bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamics of Water Molecules in Aqueous Solvation Shells
Authors: Kropman M. F. , Bakker H. J.
Published: July 2002

We report on the direct measurement of the dynamics of water molecules in the solvation shell of an ion in aqueous solution. The hydrogen-bond dynamics of water molecules solvating a Cl
−
, Br
−
, or I
−
anion is slow compared with neat liquid water, indicating that the aqueous solvation shells of these ions are rigid. This rigidity can play an important role in the overall dynamics of chemical reactions in aqueous solution. The experiments were performed with femtosecond midinfrared nonlinear spectroscopy, because this technique allows the spectral response of the water molecules in the solvation shell to be distinguished clearly from that of the other water molecules in the solution.
A p53 Amino-Terminal Nuclear Export Signal Inhibited by DNA Damage-Induced Phosphorylation
Authors: Zhang Yanping , Xiong Yue
Published: July 2002

The p53 protein is present in low amounts in normally growing cells and is activated in response to physiological insults. MDM2 regulates p53 either through inhibiting p53's transactivating function in the nucleus or by targeting p53 degradation in the cytoplasm. We identified a previously unknown nuclear export signal (NES) in the amino terminus of p53, spanning residues 11 to 27 and containing two serine residues phosphorylated after DNA damage, which was required for p53 nuclear export in colloboration with the carboxyl-terminal NES. Serine-15–phosphorylated p53 induced by ultraviolet irradiation was not exported. Thus, DNA damage–induced phosphorylation may achieve optimal p53 activation by inhibiting both MDM2 binding to, and the nuclear export of, p53.
Trends, Rhythms, and Aberrations in Global Climate 65 Ma to Present
Authors: Zachos James , Pagani Mark , Sloan Lisa , Thomas Ellen , Billups Katharina
Published: July 2002

Since 65 million years ago (Ma), Earth's climate has undergone a significant and complex evolution, the finer details of which are now coming to light through investigations of deep-sea sediment cores. This evolution includes gradual trends of warming and cooling driven by tectonic processes on time scales of 10
5
to 10
7
years, rhythmic or periodic cycles driven by orbital processes with 10
4
- to 10
6
-year cyclicity, and rare rapid aberrant shifts and extreme climate transients with durations of 10
3
to 10
5
years. Here, recent progress in defining the evolution of global climate over the Cenozoic Era is reviewed. We focus primarily on the periodic and anomalous components of variability over the early portion of this era, as constrained by the latest generation of deep-sea isotope records. We also consider how this improved perspective has led to the recognition of previously unforeseen mechanisms for altering climate.
The Archean Dongwanzi Ophiolite Complex, North China Craton: 2.505-Billion-Year-Old Oceanic Crust and Mantle
Authors: Kusky Timothy M. , Li Jiang-Hai , Tucker Robert D.
Published: July 2002

We report a thick, laterally extensive 2505 ± 2.2–million-year-old (uranium-lead ratio in zircon) Archean ophiolite complex in the North China craton. Basal harzburgite tectonite is overlain by cumulate ultramafic rocks, a mafic-ultramafic transition zone of interlayered gabbro and ultramafic cumulates, compositionally layered olivine-gabbro and pyroxenite, and isotropic gabbro. A sheeted dike complex is rooted in the gabbro and overlain by a mixed dike–pillow lava section, chert, and banded iron formation. The documentation of a complete Archean ophiolite implies that mechanisms of oceanic crustal accretion similar to those of today were in operation by 2.5 billion years ago at divergent plate margins and that the temperature of the early mantle was not extremely elevated, as compared to the present-day temperature. Plate tectonic processes similar to those of the present must also have emplaced the ophiolite in a convergent margin setting.
Haplotype Variation and Linkage Disequilibrium in 313 Human Genes
Authors: Stephens J. Claiborne , Schneider Julie A. , Tanguay Debra A. , Choi Julie , Acharya Tara , Stanley Scott E. , Jiang Ruhong , Messer Chad J. , Chew Anne , Han Jin-Hua , Duan Jicheng , Carr Janet L. , Lee Min Seob , Koshy Beena , Kumar A. Madan , Zhang Ge , Newell William R. , Windemuth Andreas , Xu Chuanbo , Kalbfleisch Theodore S. , Shaner Sandra L. , Arnold Kevin , Schulz Vincent , Drysdale Connie M. , Nandabalan Krishnan , Judson Richard S. , Ruaño Gualberto , Vovis Gerald F.
Published: July 2002

Variation within genes has important implications for all biological traits. We identified 3899 single nucleotide polymorphisms (SNPs) that were present within 313 genes from 82 unrelated individuals of diverse ancestry, and we organized the SNPs into 4304 different haplotypes. Each gene had several variable SNPs and haplotypes that were present in all populations, as well as a number that were population-specific. Pairs of SNPs exhibited variability in the degree of linkage disequilibrium that was a function of their location within a gene, distance from each other, population distribution, and population frequency. Haplotypes generally had more information content (heterozygosity) than did individual SNPs. Our analysis of the pattern of variation strongly supports the recent expansion of the human population.
Developmental Changes Due to Long-Distance Movement of a Homeobox Fusion Transcript in Tomato
Authors: Kim Minsung , Canio Wynnelena , Kessler Sharon , Sinha Neelima
Published: July 2002

