bluuebunny/crossref_metadata_2025 huggingface dataset:
Inflammatory Bowel Disease and Adenomas in Mice Expressing a Dominant Negative N-Cadherin
Authors: Hermiston Michelle L. , Gordon Jeffrey I.
Published: October 2006

Cadherins mediate cell adhesion and are essential for normal development. Embryonic stem cells were transfected with a dominant negative N-cadherin mutant (NCADΔ) under the control of promoters active in small intestinal epithelial cells and then introduced into C57BL/6 mouse blastocysts. Analysis of adult chimeric mice revealed that expression of NCADΔ along the entire crypt-villus axis, but not in the villus epithelium alone, produced an inflammatory bowel disease resembling Crohn's disease. NCADΔ perturbed proliferation, migration, and death programs in crypts, which lead to adenomas. This model provides insights about cadherin function in an adult organ and the factors underlying inflammatory bowel disease and intestinal neoplasia.
Scientists Brace for Change As Ex-Communist Wins Election
Authors: Koenig Robert
Published: October 2006

Warsaw—The election of a former Communist as Poland's president on 19 November could strengthen the hand of leaders of the Polish Academy of Sciences, who have been arguing for more power over science funding. A recent report on Polish science by an international panel of experts recommended, however, that power be consolidated in a government agency established as part of the reforms that followed the collapse of the Communist government 5 years ago.
Ensemble Activity and Behavior—What's the Code?
Authors: Deadwyler Sam A. , Hampson Robert E.
Published: October 2006

The brain represents information in a distributed code, carried by action potentials in ensembles of neurons. Ensemble activity can now be monitored by multielectrode arrays in behaving animals. Deadwyler and Hampson describe recent results that illustrate how the brain may code behavior in ensembles of neurons.
Origin of Bilaterian Body Plans: Evolution of Developmental Regulatory Mechanisms
Authors: Davidson Eric H. , Peterson Kevin J. , Cameron R. Andrew
Published: October 2006

An argument is proposed to explain the origin of large metazoans, based on the regulatory processes that underlie the morphogenetic organization of pattern in modern animals. Genetic regulatory systems similar to those used in modern, indirectly developing marine invertebrates are considered to indicate the Precambrian regulatory platform on which were erected innovations that underlie the development of macroscopic body plans. Those systems are genetic regulatory programs that produce groups of unspecified “set-aside cells” and hierarchical regulatory programs that initially define regions of morphogenetic space in terms of domains of transcription factor expression. These ideas affect interpretation of the development of arthropods and chordates as well as interpretation of the role of the genes of the homeotic complex in embryogenesis.
Cation Dynamics and Diffusion in Lithium Orthosilicate: Two-Dimensional Lithium-6 NMR
Authors: Xu Zhi , Stebbins Jonathan F.
Published: October 2006

Many geological and technological processes depend on diffusion in crystalline silicates and oxides, but models of the dynamics of diffusion have only rarely been based on relatively direct microscopic information on the rates and energetics of the hopping of cations from site to site. Two-dimensional nuclear magnetic resonance (NMR) exchange spectra for lithium-6 in lithium orthosilicate (Li
4
SiO
4
) provided a detailed picture of the hopping rates of Li
+
ions among structurally distinct sites and helped to define the diffusion pathway. Rates and activation energies depended measurably on site geometry, and bulk electrical conductivity was accurately predicted.
Relation of the 1992 Landers, California, Earthquake Sequence to Seismic Scattering
Authors: Revenaugh Justin
Published: October 2006

Measurements of crustal scattering for the area surrounding the 1992 Landers earthquake sequence obtained from regional array recordings of teleseismic events for the 10-year period before the sequence showed that the slip distribution on faults could be deducible from the preshock elastic structure. Scattering intensity correlated strongly with the distribution of aftershocks and slip of the moment magnitude (
M
w
) 7.3 Landers main shock,
M
w
6.1 Joshua Tree, and
M
w
6.2 Big Bear events, which implies that aftershocks and slip are structurally controlled and broadly predictable. Scattering within the fault zones was directional and consistent with variable along-strike alignment of stress-induced cracks.
The Development of Crustacean Limbs and the Evolution of Arthropods
Authors: Panganiban Grace , Sebring Angela , Nagy Lisa , Carroll Sean
Published: October 2006

Arthropods exhibit great diversity in the position, number, morphology, and function of their limbs. The evolutionary relations among limb types and among the arthropod groups that bear them (insects, crustaceans, myriapods, and chelicerates) are controversial. Here, the use of molecular probes, including an antibody to proteins encoded by arthropod and vertebrate
Distal-less
(
Dll
and
Dlx
) genes, provided evidence that common genetic mechanisms underlie the development of all arthropod limbs and their branches and that all arthropods derive from a common ancestor. However, differences between crustacean and insect body plans were found to correlate with differences in the deployment of particular homeotic genes and in the ways that these genes regulate limb development.
Brain Researchers Speak a Common Language
Authors: Barinaga Marcia
Published: October 2006

San Diego—Among the feast of topics served up at this year's meeting of the Society for Neuroscience in San Diego were several reports dealing with how the brain processes language. Imaging studies of the human brain, as well as studies of songbirds, whose learning of song has some parallels with our learning of language, are shedding light on this uniquely human trait.
Measurements Are the Only Reality, Say Quantum Tests
Authors: Glanz James
Published: October 2006

Quantum mechanics insists that the characteristics of a particle or wave have no reality until they are measured, an idea that has long made physicists uncomfortable. New experiments suggest more strongly than ever that they will have to live with that discomfort. By studying pairs of photons that have correlated polarizations, a research group showed that the results make sense only if the polarizations do not exist apart from measurement.
Molecular Mimicry in Protein Synthesis?
Authors: Moore Peter B.
Published: October 2006

