bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular Manipulation of Microstructures: Biomaterials, Ceramics, and Semiconductors
Authors: Stupp Samuel I. , Braun Paul V.
Published: July 2002

Organic molecules can alter inorganic microstructures, offering a very powerful tool for the design of novel materials. In biological systems, this tool is often used to create microstructures in which the organic manipulators are a minority component. Three groups of materials—biomaterials, ceramics, and semiconductors—have been selected to illustrate this concept as used by nature and by synthetic laboratories exploring its potential in materials technology. In some of nature's biomaterials, macromolecules such as proteins, glycoproteins, and polysaccharides are used to control nucleation and growth of mineral phases and thus manipulate microstructure and physical properties. This concept has been used synthetically to generate apatite-based materials that can function as artificial bone in humans. Synthetic polymers and surfactants can also drastically change the morphology of ceramic particles, impart new functional properties, and provide new processing methods for the formation of useful objects. Interesting opportunities also exist in creating semiconducting materials in which molecular manipulators connect quantum dots or template cavities, which change their electronic properties and functionality.
Nanobeam Mechanics: Elasticity, Strength, and Toughness of Nanorods and Nanotubes
Authors: Wong Eric W. , Sheehan Paul E. , Lieber Charles M.
Published: July 2002

The Young's modulus, strength, and toughness of nanostructures are important to proposed applications ranging from nanocomposites to probe microscopy, yet there is little direct knowledge of these key mechanical properties. Atomic force microscopy was used to determine the mechanical properties of individual, structurally isolated silicon carbide (SiC) nanorods (NRs) and multiwall carbon nanotubes (MWNTs) that were pinned at one end to molybdenum disulfide surfaces. The bending force was measured versus displacement along the unpinned lengths. The MWNTs were about two times as stiff as the SiC NRs. Continued bending of the SiC NRs ultimately led to fracture, whereas the MWNTs exhibited an interesting elastic buckling process. The strengths of the SiC NRs were substantially greater than those found previously for larger SiC structures, and they approach theoretical values. Because of buckling, the ultimate strengths of the stiffer MWNTs were less than those of the SiC NRs, although the MWNTs represent a uniquely tough, energy-absorbing material.
Peripheral and Cerebral Asymmetries in the Rat
Authors: LaMendola Nicholas P. , Bever Thomas G.
Published: July 2002

Rats learn a novel foraging pattern better with their right-side whiskers than with their left-side whiskers. They also learn better with the left cerebral hemisphere than with the right hemisphere. Rotating an already learned maze relative to the external environment most strongly reduces right-whisker performance; starting an already learned maze at a different location most strongly reduces left-whisker performance. These results suggest that the right-periphery–left-hemisphere system accesses a map-like representation of the foraging problem, whereas the left-periphery–right-hemisphere system accesses a rote path. Thus, as in humans, functional asymmetries in rats can be elicited by both peripheral and cortical manipulation, and each hemisphere makes qualitatively distinct contributions to a complex natural behavior.
Active Deformation of Asia: From Kinematics to Dynamics
Authors: England Philip , Molnar Peter
Published: July 2002

Using estimated strain rates across the actively deforming region of Asia to infer variations in viscous stress, it is shown that gradients of stress point uphill toward the center of Tibet, where gravitational potential energy per unit surface area reaches a maximum. Thus, the dynamics of the deformation seem to obey the equation of creeping flow, which expresses a balance between gradients in stress and the gravitational body force. This balance, in the region of the Tibetan plateau, yields an estimate of 10
22
pascal second for the average viscosity of the Tibetan lithosphere, which is only about 10 to 100 times greater than the viscosity of the convecting upper mantle.
Developmental Patterns and the Identification of Homologies in the Avian Hand
Authors: Burke Ann C. , Feduccia Alan
Published: July 2002

Homologies of digits in the avian hand have been debated for 150 years. Cladistic analysis nests birds with theropod dinosaurs. Theropod hands retain only digits I-II-III, so digits of the modern bird hand are often identified as I-II-III. Study of the developing manus and pes in amniote embryos, including a variety of avian species, shows stereotyped patterns of cartilage condensations. A primary axis of cartilage condensation is visible in all species that runs through the humerus into digit IV. Comparison to serially homologous elements of the hindlimb indicates that the retained digits of the avian hand are II-III-IV.
Fyn-Kinase as a Determinant of Ethanol Sensitivity: Relation to NMDA-Receptor Function
Authors: Miyakawa Tsuyoshi , Yagi Takeshi , Kitazawa Hiromasa , Yasuda Masahiro , Kawai Nobufumi , Tsuboi Kenta , Niki Hiroaki
Published: July 2002

Animals vary in their sensitivity to ethanol, a trait at least partly determined by genetic factors. In order to identify possible responsible genes, mice lacking Fyn, a non–receptor type tyrosine kinase, were investigated. These mice were hypersensitive to the hypnotic effect of ethanol. The administration of ethanol enhanced tyrosine phosphorylation of the
N
-methyl-
d
-aspartate receptor (NMDAR) in the hippocampus of control mice but not in Fyn-deficient mice. An acute tolerance to ethanol inhibition of NMDAR-mediated excitatory postsynaptic potentials in hippocampal slices developed in control mice but not in Fyn-deficient mice. These results indicate that Fyn affects behavioral, biochemical, and physiological responses to ethanol.
Integrating Genetic Approaches into the Discovery of Anticancer Drugs
Authors: Hartwell Leland H. , Szankasi Philippe , Roberts Christopher J. , Murray Andrew W. , Friend Stephen H.
Published: July 2002