Long-distance movement of RNA through the phloem is known to occur, but the functional importance of these transported RNAs has remained unclear. Grafting experiments with a naturally occurring dominant gain-of-function leaf mutation in tomato were used to demonstrate long-distance movement of mutant messenger RNA (mRNA) into wild-type scions. The stock-specific pattern of mRNA expression was graft transmissible, indicating that the mRNA accumulation pattern is inherent to the transcript and not attributable to the promoter. The translocated mRNA caused changes in leaf morphology of the wild-type scions, suggesting that the translocated RNA is functional.
High-Resolution X-ray Imaging of a Globular Cluster Core: Compact Binaries in 47Tuc
Authors: Grindlay Jonathan E. , Heinke Craig , Edmonds Peter D. , Murray Stephen S.
Published: July 2002

We have obtained high-resolution (≲1") deep x-ray images of the globular cluster 47Tucanae (NGC 104) with the Chandra X-ray Observatory to study the population of compact binaries in the high stellar density core. A 70-kilosecond exposure of the cluster reveals a centrally concentrated population of faint (
L
x
∼ 10
30−33
ergs per second) x-ray sources, with at least 108 located within the central 2′ × 2.5′ and ≳ half with
L
x
≲ 10
30.5
ergs per second. All 15 millisecond pulsars (MSPs) recently located precisely by radio observations are identified, though 2 are unresolved by Chandra. The x-ray spectral and temporal characteristics, as well as initial optical identifications with the Hubble Space Telescope, suggest that ≳50 percent are MSPs, about 30 percent are accreting white dwarfs, about 15 percent are main-sequence binaries in flare outbursts, and only two to three are quiescent low-mass x-ray binaries containing neutron stars, the conventional progenitors of MSPs. An upper limit of about 470 times the mass of the sun is derived for the mass of an accreting central black hole in the cluster. These observations provide the first x-ray “color-magnitude” diagram for a globular cluster and census of its compact object and binary population.
Reciprocal Regulation Between
TOC1
and
LHY
/
CCA1
Within the
Arabidopsis
Circadian Clock
Authors: Alabadı́ David , Oyama Tokitaka , Yanovsky Marcelo J. , Harmon Franklin G. , Más Paloma , Kay Steve A.
Published: July 2002

The interactive regulation between clock genes is central for oscillator function. Here, we show interactions between the
Arabidopsis
clock genes
LATE ELONGATED HYPOCOTYL
(
LHY
),
CIRCADIAN CLOCK ASSOCIATED 1
(
CCA1
), and
TIMING OF CAB EXPRESSION 1
(
TOC1
). The MYB transcription factors LHY and CCA1 negatively regulate
TOC1
expression. We show that both proteins bind to a region in the
TOC1
promoter that is critical for its clock regulation. Conversely, TOC1 appears to participate in the positive regulation of
LHY
and
CCA1
expression. Our results indicate that these interactions form a loop critical for clock function in
Arabidopsis
.
Methane-Consuming Archaea Revealed by Directly Coupled Isotopic and Phylogenetic Analysis
Authors: Orphan Victoria J. , House Christopher H. , Hinrichs Kai-Uwe , McKeegan Kevin D. , DeLong Edward F.
Published: July 2002

Microorganisms living in anoxic marine sediments consume more than 80% of the methane produced in the world's oceans. In addition to single-species aggregates, consortia of metabolically interdependent bacteria and archaea are found in methane-rich sediments. A combination of fluorescence in situ hybridization and secondary ion mass spectrometry shows that cells belonging to one specific archaeal group associated with the
Methanosarcinales
were all highly depleted in
13
C (to values of –96‰). This depletion indicates assimilation of isotopically light methane into specific archaeal cells. Additional microbial species apparently use other carbon sources, as indicated by significantly higher
13
C/
12
C ratios in their cell carbon. Our results demonstrate the feasibility of simultaneous determination of the identity and the metabolic activity of naturally occurring microorganisms.
Spike Transmission and Synchrony Detection in Networks of GABAergic Interneurons
Authors: Galarreta Mario , Hestrin Shaul
Published: July 2002

