfer from the stigma to pollen is a checkpoint in the early events of pollination in the crucifer family.
Differential Effects of Early Hippocampal Pathology on Episodic and Semantic Memory
Authors: Vargha-Khadem F. , Gadian D. G. , Watkins K. E. , Connelly A. , Van Paesschen W. , Mishkin M.
Published: July 2002

Global anterograde amnesia is described in three patients with brain injuries that occurred in one case at birth, in another by age 4, and in the third at age 9. Magnetic resonance techniques revealed bilateral hippocampal pathology in all three cases. Remarkably, despite their pronounced amnesia for the episodes of everyday life, all three patients attended mainstream schools and attained levels of speech and language competence, literacy, and factual knowledge that are within the low average to average range. The findings provide support for the view that the episodic and semantic components of cognitive memory are partly dissociable, with only the episodic component being fully dependent on the hippocampus.
A G Protein-Coupled Receptor Phosphatase Required for Rhodopsin Function
Authors: Vinós Javier , Jalink Kees , Hardy Robert W. , Britt Steven G. , Zuker Charles S.
Published: July 2002

Heterotrimeric guanine nucleotide-binding protein (G protein)–coupled receptors are phosphorylated by kinases that mediate agonist-dependent receptor deactivation. Although many receptor kinases have been isolated, the corresponding phosphatases, necessary for restoring the ground state of the receptor, have not been identified.
Drosophila
RDGC (retinal degeneration C) is a phosphatase required for rhodopsin dephosphorylation in vivo. Loss of RDGC caused severe defects in the termination of the light response as well as extensive light-dependent retinal degeneration. These phenotypes resulted from the hyperphosphorylation of rhodopsin because expression of a truncated rhodopsin lacking the phosphorylation sites restored normal photoreceptor function. These results suggest the existence of a family of receptor phosphatases involved in the regulation of G protein–coupled signaling cascades.
Structure of a Murine Leukemia Virus Receptor-Binding Glycoprotein at 2.0 Angstrom Resolution
Authors: Fass Deborah , Davey Robert A. , Hamson Christian A. , Kim Peter S. , Cunningham James M. , Berger James M.
Published: July 2002

An essential step in retrovirus infection is the binding of the virus to its receptor on a target cell. The structure of the receptor-binding domain of the envelope glycoprotein from Friend murine leukemia virus was determined to 2.0 angstrom resolution by x-ray crystallography. The core of the domain is an antiparallel β sandwich, with two interstrand loops forming a helical subdomain atop the sandwich. The residues in the helical region, but not in the β sandwich, are highly variable among mammalian C-type retroviruses with distinct tropisms, indicating that the helical subdomain determines the receptor specificity of the virus.
Interdomain Interactions Underlying Activation of Cyclic Nucleotide-Gated Channels
Authors: Varnum Michael D. , Zagotta William N.
Published: July 2002

Cyclic nucleotide–gated (CNG) ion channels are multimeric proteins that activate in response to the binding of cyclic nucleotide to intracellular domains. Here, an intramolecular protein–protein interaction between the amino-terminal domain and the carboxyl-terminal ligand-binding domain of the rat olfactory CNG channel was shown to exert an autoexcitatory effect on channel activation. Calcium-calmodulin, which modulates CNG channel activity during odorant adaptation, blocked this interaction. A specific deletion within the amino-terminal domain disrupted the interdomain interaction in vitro and altered the gating properties and calmodulin sensitivity of expressed channels. Thus, the amino-terminal domain may promote channel opening by directly interacting with the carboxyl-terminal gating machinery; calmodulin regulates channel activity by targeting this interaction.
Preserved Acute Pain and Reduced Neuropathic Pain in Mice Lacking PKCγ
Authors: Malmberg Annika B. , Chen Chong , Tonegawa Susumu , Basbaum Allan I.
Published: July 2002

In normal animals, peripheral nerve injury produces a persistent, neuropathic pain state in which pain is exaggerated and can be produced by nonpainful stimuli. Here, mice that lack protein kinase C gamma (PKCγ) displayed normal responses to acute pain stimuli, but they almost completely failed to develop a neuropathic pain syndrome after partial sciatic nerve section, and the neurochemical changes that occurred in the spinal cord after nerve injury were blunted. Also, PKCγ was shown to be restricted to a small subset of dorsal horn neurons, thus identifying a potential biochemical target for the prevention and therapy of persistent pain.
Colliding Beam Fusion Reactor
Authors: Rostoker Norman , Binderbauer Michl W. , Monkhorst Hendrik J.
Published: July 2002