The discovery of anticancer drugs is now driven by the numerous molecular alterations identified in tumor cells over the past decade. To exploit these alterations, it is necessary to understand how they define a molecular context that allows increased sensitivity to particular compounds. Traditional genetic approaches together with the new wealth of genomic information for both human and model organisms open up strategies by which drugs can be profiled for their ability to selectively kill cells in a molecular context that matches those found in tumors. Similarly, it may be possible to identify and validate new targets for drugs that would selectively kill tumor cells with a particular molecular context. This article outlines some of the ways that yeast genetics can be used to streamline anticancer drug discovery.
Lung Structure and Ventilation in Theropod Dinosaurs and Early Birds
Authors: Ruben John A. , Jones Terry D. , Geist Nicholas R. , Hillenius W. Jaap
Published: July 2002

Reptiles and birds possess septate lungs rather than the alveolar-style lungs of mammals. The morphology of the unmodified, bellowslike septate lung restricts the maximum rates of respiratory gas exchange. Among taxa possessing septate lungs, only the modified avian flow-through lung is capable of the oxygen–carbon dioxide exchange rates that are typical of active endotherms. Paleontological and neontological evidence indicates that theropod dinosaurs possessed unmodified, bellowslike septate lungs that were ventilated with a crocodilelike hepatic-piston diaphragm. The earliest birds (
Archaeopteryx
and enantiornithines) also possessed unmodified septate lungs but lacked a hepatic-piston diaphragm mechanism. These data are consistent with an ectothermic status for theropod dinosaurs and early birds.
Impact of Molecular Order in Langmuir-Blodgett Films on Catalysis
Authors: Töllner Karl , Popovitz-Biro Ronit , Lahav Meir , Milstein David
Published: July 2002

Catalytically active Langmuir-Blodgett films of a rhodium complex were prepared and characterized to determine the possible effect of the molecular order of metal complexes on catalytic activity. The hydrogenation of carbon-oxygen double bonds was used as a model reaction. The complex in solution exhibited low catalytic activity, whereas it was highly active in the film. The catalytic activity was found to be highly dependent on the orientation of the complex within the film. The reactions were also highly selective with regard to the substrate. These observations and the observed rate dependence on temperature strongly implicate the molecular order of a metal complex as an important dimension in catalysis.
Quantitation of Transcription and Clonal Selection of Single Living Cells with β-Lactamase as Reporter
Authors: Zlokarnik Gregor , Negulescu Paul A. , Knapp Thomas E. , Mere Lora , Burres Neal , Feng Luxin , Whitney Michael , Roemer Klaus , Tsien Roger Y.
Published: July 2002

Gene expression was visualized in single living mammalian cells with β-lactamase as a reporter that hydrolyzes a substrate loaded intracellularly as a membrane-permeant ester. Each enzyme molecule changed the fluorescence of many substrate molecules from green to blue by disrupting resonance energy transfer. This wavelength shift was detectable by eye or color film in individual cells containing less than 100 β-lactamase molecules. The robust change in emission ratio reveals quantitative heterogeneity in real-time gene expression, enables clonal selection by flow cytometry, and forms a basis for high-throughput screening of pharmaceutical candidate drugs in living mammalian cells.
Isotopic Evidence for a Terrestrial Source of Organic Compounds Found in Martian Meteorites Allan Hills 84001 and Elephant Moraine 79001
Authors: Jull A. J. T. , Courtney C. , Jeffrey D. A. , Beck J. W.
Published: July 2002

Stepped-heating experiments on martian meteorites Allan Hills 84001 (ALH84001) and Elephant Moraine 79001 (EETA79001) revealed low-temperature (200 to 430 degrees Celsius) fractions with a carbon isotopic composition δ
13
C between −22 and −33 per mil and a carbon-14 content that is 40 to 60 percent of that of modern terrestrial carbon, consistent with a terrestrial origin for most of the organic material. Intermediate-temperature (400 to 600 degrees Celsius) carbonate-rich fractions of ALH84001 have δ
13
C of +32 to +40 per mil with a low carbon-14 content, consistent with an extraterrestrial origin, whereas some of the carbonate fraction of EETA79001 is terrestrial. In addition, ALH84001 contains a small preterrestrial carbon component of unknown origin that combusts at intermediate temperatures. This component is likely a residual acid-insoluble carbonate or a more refractory organic phase.
Fishing Down Marine Food Webs
Authors: Pauly Daniel , Christensen Villy , Dalsgaard Johanne , Froese Rainer , Torres Francisco
Published: July 2002

The mean trophic level of the species groups reported in Food and Agricultural Organization global fisheries statistics declined from 1950 to 1994. This reflects a gradual transition in landings from long-lived, high trophic level, piscivorous bottom fish toward short-lived, low trophic level invertebrates and planktivorous pelagic fish. This effect, also found to be occurring in inland fisheries, is most pronounced in the Northern Hemisphere. Fishing down food webs (that is, at lower trophic levels) leads at first to increasing catches, then to a phase transition associated with stagnating or declining catches. These results indicate that present exploitation patterns are unsustainable.
Src Activation in the Induction of Long-Term Potentiation in CA1 Hippocampal Neurons
Authors: Lu You Ming , Roder John C. , Davidow Jonathan , Salter Michael W.
Published: July 2002

Long-term potentiation (LTP) is an activity-dependent strengthening of synaptic efficacy that is considered to be a model of learning and memory. Protein tyrosine phosphorylation is necessary to induce LTP. Here, induction of LTP in CA1 pyramidal cells of rats was prevented by blocking the tyrosine kinase Src, and Src activity was increased by stimulation producing LTP. Directly activating Src in the postsynaptic neuron enhanced excitatory synaptic responses, occluding LTP. Src-induced enhancement of α-amino-3-hydroxy-5-methylisoxazolepropionic acid (AMPA) receptor–mediated synaptic responses required raised intracellular Ca
2+
and
N
-methyl-
d
-aspartate (NMDA) receptors. Thus, Src activation is necessary and sufficient for inducing LTP and may function by up-regulating NMDA receptors.
Dependence of BSAP Repressor and Activator Functions on BSAP Concentration
Authors: Wallin Jeffrey J. , Gackstetter Edwin R. , Elliott Koshland Marian
Published: July 2002