A Research Article in this issue of
Science
by P. Nissen
et al
. (
p. 1464
) reports the crystal structure of elongation factor Tu (EF-Tu) complexed with tRNA and GTP. In his Perspective, P. Moore discusses the similarity between this new structure and the GDP-bound form of elongation factor G. Three domains at the carboxyl-terminal end of EF-G, which have no homologs in EF-Tu, together resemble tRNA and are positioned like the tRNA bound to EF-Tu.
The Interstellar Carbon Budget and the Role of Carbon in Dust and Large Molecules
Authors: Snow Theodore P. , Witt Adolf N.
Published: October 2006

Published data on stellar composition show that carbon in the sun is substantially more abundant than in other stars. A carbon abundance of 225 carbon atoms per 10
6
hydrogen atoms is representative of galactic stars, whereas published values for the sun range from 350 to 470 carbon atoms per 10
6
hydrogen atoms. Other elements are also present in enhanced quantities in the solar system, consistent with suggestions that a supernova event was closely associated with the formation of the solar system. The overabundance of carbon in the solar system has many important implications, including new constraints on nucleosynthesis models for supernovae and substantial modification of the so-called “cosmic” composition normally adopted in discussions of galactic and interstellar abundances. A reduction in the galactic carbon budget, as suggested by the stellar composition data, strongly constrains the quantity of carbon that is available for the formation of interstellar dust, and some dust models now appear implausible because they require more carbon than is available.
Scaling Properties of Stretching Ridges in a Crumpled Elastic Sheet
Authors: Lobkovsky Alex , Gentges Sharon , Li Hao , Morse David , Witten T. A.
Published: October 2006

Strong deformation of a sheet of solid material often leads to a crumpled state having sharp points of high curvature. A scaling property governing the crumpled state has been numerically demonstrated by an examination of the ridges joining pairs of sharp points in a range of simple geometries of variable size. As the linear size
X
increases sufficiently, the deformation energy grows as
X
1/3
and consists of similar amounts of bending and stretching energy. The deformation energy becomes concentrated in a fraction of the sheet that decreases as
X
1/3
. Despite this concentration, the local strain in the ridge decreases as
X
2/3
. Nearly all the deformation energy in thin, crumpled elastic sheets was found to be concentrated in ridges that obey these scaling laws.
Activation of the Estrogen Receptor Through Phosphorylation by Mitogen-Activated Protein Kinase
Authors: Kato Shigeaki , Endoh Hideki , Masuhiro Yoshikazu , Kitamoto Takuya , Uchiyama Shimami , Sasaki Haruna , Masushige Shoichi , Gotoh Yukiko , Nishida Eisuke , Kawashima Hiroyuki , Metzger Daniel , Chambon Pierre
Published: October 2006

The phosphorylation of the human estrogen receptor (ER) serine residue at position 118 is required for full activity of the ER activation function 1 (AF-1). This Ser
118
is phosphorylated by mitogen-activated protein kinase (MAPK) in vitro and in cells treated with epidermal growth factor (EGF) and insulin-like growth factor (IGF) in vivo. Overexpression of MAPK kinase (MAPKK) or of the guanine nucleotide binding protein Ras, both of which activate MAPK, enhanced estrogen-induced and antiestrogen (tamoxifen)-induced transcriptional activity of wild-type ER, but not that of a mutant ER with an alanine in place of Ser
118
. Thus, the activity of the amino-terminal AF-1 of the ER is modulated by the phosphorylation of Ser
118
through the Ras-MAPK cascade of the growth factor signaling pathways.
Essential Ca
2+
-Binding Motif for Ca
2+
-Sensitive Inactivation of L-Type Ca
2+
Channels
Authors: de Leon Marita , Wang Yan , Jones Lisa , Perez-Reyes Edward , Wei Xiangyang , Soong Tuck Wah , Snutch Terry P. , Yue David T.
Published: October 2006

Intracellular calcium (Ca
2+
) inhibits the opening of L-type (α
1C
) Ca
2+
channels, providing physiological control of Ca
2+
entry into a wide variety of cells. A structural determinant of this Ca
2+
-sensitive inactivation was revealed by chimeric Ca
2+
channels derived from parental α
1C
and α
1E
channels, the latter of which is a neuronal channel lacking Ca
2+
inactivation. A consensus Ca
2+
-binding motif (an EF hand), located on the α
1C
subunit, was required for Ca
2+
inactivation. Donation of the α
1C
EF-hand region to the α
1E
channel conferred the Ca
2+
-inactivating phenotype. These results strongly suggest that Ca
2+
binding to the α
1C
subunit initiates Ca
2+
inactivation.
RNA Polymerase Gets Very Pushy
Authors: O'Brien Claire
Published: October 2006

RNA polymerase has to plow through sticky spots along a DNA strand to transcribe messenger RNA. How it does so has always been something of a mystery. As it turns out, the polymerase has one of the biggest motors around. Force measurements of the enzyme show it generates more power than even “traditional” motor proteins, and the measurement technique—which involves a trap known as an “optical tweezers”—may soon allow scientists to look at interactions between the enzyme and the DNA substrate in real-time.
Molecular Machines May Aid Gene Expression
Authors: Nowak Rachel
Published: October 2006