Recent results with Tokamak experiments provide insights into the problem of magnetic confinement. They demonstrate how to avoid anomalous transport and thus solve the major problems of Tokamak reactors: size, the production of 14-megaelectron volt neutrons, and maintenance. An alternate confinement system, the field-reversed configuration, confines beams of protons and boron-11. For the proton–boron-11 fusion reaction, the fusion products are all charged particles for which direct conversion is feasible and neutron flux is negligible.
Insolation Cycles as a Major Control of Equatorial Indian Ocean Primary Production
Authors: Beaufort Luc , Lancelot Yves , Camberlin Pierre , Cayre Olivia , Vincent Edith , Bassinot Franck , Labeyrie Laurent
Published: July 2002

Analysis of a continuous sedimentary record taken in the Maldives indicates that strong primary production fluctuations (70 to 390 grams of carbon per square meter per year) have occurred in the equatorial Indian Ocean during the past 910,000 years. The record of primary production is coherent and in phase with the February equatorial insolation, whereas it shows diverse phase behavior with δ
18
O, depending on the orbital frequency (eccentricity, obliquity, or precession) examined. These observations imply a direct control of productivity in the equatorial oceanic system by insolation. In the equatorial Indian Ocean, productivity is driven by the wind intensity of westerlies, which is related to the Southern Oscillation; therefore, it is suggested that a precession forcing on the Southern Oscillation is responsible for the observed paleoproductivity dynamics.
Protein Disulfide Isomerase as a Regulator of Chloroplast Translational Activation
Authors: Kim Jungmook , Mayfield Stephen P.
Published: July 2002

Light-regulated translation of chloroplast messenger RNAs (mRNAs) requires
trans-
acting factors that interact with the 5′ untranslated region (UTR) of these mRNAs. Chloroplast polyadenylate-binding protein (cPABP) specifically binds to the 5′-UTR of the
psbA
mRNA and is essential for translation of this mRNA. A protein disulfide isomerase that is localized to the chloroplast and copurifies with cPABP was shown to modulate the binding of cPABP to the 5′-UTR of the
psbA
mRNA by reversibly changing the redox status of cPABP through redox potential or adenosine 5′-diphosphate–dependent phosphorylation. This mechanism allows for a simple reversible switch regulating gene expression in the chloroplast.
Broad-Spectrum, Non-Opioid Analgesic Activity by Selective Modulation of Neuronal Nicotinic Acetylcholine Receptors
Authors: Bannon A. W. , Decker M. W. , Holladay M. W. , Curzon P. , Donnelly-Roberts D. , Puttfarcken P. S. , Bitner R. S. , Diaz A. , Dickenson A. H. , Porsolt R. D. , Williams M. , Arneric S. P.
Published: July 2002

Development of analgesic agents for the treatment of severe pain requires the identification of compounds that are devoid of opioid receptor liabilities. A potent (inhibition constant = 37 picomolar) neuronal nicotinic acetylcholine receptor (nAChR) ligand called ABT-594 was developed that has antinociceptive properties equal in efficacy to those of morphine across a series of diverse animal models of acute thermal, persistent chemical, and neuropathic pain states. These effects were blocked by the nAChR antagonist mecamylamine. In contrast to morphine, repeated treatment with ABT-594 did not appear to elicit opioid-like withdrawal or physical dependence. Thus, ABT-594 may be an analgesic that lacks the problems associated with opioid analgesia.
An
Arabidopsis
MADS Box Gene That Controls Nutrient-Induced Changes in Root Architecture
Authors: Zhang Hanma , Forde Brian G.
Published: July 2002

The development of plant root systems is sensitive to the availability and distribution of nutrients within the soil. For example, lateral roots proliferate preferentially within nitrate (NO
3
–
)-rich soil patches. A NO
3
−
-inducible
Arabidopsis
gene (
ANR1
), was identified that encodes a member of the MADS box family of transcription factors. Transgenic plants in which
ANR1
was repressed had an altered sensitivity to NO
3
–
and no longer responded to NO
3
–
-rich zones by lateral root proliferation, indicating that
ANR1
is a key determinant of developmental plasticity in
Arabidopsis
roots.
Gain-of-Function Mutations of c-
kit
in Human Gastrointestinal Stromal Tumors
Authors: Hirota Seiichi , Isozaki Koji , Moriyama Yasuhiro , Hashimoto Koji , Nishida Toshirou , Ishiguro Shingo , Kawano Kiyoshi , Hanada Masato , Kurata Akihiko , Takeda Masashi , Muhammad Tunio Ghulam , Matsuzawa Yuji , Kanakura Yuzuru , Shinomura Yasuhisa , Kitamura Yukihiko
Published: July 2002