During a B cell immune response, the transcription factor BSAP maintains its activator functions but is relieved of its repressor functions. This selective targeting of BSAP activities was shown to be regulated by a concentration-dependent mechanism whereby activator motifs for BSAP had a 20-fold higher binding affinity than repressor motifs. An exchange of activator and repressor motifs, however, showed that the context of the motif, rather than the affinity, determined whether BSAP operated as an activator or repressor.
Supramolecular Structure of the
Salmonella typhimurium
Type III Protein Secretion System
Authors: Kubori Tomoko , Matsushima Yukiyasu , Nakamura Dai , Uralil Jaimol , Lara-Tejero Maria , Sukhan Anand , Galán Jorge E. , Aizawa Shin-Ichi
Published: July 2002

The type III secretion system of
Salmonella typhimurium
directs the translocation of proteins into host cells. Evolutionarily related to the flagellar assembly machinery, this system is also present in other pathogenic bacteria, but its organization is unknown. Electron microscopy revealed supramolecular structures spanning the inner and outer membranes of flagellated and nonflagellated strains; such structures were not detected in strains carrying null mutations in components of the type III apparatus. Isolated structures were found to contain at least three proteins of this secretion system. Thus, the type III apparatus of
S. typhimurium
, and presumably other bacteria, exists as a supramolecular structure in the bacterial envelope.
Reaction Sequence of Iron Sulfide Minerals in Bacteria and Their Use as Biomarkers
Authors: Pósfai Mihály , Buseck Peter R. , Bazylinski Dennis A. , Frankel Richard B.
Published: July 2002

Some bacteria form intracellular nanometer-scale crystals of greigite (Fe
3
S
4
) that cause the bacteria to be oriented in magnetic fields. Transmission electron microscope observations showed that ferrimagnetic greigite in these bacteria forms from nonmagnetic mackinawite (tetragonal FeS) and possibly from cubic FeS. These precursors apparently transform into greigite by rearrangement of iron atoms over a period of days to weeks. Neither pyrrhotite nor pyrite was found. These results have implications for the interpretation of the presence of pyrrhotite and greigite in the martian meteorite ALH84001.
COI1
: An
Arabidopsis
Gene Required for Jasmonate-Regulated Defense and Fertility
Authors: Xie Dao-Xin , Feys Bart F. , James Sarah , Nieto-Rostro Manuela , Turner John G.
Published: July 2002

The
coi1
mutation defines an
Arabidopsis
gene required for response to jasmonates, which regulate defense against insects and pathogens, wound healing, and pollen fertility. The wild-type allele,
COI1
, was mapped to a 90-kilobase genomic fragment and located by complementation of
coi1-1
mutants. The predicted amino acid sequence of the COI1 protein contains 16 leucine-rich repeats and an F-box motif. It has similarity to the F-box proteins
Arabidopsis
TIR1, human Skp2, and yeast Grr1, which appear to function by targeting repressor proteins for removal by ubiquitination.
Fullerene Pipes
Authors: Liu Jie , Rinzler Andrew G. , Dai Hongjie , Hafner Jason H. , Bradley R. Kelley , Boul Peter J. , Lu Adrian , Iverson Terry , Shelimov Konstantin , Huffman Chad B. , Rodriguez-Macias Fernando , Shon Young-Seok , Lee T. Randall , Colbert Daniel T. , Smalley Richard E.
Published: July 2002

Single-wall fullerene nanotubes were converted from nearly endless, highly tangled ropes into short, open-ended pipes that behave as individual macromolecules. Raw nanotube material was purified in large batches, and the ropes were cut into 100- to 300-nanometer lengths. The resulting pieces formed a stable colloidal suspension in water with the help of surfactants. These suspensions permit a variety of manipulations, such as sorting by length, derivatization, and tethering to gold surfaces.
Eating Disorders: Progress and Problems
Authors: Walsh B. Timothy , Devlin Michael J.
Published: July 2002

Recent research on Anorexia Nervosa and Bulimia Nervosa has yielded an increasingly detailed understanding of the range of biological and psychological abnormalities associated with these eating disorders. Inherited vulnerabilities, cultural pressures, and adverse individual and family experiences all appear to contribute to the onset of extreme dieting, binge eating, and purging. Once initiated, these behaviors give rise to multiple physiological disturbances, some of which may serve to perpetuate the illness. Although there have been substantial advances in the management of Bulimia Nervosa, the goal of offering effective treatment to all individuals with eating disorders remains elusive. This article reviews current thinking on the etiology and treatment of the two major eating disorders and a related syndrome, Binge Eating Disorder.
Ambiguities in Direct Dating of Rock Surfaces Using Radiocarbon Measurements
Authors: Beck W. , Donahue D. J. , Jull A. J. T. , Burr G. , Broecker W. S. , Bonani G. , Hajdas I. , Malotki E.
Published: July 2002