In order to pack all of the DNA into the chromosomes, the cells of higher organisms wrap it around a core of proteins called histones, much as thread is wound around a spool. But that makes the DNA hard to get at, raising questions about how the enzymes and other materials needed to copy the DNA into RNA, which is the first step in gene expression, might gain access to the DNA. Recent evidence now suggests that this is accomplished with the aid of molecular machines, energy-consuming proteins in the cell's nucleus, that disrupt the histones, allowing the gene-transcribing machinery in to do its job.
ENHANCED PERSPECTIVE: Small RNA Chaperones for Ribosome Biogenesis
Authors: Steitz Joan A. , Tycowski Kazimierz T.
Published: October 2006

The Howard Hughes Medical Institute, Department of Molecular Biophysics and Biochemistry, Yale University School of Medicine, New Haven, CT 06536-0812, USA. A set of small nuclear RNAs of 50 to 200 nucleotides resides in the nucleolus of the cell, the region of the nucleus in which ribosomes are made. J. A. Steitz and K. T. Tycowski discuss what is known about how these RNAs participate in the conversion of the long precursor RNAs to the mature 18
S
, 5.8
S
, and 28
S
rRNAs of the ribosome.
Three-Dimensional Simulation of a Magnitude 7.75 Earthquake on the San Andreas Fault
Authors: Olsen Kim B. , Archuleta Ralph J. , Matarese Joseph R.
Published: October 2006

Simulation of 2 minutes of long-period ground motion in the Los Angeles area with the use of a three-dimensional finite-difference method on a parallel supercomputer provides an estimate of the seismic hazard from a magnitude 7.75 earthquake along the 170-kilometer section of the San Andreas fault between Tejon Pass and San Bernardino. Maximum ground velocities are predicted to occur near the fault (2.5 meters per second) and in the Los Angeles basin (1.4 meters per second) where large amplitude surface waves prolong shaking for more than 60 seconds. Simulated spectral amplitudes for some regions within the Los Angeles basin are up to 10 times larger than those at sites outside the basin at similar distances from the San Andreas fault.
Defect Motion on an InP(110) Surface Observed with Noncontact Atomic Force Microscopy
Authors: Sugawara Yasuhiro , Ohta Masahiro , Ueyama Hitoshi , Morita Seizo
Published: October 2006

With an atomic force microscope operating in the noncontact mode in an ultrahigh vacuum, atomic-resolution imaging of the cleaved semi-insulating InP(110) surface has been achieved. By this method, atomic scale point defects and their motion were observed at room temperature, without the field-induced effects associated with scanning tunneling microscopy.
Mastering Nature's Strong Force
Authors: Taubes Gary
Published: October 2006

The strong force that holds quarks together to make up protons and neutrons has long defied theorists' calculations. Lately, however, with the help of years of supercomputer calculations, they have predicted the properties of hypothetical offspring of the strong force called glueballs—collections of gluons, the particles that transmit the strong force. Glimpses of glueballs in accelerator data are now confirming the predictions and telling theorists that their grasp of the force is sound.
Just Another Billion-Sun Black Hole
Authors: Finkbeiner Ann
Published: October 2006

By measuring the speed at which a disk of material is whirling at the center of a distant galaxy, astronomers have bagged their third supermassive black hole, this one in the galaxy NGC 4261. The observation, made with the Hubble Space Telescope, supports theorists' belief that a black hole powers the radiation emanating from the cores of active galaxies—the kind of galaxy that includes NGC 4261 and the two other known black-hole hosts. And it has set them to puzzling about how these black holes grew so big.
Materials Scientists Make Contact in Boston
Authors: Service Robert F.
Published: October 2006

Boston—Researchers looking to bring futuristic materials a step closer to reality gathered at the Materials Research Society meeting in Boston from 27 November to 1 December. One intriguing presentation focused on efforts to simplify computer-chip manufacture with a “rubber stamp” technique to press intricate circuits right onto a substrate; another talk reported that heating a thin film in alternating strips during manufacture improves its electrical conductivity dramatically.
The Molecular Biology of Rice
Authors: Shimamoto Ko
Published: October 2006

New developments in rice molecular biology are enabling its use as a paradigmatical model for monocotyledonous plants. K. Shimamoto discusses progress in the Rice Genome Project, the first positional cloning of a rice gene [also reported in this issue of
Science
(Song
et al
.,
p. 1804
)], and new cloning and transformation methods for rice.
High Photorefractive Gain in Nematic Liquid Crystals Doped with Electron Donor and Acceptor Molecules
Authors: Wiederrecht Gary P. , Yoon Beth A. , Wasielewski Michael R.
Published: October 2006

Liquid crystalline composite materials have been prepared that are strongly photorefractive. Nematic liquid crystals were doped with both electron donor and electron acceptor molecules that undergo facile, photoinduced, electron transfer reactions to yield mobile ions. A photorefractive gain ratio of 1.88 was observed. This gain ratio was achieved with low applied electric fields (0.4 kilovolts per centimeter) requiring only a 1.5-volt battery and low light intensities (100 milliwatts per square centimeter) in samples 37 to 88 micrometers thick that showed no loss in gain over a 6-month period.
Sodium Uptake by Puddling in a Moth
Authors: Smedley Scott R. , Eisner Thomas
Published: October 2006

Male Lepidoptera commonly visit stands of water to drink, a behavior known as puddling. Males of the notodontid moth
Gluphisia septentrionis
routinely puddle for hours, imbibing hundreds of gut-loads and voiding the fluid as repetitive anal jets. Cationic analyses showed puddling to lead to systemic sodium gain, a potential benefit to
Gluphisia
, whose larval food plant is low in sodium. Male
Gluphisia
are specialized for puddling, possessing a wide oral slit and a highly expanded enteric surface. The acquired sodium is transferred to the female at mating, for eventual incorporation into the eggs. Sodium acquisition may be the primary function of puddling in Lepidoptera.
A Nucleic Acid Triple Helix Formed by a Peptide Nucleic Acid-DNA Complex
Authors: Betts Laurie , Josey John A. , Veal James M. , Jordan Steven R.
Published: October 2006