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors in the human digestive tract, but their molecular etiology and cellular origin are unknown. Sequencing of c-
kit
complementary DNA, which encodes a proto-oncogenic receptor tyrosine kinase (KIT), from five GISTs revealed mutations in the region between the transmembrane and tyrosine kinase domains. All of the corresponding mutant KIT proteins were constitutively activated without the KIT ligand, stem cell factor (SCF). Stable transfection of the mutant c-
kit
complementary DNAs induced malignant transformation of Ba/F3 murine lymphoid cells, suggesting that the mutations contribute to tumor development. GISTs may originate from the interstitial cells of Cajal (ICCs) because the development of ICCs is dependent on the SCF-KIT interaction and because, like GISTs, these cells express both KIT and CD34.
Molecular Analysis of Cellulose Biosynthesis in
Arabidopsis
Authors: Arioli Tony , Peng Liangcai , Betzner Andreas S. , Burn Joanne , Wittke Werner , Herth Werner , Camilleri Christine , Höfte Herman , Plazinski Jacek , Birch Rosemary , Cork Ann , Glover Julie , Redmond John , Williamson Richard E.
Published: July 2002

Cellulose, an abundant, crystalline polysaccharide, is central to plant morphogenesis and to many industries. Chemical and ultrastructural analyses together with map-based cloning indicate that the
RSW1
locus of
Arabidopsis
encodes the catalytic subunit of cellulose synthase. The cloned gene complements the
rsw1
mutant whose temperature-sensitive allele is changed in one amino acid. The mutant allele causes a specific reduction in cellulose synthesis, accumulation of noncrystalline β-1,4-glucan, disassembly of cellulose synthase, and widespread morphological abnormalities. Microfibril crystallization may require proper assembly of the
RSW1
gene product into synthase complexes whereas glucan biosynthesis per se does not.
Fluorescent, Sequence-Selective Peptide Detection by Synthetic Small Molecules
Authors: Chen Chao-Tsen , Wagner Holger , Still W. Clark
Published: July 2002

Small organic sensor molecules were prepared that bind and signal the presence of unlabeled tripeptides in a sequence-selective manner. Sequence-selective peptide binding is a difficult problem because small peptides are highly flexible and there are no clear rules for designing peptide-binding molecules as there are for the nucleic acids. The signaling system involved the application of fluorescence energy transfer and provided large, real-time fluorescence increases (300 to 500 percent) upon peptide binding. With it, these sensors were sensitive enough to detect unlabeled cognate peptides both in organic solution and in the solid state at low micromolar concentrations.
Budding Yeast Cdc20: A Target of the Spindle Checkpoint
Authors: Hwang Lena H. , Lau Lucius F. , Smith Dana L. , Mistrot Cathy A. , Hardwick Kevin G. , Hwang Ellen S. , Amon Angelika , Murray Andrew W.
Published: July 2002

The spindle checkpoint regulates the cell division cycle by keeping cells with defective spindles from leaving mitosis. In the two-hybrid system, three proteins that are components of the checkpoint, Mad1, Mad2, and Mad3, were shown to interact with Cdc20, a protein required for exit from mitosis. Mad2 and Mad3 coprecipitated with Cdc20 at all stages of the cell cycle. The binding of Mad2 depended on Mad1 and that of Mad3 on Mad1 and Mad2. Overexpression of Cdc20 allowed cells with a depolymerized spindle or damaged DNA to leave mitosis but did not overcome the arrest caused by unreplicated DNA. Mutants in Cdc20 that were resistant to the spindle checkpoint no longer bound Mad proteins, suggesting that Cdc20 is the target of the spindle checkpoint.
Results from the Mars Global Surveyor Thermal Emission Spectrometer
Authors: Christensen P. R. , Anderson D. L. , Chase S. C. , Clancy R. T. , Clark R. N. , Conrath B. J. , Kieffer H. H. , Kuzmin R. O. , Malin M. C. , Pearl J. C. , Roush T. L. , Smith M. D.
Published: July 2002