An attempt was made to date rock surfaces with accelerator mass spectrometry (AMS) radiocarbon measurements of rock varnishes or rock weathering rinds. In two case studies, samples pretreated in the laboratory of Dr. Ronald Dorn prior to AMS analysis have been found to contain significant quantities of carbon-rich materials of two distinct classes. Type I material resembles bituminous coal, whereas type II material resembles pyrolized wood charcoal fragments. In samples where these type I and type II materials were separated and AMS-radiocarbon dated, they were found to have widely differing radiocarbon ages. In these cases, the measurement of the radiocarbon age of the entire sample would yield results that are, at best, ambiguous. Neither type I nor type II materials were found in comparable samples that were independently prepared.
Delivery of Epitopes by the
Salmonella
Type III Secretion System for Vaccine Development
Authors: Rüssmann Holger , Shams Homayoun , Poblete Fernando , Fu Yixin , Galán Jorge E. , Donis Ruben O.
Published: July 2002

Avirulent strains of
Salmonella typhimurium
are being considered as antigen delivery vectors. During its intracellular stage in the host,
S. typhimurium
resides within a membrane-bound compartment and is not an efficient inducer of class I–restricted immune responses. Viral epitopes were successfully delivered to the host-cell cytosol by using the type III protein secretion system of
S. typhimurium
. This resulted in class I–restricted immune responses that protected vaccinated animals against lethal infection. This approach may allow the efficient use of
S. typhimurium
as an antigen delivery system to control infections by pathogens that require this type of immune response for protection.
Elastic Moduli of Wadsleyite (β-Mg
2
SiO
4
) to 7 Gigapascals and 873 Kelvin
Authors: Li Baosheng , Liebermann Robert C. , Weidner Donald J.
Published: July 2002

Simultaneous sound velocity measurements and x-ray diffraction studies were made on wadsleyite (β-Mg
2
SiO
4
) to 7 gigapascals and 873 kelvin. The calculated adiabatic bulk (
K
) and shear (
G
) moduli yield
K
(at room conditions) = 172(2) gigapascals,
dK
/
dP
= 4.2(1), and
dK
/
dT
= −0.012(1) gigapascals per kelvin, and
G
(at room conditions) = 113(1) gigapascals,
dG
/
dP
= 1.5(1), and
dG
/
dT
= −0.017(1) gigapascals per kelvin, respectively. The data imply that the
P
and
S
wave velocity contrasts between olivine and wadsleyite require an olivine amount of 38 to 39 percent in the upper mantle to satisfy the observed 410-kilometer discontinuity, but 55 to 60 percent to account for the velocity increase through the transition zone.
In Situ Observations of a High-Pressure Phase of H
2
O Ice
Authors: Chou I-Ming , Blank Jennifer G. , Goncharov Alexander F. , Mao Ho-kwang , Hemley Russell J.
Published: July 2002

A previously unknown solid phase of H
2
O has been identified by its peculiar growth patterns, distinct pressure-temperature melting relations, and vibrational Raman spectra. Morphologies of ice crystals and their pressure-temperature melting relations were directly observed in a hydrothermal diamond-anvil cell for H
2
O bulk densities between 1203 and 1257 kilograms per cubic meter at temperatures between –10° and 50°C. Under these conditions, four different ice forms were observed to melt: two stable phases, ice V and ice VI, and two metastable phases, ice IV and the new ice phase. The Raman spectra and crystal morphology are consistent with a disordered anisotropic structure with some similarities to ice VI.
RNA-Mediated Trans-Activation of Transcription from a Viral RNA
Authors: Sit Tim L. , Vaewhongs Andrew A. , Lommel Steven A.
Published: July 2002

The red clover necrotic mosaic virus genome is composed of two single-stranded RNA components, RNA-1 and RNA-2. The viral capsid protein is translated from a subgenomic RNA (sgRNA) that is transcribed from genomic RNA-1. Here, a 34-nucleotide sequence in RNA-2 is shown to be required for transcription of sgRNA. Mutations that prevent base-pairing between the RNA-1 subgenomic promoter and the 34-nucleotide trans-activator prevent expression of a reporter gene. A model is proposed in which direct binding of RNA-2 to RNA-1 trans-activates sgRNA synthesis. This RNA-mediated regulation of transcription is unusual among RNA viruses, which typically rely on protein regulators.
Crystal Structure of the Catalytic Domain of Human Plasmin Complexed with Streptokinase
Authors: Wang Xiaoqiang , Lin Xinli , Loy Jeffrey A. , Tang Jordan , Zhang Xuejun C.
Published: July 2002

Streptokinase is a plasminogen activator widely used in treating blood-clotting disorders. Complexes of streptokinase with human plasminogen can hydrolytically activate other plasminogen molecules to plasmin, which then dissolves blood clots. A similar binding activation mechanism also occurs in some key steps of blood coagulation. The crystal structure of streptokinase complexed with the catalytic unit of human plasmin was solved at 2.9 angstroms. The amino-terminal domain of streptokinase in the complex is hypothesized to enhance the substrate recognition. The carboxyl-terminal domain of streptokinase, which binds near the activation loop of plasminogen, is likely responsible for the contact activation of plasminogen in the complex.
Embryonic Stem Cell Lines Derived from Human Blastocysts
Authors: Thomson James A. , Itskovitz-Eldor Joseph , Shapiro Sander S. , Waknitz Michelle A. , Swiergiel Jennifer J. , Marshall Vivienne S. , Jones Jeffrey M.
Published: July 2002

Human blastocyst-derived, pluripotent cell lines are described that have normal karyotypes, express high levels of telomerase activity, and express cell surface markers that characterize primate embryonic stem cells but do not characterize other early lineages. After undifferentiated proliferation in vitro for 4 to 5 months, these cells still maintained the developmental potential to form trophoblast and derivatives of all three embryonic germ layers, including gut epithelium (endoderm); cartilage, bone, smooth muscle, and striated muscle (mesoderm); and neural epithelium, embryonic ganglia, and stratified squamous epithelium (ectoderm). These cell lines should be useful in human developmental biology, drug discovery, and transplantation medicine.
Sulfur Isotopic Composition of Cenozoic Seawater Sulfate
Authors: Paytan Adina , Kastner Miriam , Campbell Douglas , Thiemens Mark H.
Published: July 2002