The crystal structure of a nucleic acid triplex reveals a helix, designated P-form, that differs from previously reported nucleic acid structures. The triplex consists of one polypurine DNA strand complexed to a polypyrimidine hairpin peptide nucleic acid (PNA) and was successfully designed to promote Watson-Crick and Hoogsteen base pairing. The P-form helix is underwound, with a base tilt similar to B-form DNA. The bases are displaced from the helix axis even more than in A-form DNA. Hydrogen bonds between the DNA backbone and the Hoogsteen PNA backbone explain the observation that polypyrimidine PNA sequences form highly stable 2:1 PNA-DNA complexes. This structure expands the number of known stable helical forms that nucleic acids can adopt.
Planning for the Next Flu Pandemic
Authors: Pennisi Elizabeth
Published: October 2006

Although flu experts do not know exactly when the next great global flu epidemic will occur, they know that one is inevitable. Consequently, they are trying to work out a game plan that will enable them to recognize its onset and put preventive measures, such as vaccine programs, in place.
Search for Better Crystals Explores Inner, Outer Space
Authors: Normile Dennis
Published: October 2006

Hiroshima, Japan—Growing crystals of a protein for x-ray analysis of its structure is largely a matter of trial and error. But crystallographers meeting last month in Hiroshima got some good news about ways to make the process more reliable. The first detailed comparison of crystals grown in orbit with ones grown on Earth showed that space-grown crystals can approach perfection. And a clutch of new techniques presented at the meeting should speed the process of finding optimal crystal-growing conditions on Earth.
Medfly Transformed—Official!
Authors: Ashburner Michael
Published: October 2006

In this issue of
Science
, two reports (pp.
2002
and
2005
) describe the first successful transformation of the Mediterranean fruit fly, a serious pest for coffee and fruit growers. In his Perspective, M. Ashburner gives some historical background and explains why this may allow better control of this (and other) insects.
Plasmodesmata: Plant Channels for Molecules on the Move
Authors: Zambryski Patricia
Published: October 2006

Plant cells communicate with one another through plasmodesmata, cytoplasmic bridges that can carry metabolites and proteins. P. Zambryski discusses two papers in this week's issue of
Science
(pp.
1980
and
1983
), which show that plasmodesmata are inherently dynamic, altering their dimensions to increase their transport capability in response to viral or endogenous proteins, and that proteins travel to plasmodesmata on the cytoskeleton.
Interaction of Tobamovirus Movement Proteins with the Plant Cytoskeleton
Authors: Heinlein Manfred , Epel Bernard L. , Padgett Hal S. , Beachy Roger N.
Published: October 2006

The movement protein of tobacco mosaic tobamovirus and related viruses is essential for the cell-to-cell spread of infection and, in part, determines the host range of the virus. Movement protein (MP) was fused with the jellyfish green fluorescent protein (GFP), and a modified virus that contained this MP:GFP fusion protein retained infectivity. In protoplasts and leaf tissues, the MP:GFP fusion protein was detected as long filaments shortly after infection. Double-labeling fluorescence microscopy suggests that the MP interacts and coaligns with microtubules. The distribution of the MP is disrupted by treatments that disrupt microtubules, but not by cytochalasin B, which disrupts filamentous F-actin. Microtubules may target the MP to plasmodesmata, the intercellular channels that connect adjacent cells.
Inhibition of Leaf Senescence by Autoregulated Production of Cytokinin
Authors: Gan Susheng , Amasino Richard M.
Published: October 2006

Controlling expression of
IPT
, a gene encoding isopentenyl transferase (the enzyme that catalyzes the rate-limiting step in cytokinin biosynthesis), with a senescence-specific promoter results in the suppression of leaf senescence. Transgenic tobacco plants expressing this chimeric gene do not exhibit the developmental abnormalities usually associated with
IPT
expression because the system is autoregulatory. Because sufficient cytokinin is produced to retard senescence, the activity of the senescence-specific promoter is attenuated. Senescence-retarded leaves exhibit a prolonged, photosynthetically active life-span. This result demonstrates that endogenously produced cytokinin can regulate senescence and provides a system to specifically manipulate the senescence program.
The ARF1 GTPase-Activating Protein: Zinc Finger Motif and Golgi Complex Localization
Authors: Cukierman Edna , Huber Irit , Rotman Miriam , Cassel Dan
Published: October 2006

Hydrolysis of guanosine triphosphate (GTP) by the small guanosine triphosphatase (GTPase) adenosine diphosphate ribosylation factor-1 (ARF1) depends on a GTPase-activating protein (GAP). A complementary DNA encoding the ARF1 GAP was cloned from rat liver and predicts a protein with a zinc finger motif near the amino terminus. The GAP function required an intact zinc finger and additional amino-terminal residues. The ARF1 GAP was localized to the Golgi complex and was redistributed into a cytosolic pattern when cells were treated with brefeldin A, a drug that prevents ARF1-dependent association of coat proteins with the Golgi. Thus, the GAP is likely to be recruited to the Golgi by an ARF1-dependent mechanism.
Indonesian Policies Stymie Global Circulation Experiment
Authors: Mervis Jeffrey
Published: October 2006