The Thermal Emission Spectrometer spectra of low albedo surface materials suggests that a four to one mixture of pyroxene to plagioclase, together with about a 35 percent dust component provides the best fit to the spectrum. Qualitative upper limits can be placed on the concentration of carbonates (<10 percent), olivine (<10 percent), clay minerals (<20 percent), and quartz (<5 percent) in the limited regions observed. Limb observations in the northern hemisphere reveal low-lying dust hazes and detached water-ice clouds at altitudes up to 55 kilometers. At an aerocentric longitude of 224° a major dust storm developed in the Noachis Terra region. The south polar cap retreat was similar to that observed by Viking.
Viral Strategies of Immune Evasion
Authors: Ploegh Hidde L.
Published: July 2002

The vertebrate body is an ideal breeding ground for viruses and provides the conditions that promote their growth, survival, and transmission. The immune system evolved and deals with this challenge. Mutually assured destruction is not a viable evolutionary strategy; thus, the study of host-virus interactions provides not only a glimpse of life at immunity's edge, but it has also illuminated essential functions of the immune system, in particular, the area of major histocompatibility complex–restricted antigen presentation.
Unitary Control in Quantum Ensembles: Maximizing Signal Intensity in Coherent Spectroscopy
Authors: Glaser S. J. , Schulte-Herbrüggen T. , Sieveking M. , Schedletzky O. , Nielsen N. C. , Sørensen O. W. , Griesinger C.
Published: July 2002

Experiments in coherent magnetic resonance, microwave, and optical spectroscopy control quantum-mechanical ensembles by guiding them from initial states toward target states by unitary transformation. Often, the coherences detected as signals are represented by a non-Hermitian operator. Hence, spectroscopic experiments, such as those used in nuclear magnetic resonance, correspond to unitary transformations between operators that in general are not Hermitian. A gradient-based systematic procedure for optimizing these transformations is described that finds the largest projection of a transformed initial operator onto the target operator and, thus, the maximum spectroscopic signal. This method can also be used in applied mathematics and control theory.
Visualization of Specific B and T Lymphocyte Interactions in the Lymph Node
Authors: Garside Paul , Ingulli Elizabeth , Merica Rebecca R. , Johnson Julia G. , Noelle Randolph J. , Jenkins Marc K.
Published: July 2002

Early events in the humoral immune response were visualized in lymph nodes by simultaneous tracking of antigen-specific CD4 T and B cells after immunization. The T cells were initially activated in the T cell areas when the B cells were still randomly dispersed in the B cell–rich follicles. Both populations then migrated to the edges of the follicles and interacted there, resulting in CD154-dependent B cell proliferation and germinal center formation. These results provide visual documentation of cognate T-B cell interactions and localize them to the follicular border.
Principles for Sustainable Governance of the Oceans
Authors: Costanza Robert , Andrade Francisco , Antunes Paula , den Belt Marjan van , Boersma Dee , Boesch Donald F. , Catarino Fernando , Hanna Susan , Limburg Karin , Low Bobbi , Molitor Michael , Pereira Joáo Gil , Rayner Steve , Santos Rui , Wilson James , Young Michael
Published: July 2002

Pressures being exerted on the ocean ecosystems through overfishing, pollution, and environmental and climate change are increasing. Six core principles are proposed to guide governance and use of ocean resources and to promote sustainability. Examples of governance structures that embody these principles are given.
Atmospheric Residence Time of CH
3
Br Estimated from the Junge Spatial Variability Relation
Authors: Colman Jonah J. , Blake Donald R. , Rowland F. Sherwood
Published: July 2002

The atmospheric residence time for methyl bromide (CH
3
Br) has been estimated as 0.8 ± 0.1 years from its empirical spatial variability relative to C
2
H
6
, C
2
Cl
4
, CHCl
3
, and CH
3
Cl. This evaluation of the atmospheric residence time, based on Junge's 1963 general proposal, provides an estimate for CH
3
Br that is independent of source and sink estimates. Methyl bromide from combined natural and anthropogenic sources furnishes about half of the bromine that enters the stratosphere, where it plays an important role in ozone destruction. This residence time is consistent with the 0.7-year value recently calculated for CH
3
Br from the combined strength estimates for its known significant sinks.
Evidence Against Hydrogen-Based Microbial Ecosystems in Basalt Aquifers
Authors: Anderson Robert T. , Chapelle Francis H. , Lovley Derek R.
Published: July 2002