A continuous seawater sulfate sulfur isotope curve for the Cenozoic with a resolution of ∼1 million years was generated using marine barite. The sulfur isotopic composition decreased from 19 to 17 per mil between 65 and 55 million years ago, increased abruptly from 17 to 22 per mil between 55 and 45 million years ago, remained nearly constant from 35 to ∼2 million years ago, and has decreased by 0.8 per mil during the past 2 million years. A comparison between seawater sulfate and marine carbonate carbon isotope records reveals no clear systematic coupling between the sulfur and carbon cycles over one to several millions of years, indicating that changes in the burial rate of pyrite sulfur and organic carbon did not singularly control the atmospheric oxygen content over short time intervals in the Cenozoic. This finding has implications for the modeling of controls on atmospheric oxygen concentration.
A Dielectric Omnidirectional Reflector
Authors: Fink Yoel , Winn Joshua N. , Fan Shanhui , Chen Chiping , Michel Jurgen , Joannopoulos John D. , Thomas Edwin L.
Published: July 2002

A design criterion that permits truly omnidirectional reflectivity for all polarizations of incident light over a wide selectable range of frequencies was used in fabricating an all-dielectric omnidirectional reflector consisting of multilayer films. The reflector was simply constructed as a stack of nine alternating micrometer-thick layers of polystyrene and tellurium and demonstrates omnidirectional reflection over the wavelength range from 10 to 15 micrometers. Because the omnidirectionality criterion is general, it can be used to design omnidirectional reflectors in many frequency ranges of interest. Potential uses depend on the geometry of the system. For example, coating of an enclosure will result in an optical cavity. A hollow tube will produce a low-loss, broadband waveguide, whereas a planar film could be used as an efficient radiative heat barrier or collector in thermoelectric devices.
Tracking the Long-Term Decline and Recovery of an Isolated Population
Authors: Westemeier Ronald L. , Brawn Jeffrey D. , Simpson Scott A. , Esker Terry L. , Jansen Roger W. , Walk Jeffery W. , Kershner Eric L. , Bouzat Juan L. , Paige Ken N.
Published: July 2002

Effects of small population size and reduced genetic variation on the viability of wild animal populations remain controversial. During a 35-year study of a remnant population of greater prairie chickens, population size decreased from 2000 individuals in 1962 to fewer than 50 by 1994. Concurrently, both fitness, as measured by fertility and hatching rates of eggs, and genetic diversity declined significantly. Conservation measures initiated in 1992 with translocations of birds from large, genetically diverse populations restored egg viability. Thus, sufficient genetic resources appear to be critical for maintaining populations of greater prairie chickens.
Identification of Two Distinct Mechanisms of Phagocytosis Controlled by Different Rho GTPases
Authors: Caron Emmanuelle , Hall Alan
Published: July 2002

The complement and immunoglobulin receptors are the major phagocytic receptors involved during infection. However, only immunoglobulin-dependent uptake results in a respiratory burst and an inflammatory response in macrophages. Rho guanosine triphosphatases (molecular switches that control the organization of the actin cytoskeleton) were found to be essential for both types of phagocytosis. Two distinct mechanisms of phagocytosis were identified: Type I, used by the immunoglobulin receptor, is mediated by Cdc42 and Rac, and type II, used by the complement receptor, is mediated by Rho. These results suggest a molecular basis for the different biological consequences that are associated with phagocytosis.
Identification of α-Dystroglycan as a Receptor for Lymphocytic Choriomeningitis Virus and Lassa Fever Virus
Authors: Cao Wei , Henry Michael D. , Borrow Persephone , Yamada Hiroki , Elder John H. , Ravkov Eugene V. , Nichol Stuart T. , Compans Richard W. , Campbell Kevin P. , Oldstone Michael B. A.
Published: July 2002

A peripheral membrane protein that is interactive with lymphocytic choriomeningitis virus (LCMV) was purified from cells permissive to infection. Tryptic peptides from this protein were determined to be α-dystroglycan (α-DG). Several strains of LCMV and other arenaviruses, including Lassa fever virus (LFV), Oliveros, and Mobala, bound to purified α-DG protein. Soluble α-DG blocked both LCMV and LFV infection. Cells bearing a null mutation of the gene encoding DG were resistant to LCMV infection, and reconstitution of DG expression in null mutant cells restored susceptibility to LCMV infection. Thus, α-DG is a cellular receptor for both LCMV and LFV.
Defective LPS Signaling in C3H/HeJ and C57BL/10ScCr Mice: Mutations in
Tlr4
Gene
Authors: Poltorak Alexander , He Xiaolong , Smirnova Irina , Liu Mu-Ya , Huffel Christophe Van , Du Xin , Birdwell Dale , Alejos Erica , Silva Maria , Galanos Chris , Freudenberg Marina , Ricciardi-Castagnoli Paola , Layton Betsy , Beutler Bruce
Published: July 2002