Indonesia has blocked recent requests from foreign research vessels to enter its 200-nautical-mile Exclusive Economic Zone to take water samples for the World Ocean Circulation Experiment, a 30-nation collaboration on an international ocean circulation experiment. The refusals leave a gap in oceanographers' understanding of water flow between the Indian and Pacific oceans. And they illustrate a worldwide problem for oceanographers trying to study near-shore waters: Despite having international law on their side, they are seen as posing a threat to the host country.
Meeting Takes Pulse of Laser Accelerators
Authors: Glanz James
Published: October 2006

Louisville, Kentucky—Researchers around the world are sharpening their picture of the interplay between laser light and ionized gases, or plasmas. The phenomena are essential elements in the quest to put short-pulse lasers to use in practical devices such as accelerators.
Does Tellurium Frost Venus's Highlands?
Authors: Kerr Richard A.
Published: October 2006

Radar images of Venus present a puzzle: Why are the planet's highlands so bright? The bright patches, whose lower boundaries fall at the same altitude around the planet, look for all the world like terrestrial snow lines. Now a leading planetary scientist proposes that the reflective areas are a kind of snow: a frost of the exotic element tellurium, which freezes out of the atmosphere onto the planet's cooler highlands.
Supported Membranes: Scientific and Practical Applications
Authors: Sackmann E.
Published: October 2006

Scientific and practical applications of supported lipid-protein bilayers are described. Membranes can be covalently coupled to or separated from solids by ultrathin layers of water or soft polymer cushions. The latter systems maintain the structural and dynamic properties of free bilayers, forming a class of models of biomembranes that allow the application of a manifold of surface-sensitive techniques. They form versatile models of low-dimensionality complex fluids, which can be used to study interfacial forces and wetting phenomena, and enable the design of phantom cells to explore the interplay of lock-and-key forces (such as receptor-ligand binding) and universal forces for cell adhesion. Practical applications are the design of (highly selective) receptor surfaces of biosensors on electrooptical devices or the biofunctionalization of inorganic solids.
Vibration-Rotation Tunneling Spectra of the Water Pentamer: Structure and Dynamics
Authors: Liu K. , Brown M. G. , Cruzan J. D. , Saykally R. J.
Published: October 2006

Far-infrared laser vibration-rotation tunneling spectroscopy was used to measure an intermolecular vibration (81.19198 wave numbers) of the isolated water (D
2
O) pentamer. Rotational analysis supports the chiral, slightly puckered ring structure predicted by theory. The experimentally deduced interoxygen separations for the water clusters up to the pentamer showed exponential convergence toward the corresponding distance in bulk phase water.
Language Comprehension in Language-Learning Impaired Children Improved with Acoustically Modified Speech
Authors: Tallal Paula , Miller Steve L. , Bedi Gail , Byma Gary , Wang Xiaoqin , Nagarajan Srikantan S. , Schreiner Christoph , Jenkins William M. , Merzenich Michael M.
Published: October 2006

A speech processing algorithm was developed to create more salient versions of the rapidly changing elements in the acoustic waveform of speech that have been shown to be deficiently processed by language-learning impaired (LLI) children. LLI children received extensive daily training, over a 4-week period, with listening exercises in which all speech was translated into this synthetic form. They also received daily training with computer “games” designed to adaptively drive improvements in temporal processing thresholds. Significant improvements in speech discrimination and language comprehension abilities were demonstrated in two independent groups of LLI children.
Molecular Orientation and Two-Component Nature of the Crystalline Fraction of Spider Dragline Silk
Authors: Simmons Alexandra H. , Michal Carl A. , Jelinski Lynn W.
Published: October 2006

The molecular origin of the exceptional mechanical properties of spider silk is unclear. This paper presents solid-state
2
H nuclear magnetic resonance data from unoriented, oriented, and supercontracted fibers, indicating that the crystalline fraction of dragline silk consists of two types of alanine-rich regions, one that is highly oriented and one that is poorly oriented and less densely packed. A new model for the molecular-level structure of individual silk molecules and their arrangement in the fibers is proposed. These data suggest that it will be necessary to control the secondary structure of individual polymer molecules in order to obtain optimum properties in bio-inspired polymers.
1995 the Warmest Year? Yes and No
Authors: Kerr Richard A.
Published: October 2006

A month after a United Nations panel declared that the climate record of the last century shows subtle signs of greenhouse warming, the alarm bells rang again, as newspaper headlines highlighted 1995 as the hottest year ever. The margin, however, was so small as to be statistically insignificant. Climatologists are still waiting for a big surge in global temperature that might be an unequivocal sign of global warming.
Millennial Climate Oscillation Spied
Authors: Kerr Richard A.
Published: October 2006

Climate records stored in sea-floor sediments and glacial ice show that Earth's climate oscillates from warmer to cooler and back every 2000 years or so. Researchers had detected this oscillation during the last ice age but suspected it might somehow be driven by the great ice sheets. Now they have learned that the cycle has continued since the ice age, up to the present day, implying that something else drives it—perhaps a slow variation of the sun.
Physicists Produce First Anti-Atom
Authors: Watson Andrew
Published: October 2006

Researchers at CERN, the European center for particle physics in Geneva, have unveiled a piece of a looking-glass world by creating the first atoms of antimatter. Last fall they painstakingly combined positrons—antimatter counterparts of electrons—with antiprotons to make 11 short-lived atoms of antihydrogen. Antihydrogen should have exactly the same mass and optical properties as ordinary hydrogen, but researchers will be studying it to make sure; any deviations from this symmetry would shake the foundations of physics.
Approaching the Quantum Gate
Authors: Voss David
Published: October 2006