It has been proposed that hydrogen produced from basalt–ground-water interactions may serve as an energy source that supports the existence of microorganisms in the deep subsurface on Earth and possibly on other planets. However, experiments demonstrated that hydrogen is not produced from basalt at an environmentally relevant, alkaline pH. Small amounts of hydrogen were produced at a lower pH in laboratory incubations, but even this hydrogen production was transitory. Furthermore, geochemical considerations suggest that previously reported rates of hydrogen production cannot be sustained over geologically significant time frames. These findings indicate that hydrogen production from basalt–ground-water interactions may not support microbial metabolism in the subsurface.
Dual Modes of Aging in Mediterranean Fruit Fly Females
Authors: Carey James R. , Liedo Pablo , Müller Hans-Georg , Wang Jane-Ling , Vaupel James W.
Published: July 2002

The life history of medflies is characterized by two physiological modes with different demographic schedules of fertility and survival: a waiting mode in which both mortality and reproduction are low and a reproductive mode in which mortality is very low at the onset of egg laying but accelerates as eggs are laid. Medflies stay in waiting mode when they are fed only sugar. When fed protein, a scarce resource in the wild, medflies switch to reproductive mode. Medflies that switch from waiting to reproductive mode survive longer than medflies kept in either mode exclusively. An understanding of the physiological shift that occurs between the waiting and reproductive modes may yield information about the fundamental processes that determine longevity.
Direct Phosphorylation of IκB by IKKα and IKKβ: Discrimination Between Free and NF-κB-Bound Substrate
Authors: Zandi Ebrahim , Chen Yi , Karin Michael
Published: July 2002

A large protein complex mediates the phosphorylation of the inhibitor of κB (IκB), which results in the activation of nuclear factor κB (NF-κB). Two subunits of this complex, IκB kinase α (IKKα) and IκB kinase β (IKKβ), are required for NF-κB activation. Purified recombinant IKKα and IKKβ expressed in insect cells were used to demonstrate that each protein can directly phosphorylate IκB proteins. IKKα and IKKβ were found to form both homodimers and heterodimers. Both IKKα and IKKβ phosphorylated IκB bound to NF-κB more efficiently than they phosphorylated free IκB. This result explains how free IκB can accumulate in cells in which IKK is still active and thus can contribute to the termination of NF-κB activation.
Mechanisms of Directed Attention in the Human Extrastriate Cortex as Revealed by Functional MRI
Authors: Kastner Sabine , De Weerd Peter , Desimone Robert , Ungerleider Leslie G.
Published: July 2002

A typical scene contains many different objects, but the capacity of the visual system to process multiple stimuli at a given time is limited. Thus, attentional mechanisms are required to select relevant objects from among the many objects competing for visual processing. Evidence from functional magnetic resonance imaging (MRI) in humans showed that when multiple stimuli are present simultaneously in the visual field, their cortical representations within the object recognition pathway interact in a competitive, suppressive fashion. Directing attention to one of the stimuli counteracts the suppressive influence of nearby stimuli. This mechanism may serve to filter out irrelevant information in cluttered visual scenes.
The Chemistry of Water on Alumina Surfaces: Reaction Dynamics from First Principles
Authors: Hass Kenneth C. , Schneider William F. , Curioni Alessandro , Andreoni Wanda
Published: July 2002

Aluminas and their surface chemistry play a vital role in many areas of modern technology. The behavior of adsorbed water is particularly important and poorly understood. Simulations of hydrated α-alumina (0001) surfaces with ab initio molecular dynamics elucidate many aspects of this problem, especially the complex dynamics of water dissociation and related surface reactions. At low water coverage, free energy profiles established that molecularly adsorbed water is metastable and dissociates readily, even in the absence of defects, by a kinetically preferred pathway. Observations at higher water coverage revealed rapid dissociation and unanticipated collective effects, including water-catalyzed dissociation and proton transfer reactions between adsorbed water and hydroxide. The results provide a consistent interpretation of the measured coverage dependence of water heats of adsorption, hydroxyl vibrational spectra, and other experiments.
Attenuation of Virulence by Disruption of the
Mycobacterium tuberculosis erp
Gene
Authors: Berthet François-Xavier , Lagranderie Micheline , Gounon Pierre , Laurent-Winter Christine , Ensergueix Danielle , Chavarot Pierre , Thouron Françoise , Maranghi Eddie , Pelicic Vladimir , Portnoı̈ Denis , Marchal Gilles , Gicquel Brigitte
Published: July 2002