Mutations of the gene
Lps
selectively impede lipopolysaccharide (LPS) signal transduction in C3H/HeJ and C57BL/10ScCr mice, rendering them resistant to endotoxin yet highly susceptible to Gram-negative infection. The codominant
Lps

d

allele of C3H/HeJ mice was shown to correspond to a missense mutation in the third exon of the Toll-like receptor-4 gene (
Tlr4
), predicted to replace proline with histidine at position 712 of the polypeptide chain. C57BL/10ScCr mice are homozygous for a null mutation of
Tlr4
. Thus, the mammalian Tlr4 protein has been adapted primarily to subserve the recognition of LPS and presumably transduces the LPS signal across the plasma membrane. Destructive mutations of
Tlr4
predispose to the development of Gram-negative sepsis, leaving most aspects of immune function intact.
A Free-Fall Determination of the Newtonian Constant of Gravity
Authors: Schwarz Joshua P. , Robertson Douglas S. , Niebauer Timothy M. , Faller James E.
Published: July 2002

Recent determinations of the Newtonian constant of gravity have produced values that differ by nearly 40 times their individual error estimates (more than 0.5%). In an attempt to help resolve this situation, an experiment that uses the gravity field of a one-half metric ton source mass to perturb the trajectory of a free-falling mass and laser interferometry to track the falling object was performed. This experiment does not suspend the test mass from a support system. It is therefore free of many systematic errors associated with supports. The measured value was
G
= (6.6873 ± 0.0094) × 10
−11
m
3
kg
−1
sec
−2
.
Pleistocene Extinction of
Genyornis newtoni
: Human Impact on Australian Megafauna
Authors: Miller Gifford H. , Magee John W. , Johnson Beverly J. , Fogel Marilyn L. , Spooner Nigel A. , McCulloch Malcolm T. , Ayliffe Linda K.
Published: July 2002

More than 85 percent of Australian terrestrial genera with a body mass exceeding 44 kilograms became extinct in the Late Pleistocene. Although most were marsupials, the list includes the large, flightless mihirung
Genyornis newtoni
. More than 700 dates on
Genyornis
eggshells from three different climate regions document the continuous presence of
Genyornis
from more than 100,000 years ago until their sudden disappearance 50,000 years ago, about the same time that humans arrived in Australia. Simultaneous extinction of
Genyornis
at all sites during an interval of modest climate change implies that human impact, not climate, was responsible.
Humans Really Are Different
Authors: Shweder Richard A.
Published: July 2002

Three Seductive Ideas
. Jerome Kagan. Harvard University Press, Cambridge, MA, 1998. 240 pp. $27.50. ISBN 0-674-89033-7.

Kagan offers a "brilliant and provocative" critique of a wide range of popular ideas in the behavioral sciences, including ideas from evolutionary psychology, computational neuroscience, and cognitive ethology.
Crack Arrest and Multiple Cracking in Glass Through the Use of Designed Residual Stress Profiles
Authors: Green D. J. , Tandon R. , Sglavo V. M.
Published: July 2002

A processing approach has been identified and reduced to practice in which a residual stress profile can be designed such that cracks in a brittle material are arrested or grow in a stable manner. In the approach, cracks in the body encounter an increase in the magnitude of residual compression as the crack propagates. If correctly designed, the process increases strength and significantly decreases strength variability. This approach was demonstrated for a silicate glass, and multiple cracking was observed as a forewarning of the final failure. Normally, such glasses would fail catastrophically with the propagation of a dominant crack.
Electrostatic Deflections and Electromechanical Resonances of Carbon Nanotubes
Authors: Poncharal Philippe , Wang Z. L. , Ugarte Daniel , de Heer Walt A.
Published: July 2002

Static and dynamic mechanical deflections were electrically induced in cantilevered, multiwalled carbon nanotubes in a transmission electron microscope. The nanotubes were resonantly excited at the fundamental frequency and higher harmonics as revealed by their deflected contours, which correspond closely to those determined for cantilevered elastic beams. The elastic bending modulus as a function of diameter was found to decrease sharply (from about 1 to 0.1 terapascals) with increasing diameter (from 8 to 40 nanometers), which indicates a crossover from a uniform elastic mode to an elastic mode that involves wavelike distortions in the nanotube. The quality factors of the resonances are on the order of 500. The methods developed here have been applied to a nanobalance for nanoscopic particles and also to a Kelvin probe based on nanotubes.
Ice Core Records of Atmospheric CO
2
Around the Last Three Glacial Terminations
Authors: Fischer Hubertus , Wahlen Martin , Smith Jesse , Mastroianni Derek , Deck Bruce
Published: July 2002

Air trapped in bubbles in polar ice cores constitutes an archive for the reconstruction of the global carbon cycle and the relation between greenhouse gases and climate in the past. High-resolution records from Antarctic ice cores show that carbon dioxide concentrations increased by 80 to 100 parts per million by volume 600 ± 400 years after the warming of the last three deglaciations. Despite strongly decreasing temperatures, high carbon dioxide concentrations can be sustained for thousands of years during glaciations; the size of this phase lag is probably connected to the duration of the preceding warm period, which controls the change in land ice coverage and the buildup of the terrestrial biosphere.
Positive and Negative Regulation of IκB Kinase Activity Through IKKβ Subunit Phosphorylation
Authors: Delhase Mireille , Hayakawa Makio , Chen Yi , Karin Michael
Published: July 2002

IκB [inhibitor of nuclear factor κB (NF-κB)] kinase (IKK) phosphorylates IκB inhibitory proteins, causing their degradation and activation of transcription factor NF-κB, a master activator of inflammatory responses. IKK is composed of three subunits—IKKα and IKKβ, which are highly similar protein kinases, and IKKγ, a regulatory subunit. In mammalian cells, phosphorylation of two sites at the activation loop of IKKβ was essential for activation of IKK by tumor necrosis factor and interleukin-1. Elimination of equivalent sites in IKKα, however, did not interfere with IKK activation. Thus, IKKβ, not IKKα, is the target for proinflammatory stimuli. Once activated, IKKβ autophosphorylated at a carboxyl-terminal serine cluster. Such phosphorylation decreased IKK activity and may prevent prolonged activation of the inflammatory response.
Mechanism of Intrinsic Transcription Termination and Antitermination
Authors: Yarnell W. S. , Roberts J. W.
Published: July 2002