Quantum computers could potentially solve problems that conventional computers cannot. Constructing such a computer in reality, however, presents extreme challenges. As Voss discusses in his Perspective, two research groups have recently made important breakthroughs in building logic elements, which may someday be used in quantum computers.
Functional Evidence for Indirect Recognition of G·U in tRNA
Ala
by Alanyl-tRNA Synthetase
Authors: Gabriel K. , Schneider Jay , McClain William H.
Published: October 2006

The structural features of the G⋅U wobble pair in
Escherichia coli
alanine transfer RNA (tRNA
Ala
) that are associated with aminoacylation by alanyl-tRNA synthetase (AlaRS) were investigated in vivo for wild-type tRNA
Ala
and mutant tRNAs with G⋅U substitutions. tRNA
Ala
with G⋅U, C⋅A, or G⋅A gave similar amounts of charged tRNA
Ala
and supported viability of
E. coli
lacking chromosomal tRNA
Ala
genes. tRNA
Ala
with G⋅C was inactive. Recognition of G⋅U by AlaRS thus requires more than the functional groups on G⋅U in a regular helix and may involve detection of a helical distortion.
Social Status Sculpts Activity of Crayfish Neurons
Authors: Barinaga Marcia
Published: October 2006

While neurobiologists have long suspected that an animal's experiences must somehow change its nervous system, they have had little direct proof of that. Now researchers have identified a specific neuronal alteration that takes place in crayfish, depending on whether they are dominant or submissive. The work, which is described in a report on
page.366
, shows that the neuron that triggers the crayfish “tail-flip” reflex becomes much more responsive to the neurotransmitter serotonin in dominant crayfish than in submissive ones. Because the affected neuron is part of a well-studied neuronal circuit, neurobiologists should be able to unravel the molecular and cellular events by which the change occurs, as well as to ask how changes in this neuron and others combine to alter the animal's behavior.
Interfering With Atoms to Clear a Path for Lasers
Authors: Taubes Gary
Published: October 2006

A powerful laser beamed into a gas turns it, in essence, into a lens that either focuses the beam more intensely, until it splinters into filaments and hot spots, or defocuses and weakens it. This phenomenon—a vexing one for researchers and engineers—takes place because the light alters the electronic states of atoms in the medium, changing its refractive index. Now researchers have found a way to forestall this atomic response, allowing the laser to pass through unmolested.
Chromophores with Strong Heterocyclic Acceptors: A Poled Polymer with a Large Electro-Optic Coefficient
Authors: Ahlheim Markus , Barzoukas Marguerite , Bedworth Peter V. , Blanchard-Desce Mireille , Fort Alain , Hu Zhong-Ying , Marder Seth R. , Perry Joseph W. , Runser Claude , Staehelin Markus , Zysset Beat
Published: October 2006

Syntheses of a series of conjugated donor-acceptor chromophores, based on a strongly electron-withdrawing heterocyclic acceptor, have led to compounds with large second-order optical nonlinearities. Incorporation of one of these chromophores into polycarbonate at 20 percent weight loading yielded, after poling at 150 volts per micrometer, a polymer film with an electro-optic coefficient,
r
33
, of 55 picometers per volt at 1.313 micrometers. This value is roughly twice that of lithium niobate. A variant of one of these chromophores exhibited improved thermal stability as needed for use in polymers with higher glass transition temperatures. The chromophore was soluble in common organic solvents, had a scalar product of the dipole moment, μ, and the molecular first hyperpolarizability, β (corrected for dispersion), of roughly 5000 × 10
−48
electrostatic units, and showed less than 10 percent decomposition after heating for 20 minutes in air and at 200°C in an inert organic solvent.
Chaos and the Shapes of Elliptical Galaxies
Authors: Merritt David
Published: October 2006

Hubble Space Telescope observations reveal that the density of stars in most elliptical galaxies rises toward the center in a power-law cusp. Many of these galaxies also contain central dark objects, possibly supermassive black holes. The gravitational force from a steep cusp or black hole will destroy most of the box orbits that constitute the “backbone” of a triaxial stellar system. Detailed modeling demonstrates that the resulting chaos can preclude a self-consistent, strongly triaxial equilibrium. Most elliptical galaxies may therefore be nearly axisymmetric, either oblate or prolate.
C3d of Complement as a Molecular Adjuvant: Bridging Innate and Acquired Immunity
Authors: Dempsey Paul W. , Allison Michael E. D. , Akkaraju Srinivas , Goodnow Christopher C. , Fearon Douglas T.
Published: October 2006

An optimal immune response should differentiate between harmful and innocuous antigens. Primitive systems of innate immunity, such as the complement system, may play a role in this distinction. When activated, the C3 component of complement attaches to potential antigens on microorganisms. To determine whether this alters acquired immune recognition, mice were immunized with a recombinant model antigen, hen egg lysozyme (HEL), fused to murine C3d. HEL bearing two and three copies of C3d was 1000- and 10,000-fold more immunogenic, respectively, than HEL alone. Thus, C3d is a molecular adjuvant of innate immunity that profoundly influences an acquired immune response.
The Effect of Social Experience on Serotonergic Modulation of the Escape Circuit of Crayfish
Authors: Yeh Shih-Rung , Fricke Russell A. , Edwards Donald H.
Published: October 2006