The virulence of the mycobacteria that cause tuberculosis depends on their ability to multiply in mammalian hosts. Disruption of the bacterial
erp
gene, which encodes the exported repetitive protein, impaired multiplication of
M. tuberculosis
and
M. bovis
Bacille Calmette-Guérin in cultured macrophages and mice. Reintroduction of
erp
into the mutants restored their ability to multiply. These results indicate that
erp
contributes to the virulence of
M. tuberculosis
.
TNF-α Induction of CD44-Mediated Leukocyte Adhesion by Sulfation
Authors: Maiti Arpita , Maki Guitta , Johnson Pauline
Published: July 2002

Regulation of cell adhesion is important for immune system function. CD44 is a tightly regulated cell adhesion molecule present on leukocytes and implicated in their attachment to endothelium during an inflammatory immune response. The proinflammatory cytokine tumor necrosis factor–α, but not interferon-γ, was found to convert CD44 from its inactive, nonbinding form to its active form by inducing the sulfation of CD44. This posttranslational modification was required for CD44-mediated binding to the extracellular matrix component hyaluronan and to vascular endothelial cells. Sulfation is thus a potential means of regulating CD44-mediated leukocyte adhesion at inflammatory sites.
Loss of Intraspecific Aggression in the Success of a Widespread Invasive Social Insect
Authors: Holway David A. , Suarez Andrew V. , Case Ted J.
Published: July 2002

Despite the innumerable ecological problems and large economic costs associated with biological invasions, the proximate causes of invasion success are often poorly understood. Here, evidence is provided that reduced intraspecific aggression and the concomitant abandonment of territorial behavior unique to introduced populations of the Argentine ant contribute to the elevated population densities directly responsible for its widespread success as an invader. In the laboratory, nonaggressive pairs of colonies experienced lower mortality and greater foraging activity relative to aggressive pairs. These differences translated into higher rates of resource retrieval, greater brood production, and larger worker populations.
Auxin-Dependent Cell Expansion Mediated by Overexpressed Auxin-Binding Protein 1
Authors: Jones Alan M. , Im Kyung-Hoam , Savka Michael A. , Wu Ming-Jing , DeWitt N. Gregory , Shillito Raymond , Binns Andrew N.
Published: July 2002

To test the hypothesis that auxin-binding protein 1 (ABP1) is a receptor controlling auxin-mediated plant cell expansion,
ABP1
complementary DNAs were expressed in a controllable fashion in tobacco plants and constitutively in maize cell lines. Induction of
Arabidopsis ABP1
expression in tobacco leaf strips resulted in an increased capacity for auxin-mediated cell expansion, whereas induction of ABP1 in intact plants resulted in leaves with a normal morphology, but larger cells. Similarly, constitutive expression of maize
ABP1
in maize cell lines conferred on them the capacity to respond to auxin by increasing cell size. These results support a role of ABP1 as an auxin receptor controlling plant growth.
Ultrastable Mesostructured Silica Vesicles
Authors: Kim Seong Su , Zhang Wenzhong , Pinnavaia Thomas J.
Published: July 2002

A family of mesoporous molecular sieves (denoted MSU-G) with vesiclelike hierarchical structures and unprecedented thermal (1000°C) and hydrothermal stabilities (more than 150 hours at 100°C) associated with high SiO
4
cross-linking was prepared through a supramolecular assembly pathway that relies on hydrogen bonding between electrically neutral gemini surfactants of the type C

n

H
2

n

+1
NH(CH
2
)
2
NH
2
and silica precursors derived from tetraethylorthosilicate. The vesicle shells are constructed of one or more undulated silica sheets that are about 3 nanometers thick with mesopores (average diameters from 2.7 to 4.0 nanometers) running both parallel and orthogonal to the silica sheets, which makes the framework structure bicontinuous and highly accessible. Catalytic metal ion centers [for example, Ti(IV) and Al(III)] have been incorporated into the framework with the retention of hierarchical structure.