Gene expression is modulated by regulatory elements that influence transcription elongation by RNA polymerase: terminators that disrupt the elongation complex and release RNA, and regulators that overcome termination signals. RNA release from
Escherichia coli
RNA polymerase can be induced by a complementary oligonucleotide that replaces the upstream half of the RNA hairpin stem of intrinsic terminator transcripts, implying that RNA hairpins act by extracting RNA from the transcription complex. A transcription antiterminator inhibits this activity of oligonucleotides and therefore protects the elongation complex from destabilizing attacks on the emerging transcript. These effects illuminate the structure of the complex and the mechanism of transcription termination.
Male Homosexuality: Absence of Linkage to Microsatellite Markers at Xq28
Authors: Rice George , Anderson Carol , Risch Neil , Ebers George
Published: July 2002

Several lines of evidence have implicated genetic factors in homosexuality. The most compelling observation has been the report of genetic linkage of male homosexuality to microsatellite markers on the X chromosome. This observation warranted further study and confirmation. Sharing of alleles at position Xq28 was studied in 52 gay male sibling pairs from Canadian families. Four markers at Xq28 were analyzed (DXS1113, BGN, Factor 8, and DXS1108). Allele and haplotype sharing for these markers was not increased over expectation. These results do not support an X-linked gene underlying male homosexuality.
Electronically Configurable Molecular-Based Logic Gates
Authors: Collier C. P. , Wong E. W. , Belohradský M. , Raymo F. M. , Stoddart J. F. , Kuekes P. J. , Williams R. S. , Heath J. R.
Published: July 2002

Logic gates were fabricated from an array of configurable switches, each consisting of a monolayer of redox-active rotaxanes sandwiched between metal electrodes. The switches were read by monitoring current flow at reducing voltages. In the “closed” state, current flow was dominated by resonant tunneling through the electronic states of the molecules. The switches were irreversibly opened by applying an oxidizing voltage across the device. Several devices were configured together to produce AND and OR logic gates. The high and low current levels of those gates were separated by factors of 15 and 30, respectively, which is a significant enhancement over that expected for wired-logic gates.
Activation of NK Cells and T Cells by NKG2D, a Receptor for Stress-Inducible MICA
Authors: Bauer Stefan , Groh Veronika , Wu Jun , Steinle Alexander , Phillips Joseph H. , Lanier Lewis L. , Spies Thomas
Published: July 2002

Stress-inducible MICA, a distant homolog of major histocompatibility complex (MHC) class I, functions as an antigen for γδ T cells and is frequently expressed in epithelial tumors. A receptor for MICA was detected on most γδ T cells, CD8
+
αβ T cells, and natural killer (NK) cells and was identified as NKG2D. Effector cells from all these subsets could be stimulated by ligation of NKG2D. Engagement of NKG2D activated cytolytic responses of γδ T cells and NK cells against transfectants and epithelial tumor cells expressing MICA. These results define an activating immunoreceptor-MHC ligand interaction that may promote antitumor NK and T cell responses.
X-ray Structure of the FimC-FimH Chaperone-Adhesin Complex from Uropathogenic
Escherichia coli
Authors: Choudhury Devapriya , Thompson Andrew , Stojanoff Vivian , Langermann Solomon , Pinkner Jerome , Hultgren Scott J. , Knight Stefan D.
Published: July 2002

Type 1 pili—adhesive fibers expressed in most members of the Enterobacteriaceae family—mediate binding to mannose receptors on host cells through the FimH adhesin. Pilus biogenesis proceeds by way of the chaperone/usher pathway. The x-ray structure of the FimC-FimH chaperone-adhesin complex from uropathogenic
Escherichia coli
at 2.5 angstrom resolution reveals the basis for carbohydrate recognition and for pilus assembly. The carboxyl-terminal pilin domain of FimH has an immunoglobulin-like fold, except that the seventh strand is missing, leaving part of the hydrophobic core exposed. A donor strand complementation mechanism in which the chaperone donates a strand to complete the pilin domain explains the basis for both chaperone function and pilus biogenesis.
Equatorius
: A New Hominoid Genus from the Middle Miocene of Kenya
Authors: Ward Steve , Brown Barbara , Hill Andrew , Kelley Jay , Downs Will
Published: July 2002

A partial hominoid skeleton just older than 15 million years from sediments in the Tugen Hills of north central Kenya mandates a revision of the hominoid genus
Kenyapithecus
, a possible early member of the great ape–human clade. The Tugen Hills specimen represents a new genus, which also incorporates all material previously referable to
Kenyapithecus africanus
. The new taxon is derived with respect to earlier Miocene hominoids but is primitive with respect to the younger species
Kenyapithecus wickeri
and therefore is a late member of the stem hominoid radiation in the East African Miocene.
X-ray Crystal Structures of 70
S
Ribosome Functional Complexes
Authors: Cate Jamie H. , Yusupov Marat M. , Yusupova Gulnara Zh. , Earnest Thomas N. , Noller Harry F.
Published: July 2002