The neuromodulator serotonin has widespread effects in the nervous systems of many animals, often influencing aggression and dominance status. In crayfish, the effect of serotonin on the neural circuit for tailflip escape behavior was found to depend on the animal's social experience. Serotonin reversibly enhanced the response to sensory stimuli of the lateral giant (LG) tailflip command neuron in socially dominant crayfish, reversibly inhibited it in subordinate animals, and persistently enhanced it in socially isolated crayfish. Serotonin receptor agonists had opposing effects: A vertebrate serotonin type 1 receptor agonist inhibited the LG neurons in dominant and subordinate crayfish and had no effect in isolates, whereas a vertebrate serotonin type 2 receptor agonist enhanced the LG neurons' responses in all three types of crayfish. The LG neurons appear to have at least two populations of serotonin receptors that differ in efficacy in dominant, subordinate, and socially isolate crayfish.
Modified Microbe May Boost TB Vaccine
Authors: Roush Wade
Published: October 2006

In its war against bacterial infections, one of medicine's longtime allies has been a member of the enemy: bacille Calmette-Guérin (BCG). The mycobacterium has been widely used as a vaccine against the tuberculosis (TB) organism. But BCG's protective effect varies greatly and wanes as people age. Now reinforcements may be on the way. Researchers have engineered a BCG strain to express mammalian cytokines, intercellular messengers that rally the immune system.
Regulation of Atmospheric O
2
: Feedback in the Microbial Feedbag
Authors: Kump Lee R. , Mackenzie Fred T.
Published: October 2006

We know from the geological record that the concentration of oxygen in the atmosphere is naturally regulated: Too much oxygen would have led to global destruction of forests by fire, but too little and any fire would have been unsustainable. But what is the mechanism of oxygen regulation? In their Perspective, Kump and Mackenzie discuss results presented in the same issue by Van Cappellen
et al
. (
p. 493
) suggesting that microbes in marine sediments play a crucial role in controlling oxygen levels.
Gating by Cyclic AMP: Expanded Role for an Old Signaling Pathway
Authors: Iyengar Ravi
Published: October 2006

The intracellular signal transduction pathway that utilizes cyclic AMP as a key messenger was the first such pathway to be described and has served as a model for many other transducing systems. Now Iyengar illustrates how this classic pathway has yet another function—in a number of different biological systems, the cyclic AMP pathway appears to gate (either negatively or positively) other signal transduction pathways.
BMP-1: Resurrection As Procollagen C-Proteinase
Authors: Reddi A. H.
Published: October 2006

The characterization of the function of bone morphogenetic protein-1 (BMP-1) was reported in last week's issue of
Science
(19 January, p. 360)
. In his Perspective, A. H. Reddi explains why it was surprising (and important) that BMP-1 turned out to be identical to procollagen C-proteinase, the enzyme responsible for triggering the self-assembly of collagen.
Molecular Cloning and Disease Association of Hepatitis G Virus: A Transfusion-Transmissible Agent
Authors: Linnen Jeff , Wages John , Zhang-Keck Zhen-Yong , Fry Kirk E. , Krawczynski Krzysztof Z. , Alter Harvey , Koonin Eugene , Gallagher Margaret , Alter Miriam , Hadziyannis Stephanos , Karayiannis Peter , Fung Kevin , Nakatsuji Yoshiyuki , Shih J. Wai-Kuo , Young Lavonne , Piatak Michael , Hoover Cameron , Fernandez John , Chen Stacie , Zou Jian-Chao , Morris Timothy , Hyams Kenneth C. , Ismay Susan , Lifson Jeffrey D. , Hess Georg , Foung Steven K. H. , Thomas Howard , Bradley Daniel , Margolis Harold , Kim Jungsuh P.
Published: October 2006

An RNA virus, designated hepatitis G virus (HGV), was identified from the plasma of a patient with chronic hepatitis. Extension from an immunoreactive complementary DNA clone yielded the entire genome (9392 nucleotides) encoding a polyprotein of 2873 amino acids. The virus is closely related to GB virus C (GBV-C) and distantly related to hepatitis C virus, GBV-A, and GBV-B. HGV was associated with acute and chronic hepatitis. Persistent viremia was detected for up to 9 years in patients with hepatitis. The virus is transfusion-transmissible. It has a global distribution and is present within the volunteer blood donor population in the United States.
Receptor-Ligand Interaction Between CD44 and Osteopontin (Eta-1)
Authors: Weber Georg F. , Ashkar Samy , Glimcher Melvin J. , Cantor Harvey
Published: October 2006

The CD44 family of surface receptors regulates adhesion, movement, and activation of normal and neoplastic cells. The cytokine osteopontin (Eta-1), which regulates similar cellular functions, was found to be a protein ligand of CD44. Osteopontin induces cellular chemotaxis but not homotypic aggregation, whereas the inverse is true for the interaction between CD44 and a carbohydrate ligand, hyaluronate. The different responses of cells after CD44 ligation by either osteopontin or hyaluronate may account for the independent effects of CD44 on cell migration and growth. This mechanism may also be exploited by tumor cells to promote metastasis formation.
Is the Dark Matter Mystery Solved?
Authors: Glanz James
Published: October 2006

San Antonio—A widely reported press conference at last month's meeting of the American Astronomical Society left the impression that the long-standing mystery of the identity of the universe's “dark matter” had been solved. At the meeting a multi-institutional team reported that it might consist of the ordinary matter contained in MACHO
s
, massive compact halo objects, rather than the exotic particles some theorists favor. But as even those team members concede, the number of MACHO sightings they've now made is still too small to come to a firm conclusion about whether they can account for all dark matter.
The Future of the Behavioral and Social Sciences
Authors: Smith Philip M. , Torrey Barbara Boyle
Published: October 2006

The scientific infrastructure in the behavioral and social sciences is not keeping up with public demands. The challenges for the sciences and the funders include making more efficient use of current data and improving longitudinal and international analyses. The sciences need continuity of funding, the setting of priorities in the funding, and rigorous training of the next generation of researchers.
Ion Channels: Opening the Gate
Authors: Kelner Katrina L.
Published: October 2006

A recent paper in
Science
(
12 Jan., p. 213
) and two papers in
Neuron
(H. P. Larsson
et al.
, in press, and N. Yang
et al.
, vol. 16, p. 113) demonstrate that a charged portion of the sodium and potassium ion channel (S4) moves in response to voltage changes across the membrane, consistent with its proposed role as a voltage sensor.
Lysosomal Degradation of Ubiquitin-Tagged Receptors
Authors: Hurtley Stella M.
Published: October 2006

Cytosolic proteins are tagged with the polypeptide ubiquitin for eventual destruction by the proteasome. A recent paper in
Cell
(L. Hicke and H. Riezman, vol. 84, p. 277) shows that in yeast ubiquitin also serves to tag membrane proteins for degradation by proteases in the vacuole, the yeast equivalent of the lysosome.
Surprises on the Way from One- to Two-Dimensional Quantum Magnets: The Ladder Materials
Authors: Dagotto Elbio , Rice T. M.
Published: October 2006

To make the transition from the quasi-long-range order in a chain of antiferromagnetically coupled
S
= 1/2 spins to the true long-range order that occurs in a plane, one can assemble chains to make ladders of increasing width. Surprisingly, this crossover between one and two dimensions is not at all smooth. Ladders with an even number of legs have purely short-range magnetic order and a finite energy gap to all magnetic excitations. Predictions of this ground state have now been verified experimentally. Holes doped into these ladders are predicted to pair and possibly superconduct.
Water-in-Carbon Dioxide Microemulsions: An Environment for Hydrophiles Including Proteins
Authors: Johnston K. P. , Harrison K. L. , Clarke M. J. , Howdle S. M. , Heitz M. P. , Bright F. V. , Carlier C. , Randolph T. W.
Published: October 2006

Carbon dioxide in the liquid and supercritical fluid states is useful as a replacement for toxic organic solvents. However, nonvolatile hydrophilic substances such as proteins, ions, and most catalysts are insoluble. This limitation was overcome by the formation of aqueous microemulsion droplets in a carbon dioxide-continuous phase with a nontoxic ammonium carboxylate perfluoropolyether surfactant. Several spectroscopic techniques consistently indicated that the properties of the droplets approach those of bulk water. The protein bovine serum albumin (BSA) with a molecular weight of 67,000 is soluble in this microemulsion and experiences an environment similar to that of native BSA in buffer.
Large-Scale Storms in Saturn's Atmosphere During 1994
Authors: Sanchez-Lavega A. , Lecacheux J. , Gomez J. M. , Colas F. , Laques P. , Noll K. , Gilmore D. , Miyazaki I. , Parker D.
Published: October 2006

Large-scale storms are rarely observed in Saturn's atmosphere, but their appearance traces the wind velocity field, providing information on the vertical structure of the clouds and on the dynamics of the atmosphere. Two large-scale atmospheric disturbances formed by clouds highly reflective in the visible part of the spectrum were observed on Saturn during 1994. An equatorial disturbance with a longitudinal size of ∼27,000 kilometers drifted in longitude with a velocity of 273.6 meters per second. A second disturbance, a rapidly evolving convective storm with an initial size ∼7000 kilometers, was observed at 56 degrees south, moving with a zonal velocity of 15.5 meters per second.
Identification of a Putative Target for Rho as the Serine-Threonine Kinase Protein Kinase N
Authors: Amano Mutsuki , Mukai Hideyuki , Ono Yoshitaka , Chihara Kazuyasu , Matsui Takeshi , Hamajima Yuko , Okawa Katsuya , Iwamatsu Akihiro , Kaibuchi Kozo
Published: October 2006

Rho, a Ras-like small guanosine triphosphatase, has been implicated in cytoskeletal responses to extracellular signals such as lysophosphatidic acid (LPA) to form stress fibers and focal contacts. The form of RhoA bound to guanosine triphosphate directly bound to and activated a serine-threonine kinase, protein kinase N (PKN). Activated RhoA formed a complex with PKN and activated it in COS-7 cells. PKN was phosphorylated in Swiss 3T3 cells stimulated with LPA, and this phosphorylation was blocked by treatment of cells with botulinum C3 exoenzyme. Activation of Rho may be linked directly to a serine-threonine kinase pathway.
Genetic Engineering Turns to Trees
Authors: Moffat Anne Simon
Published: October 2006

Even as researchers look for desirable tree genes that could be used for genetic engineering of trees, they are already introducing genes from other species, such as bacterial genes that confer insect resistance, into trees as a way of improving their quality. Other genetic manipulations might speed flowering or decrease production of lignin, a material that must be removed during paper-making.
Indeterminate Organization of the Visual System
Authors: Hilgetag Claus-C. , O'Neill Mark A. , Young Malcolm P.
Published: October 2006

The classic view of how the brain areas that control vision are connected is a complicated wiring diagram devised by manual sorting on the basis of existing anatomical data [D. J. Felleman and D. C. Van Essen,
Cereb. Cortex
1
, 1 (1991)]. Now, in this issue's Enhanced Perspective,
Hilgetag and co-workers
have used a computer algorithm to test whether there is a better way to organize the connections. They find that the brain is surprisingly indeterminate, and that no single hierarchy can satisfactorily represent the order implied by the anatomical data.

A more
detailed explanation
of their analysis and a
list of predictions
derived from their hierarchies that will be particularly informative to test experimentally can be found on the home page of the authors.