Structures of 70
S
ribosome complexes containing messenger RNA and transfer RNA (tRNA), or tRNA analogs, have been solved by x-ray crystallography at up to 7.8 angstrom resolution. Many details of the interactions between tRNA and the ribosome, and of the packing arrangements of ribosomal RNA (rRNA) helices in and between the ribosomal subunits, can be seen. Numerous contacts are made between the 30
S
subunit and the P-tRNA anticodon stem-loop; in contrast, the anticodon region of A-tRNA is much more exposed. A complex network of molecular interactions suggestive of a functional relay is centered around the long penultimate stem of 16
S
rRNA at the subunit interface, including interactions involving the “switch” helix and decoding site of 16
S
rRNA, and RNA bridges from the 50
S
subunit.
Defect-Mediated Condensation of a Charge Density Wave
Authors: Weitering Hanno H. , Carpinelli Joseph M. , Melechko Anatoli V. , Zhang Jiandi , Bartkowiak Miroslaw , Plummer E. Ward
Published: July 2002

Symmetry, dimensionality, and disorder play a pivotal role in critical phenomena. The atomic imaging capabilities of the scanning tunneling microscope were used to directly visualize the interaction between charge density oscillations and lattice defects in a two-dimensional charge density wave (CDW) system. Point defects act as nucleation centers of the CDW, which, as the temperature is lowered, results in the formation of pinned CDW domains that are separated by atomically abrupt charge boundaries. Incomplete freezing of substitutional disorder at low temperature indicates a novel CDW-mediated hopping of pinning centers.
Magma Intrusion Beneath Long Valley Caldera Confirmed by Temporal Changes in Gravity
Authors: Battaglia M. , Roberts C. , Segall P.
Published: July 2002

Precise relative gravity measurements conducted in Long Valley (California) in 1982 and 1998 reveal a decrease in gravity of as much as −107 ± 6 microgals (1 microgal = 10
−8
meters per square second) centered on the uplifting resurgent dome. A positive residual gravity change of up to 64 ± 15 microgals was found after correcting for the effects of uplift and water table fluctuations. Assuming a point source of intrusion, the density of the intruding material is 2.7 × 10
3
to 4.1 × 10
3
kilograms per cubic meter at 95 percent confidence. The gravity results require intrusion of silicate magma and exclude in situ thermal expansion or pressurization of the hydrothermal system as the cause of uplift and seismicity.
The Tyrosine Kinase Negative Regulator c-Cbl as a RING-Type, E2-Dependent Ubiquitin-Protein Ligase
Authors: Joazeiro Claudio A. P. , Wing Simon S. , Huang Han-kuei , Leverson Joel D. , Hunter Tony , Liu Yun-Cai
Published: July 2002

Ubiquitination of receptor protein-tyrosine kinases (RPTKs) terminates signaling by marking active receptors for degradation. c-Cbl, an adapter protein for RPTKs, positively regulates RPTK ubiquitination in a manner dependent on its variant SRC homology 2 (SH2) and RING finger domains. Ubiquitin-protein ligases (or E3s) are the components of ubiquitination pathways that recognize target substrates and promote their ligation to ubiquitin. The c-Cbl protein acted as an E3 that can recognize tyrosine-phosphorylated substrates, such as the activated platelet-derived growth factor receptor, through its SH2 domain and that recruits and allosterically activates an E2 ubiquitin-conjugating enzyme through its RING domain. These results reveal an SH2-containing protein that functions as a ubiquitin-protein ligase and thus provide a distinct mechanism for substrate targeting in the ubiquitin system.
Rapid and Reversible Effects of Activity on Acetylcholine Receptor Density at the Neuromuscular Junction in Vivo
Authors: Akaaboune Mohammed , Culican Susan M. , Turney Stephen G. , Lichtman Jeff W.
Published: July 2002

Quantitative fluorescence imaging was used to study the regulation of acetylcholine receptor (AChR) number and density at neuromuscular junctions in living adult mice. At fully functional synapses, AChRs have a half-life of about 14 days. However, 2 hours after neurotransmission was blocked, the half-life of the AChRs was now less than a day; the rate was 25 times faster than before. Most of the lost receptors were not quickly replaced. Direct muscle stimulation or restoration of synaptic transmission inhibited this process. AChRs that were removed from nonfunctional synapses resided for hours in the perijunctional membrane before being locally internalized. Dispersed AChRs could also reaggregate at the junction once neurotransmission was restored. The rapid and reversible alterations in AChR density at the neuromuscular junction in vivo parallel changes thought to occur in the central nervous system at synapses undergoing potentiation and depression.
Focal Adhesion Motility Revealed in Stationary Fibroblasts
Authors: Smilenov Lubomir B. , Mikhailov Alexei , Pelham Robert J. , Marcantonio Eugene E. , Gundersen Gregg G.
Published: July 2002

Focal adhesions (FAs) are clustered integrins and associated proteins that mediate cell adhesion and signaling. A green fluorescent protein–β1 integrin chimera was used to label FAs in living cells. In stationary cells, FAs were highly motile, moving linearly for several plaque lengths toward the cell center. FA motility was independent of cell density and resulted from contraction of associated actin fibers. In migrating cells, FAs were stationary and only moved in the tail. FA motility in stationary cells suggests that cell movement may be regulated by a clutch-like mechanism by which the affinity of integrins to substrate may be altered in response to migratory cues.
Imaging of Humic Substance Macromolecular Structures in Water and Soils
Authors: Myneni S. C. B. , Brown J. T. , Martinez G. A. , Meyer-Ilse W.
Published: July 2002

Humic substances (HSs) are the natural organic polyelectrolytes formed from the biochemical weathering of plant and animal remains. Their macromolecular structure and chemistry determine their role in biogeochemical processes. In situ spectromicroscopic evidence showed that the HS macromolecular structures (size and shape) vary as a function of HS origin (soil versus fluvial), solution chemistry, and the associated mineralogy. The HSs do not simply form coils in acidic or strong electrolyte solutions and elongated structures in dilute alkaline solutions. The macromolecular structural changes of HSs are likely to modify contaminant solubility, biotransformation, and the carbon cycle in soils and sediments.