The temporal pattern and relative timing of action potentials among neocortical neurons may carry important information. However, how cortical circuits detect or generate coherent activity remains unclear. Using paired recordings in rat neocortical slices, we found that the firing of fast-spiking cells can reflect the spiking pattern of single-axon pyramidal inputs. Moreover, this property allowed groups of fast-spiking cells interconnected by electrical and γ-aminobutyric acid (GABA)–releasing (GABAergic) synapses to detect the relative timing of their excitatory inputs. These results indicate that networks of fast-spiking cells may play a role in the detection and promotion of synchronous activity within the neocortex.
Mechanisms of Evolution in
Rickettsia conorii
and
R. prowazekii
Authors: Ogata Hiroyuki , Audic Stéphane , Renesto-Audiffren Patricia , Fournier Pierre-Edouard , Barbe Valérie , Samson Delphine , Roux Véronique , Cossart Pascale , Weissenbach Jean , Claverie Jean-Michel , Raoult Didier
Published: July 2002

Rickettsia conorii
is an obligate intracellular bacterium that causes Mediterranean spotted fever in humans. We determined the 1,268,755-nucleotide complete genome sequence of
R. conorii
, containing 1374 open reading frames. This genome exhibits 804 of the 834 genes of the previously determined
R. prowazekii
genome plus 552 supplementary open reading frames and a 10-fold increase in the number of repetitive elements. Despite these differences, the two genomes exhibit a nearly perfect colinearity that allowed the clear identification of different stages of gene alterations with gene remnants and 37 genes split in 105 fragments, of which 59 are transcribed. A 38-kilobase sequence inversion was dated shortly after the divergence of the genus.
Common and Contrasting Themes of Plant and Animal Diseases
Authors: Staskawicz Brian J. , Mudgett Mary Beth , Dangl Jeffrey L. , Galan Jorge E.
Published: July 2002

Recent studies in bacterial pathogenesis reveal common and contrasting mechanisms of pathogen virulence and host resistance in plant and animal diseases. This review presents recent developments in the study of plant and animal pathogenesis, with respect to bacterial colonization and the delivery of effector proteins to the host. Furthermore, host defense responses in both plants and animals are discussed in relation to mechanisms of pathogen recognition and defense signaling. Future studies will greatly add to our understanding of the molecular events defining host-pathogen interactions.
Integration Between the Epibranchial Placodes and the Hindbrain
Authors: Begbie Jo , Graham Anthony
Published: July 2002

Developmental integration results from coordination among components of different embryonic fields to realize the later anatomical and functional relationships. We demonstrate that in the chick head, integration between the epibranchial placodes and the hindbrain is achieved as the neuroglial hindbrain crest cells guide the epibranchial neuronal cells inward to establish their central connections. This work defines a role for the neuroglial hindbrain crest in organizing the afferent innervation of the hindbrain.
Regulation of Transcriptional Activation Domain Function by Ubiquitin
Authors: Salghetti Simone E. , Caudy Amy A. , Chenoweth Joshua G. , Tansey William P.
Published: July 2002

The ability of transcriptional activation domains (TADs) to signal ubiquitin-mediated proteolysis suggests an involvement of the ubiquitin-proteasome pathway in transcription. To probe this involvement, we asked how ubiquitylation regulates the activity of a transcription factor containing the VP16 TAD. We show that the VP16 TAD signals ubiquitylation through the Met30 ubiquitin-ligase and that Met30 is also required for the VP16 TAD to activate transcription. The requirement for Met30 in transcription is circumvented by fusion of ubiquitin to the VP16 activator, demonstrating that activator ubiquitylation is essential for transcriptional activation. We propose that ubiquitylation regulates TAD function by serving as a dual signal for activation and activator destruction.
Immunocyte Ca
2+
Influx System Mediated by LTRPC2
Authors: Sano Yorikata , Inamura Kohei , Miyake Akira , Mochizuki Shinobu , Yokoi Hiromichi , Matsushime Hitoshi , Furuichi Kiyoshi
Published: July 2002

We characterized an activation mechanism of the human LTRPC2 protein, a member of the transient receptor potential family of ion channels, and demonstrated that LTRPC2 mediates Ca
2+
influx into immunocytes. Intracellular pyrimidine nucleotides, adenosine 5′-diphosphoribose (ADPR), and nicotinamide adenine dinucleotide (NAD), directly activated LTRPC2, which functioned as a Ca
2+
-permeable nonselective cation channel and enabled Ca
2+
influx into cells. This activation was suppressed by intracellular adenosine triphosphate. These results reveal that ADPR and NAD act as intracellular messengers and may have an important role in Ca
2+
influx by activating LTRPC2 in immunocytes.
Conversion of a Peroxiredoxin into a Disulfide Reductase by a Triplet Repeat Expansion
Authors: Ritz Daniel , Lim Jackie , Reynolds C. Michael , Poole Leslie B. , Beckwith Jon
Published: July 2002

Pathways for the reduction of protein disulfide bonds are found in all organisms and are required for the reductive recycling of certain enzymes including the essential protein ribonucleotide reductase. An
Escherichia coli
strain that lacks both thioredoxin reductase and glutathione reductase grows extremely poorly. Here, we show that a mutation occurring at high frequencies in the gene
ahpC
, encoding a peroxiredoxin, restores normal growth to this strain. This mutation is the result of a reversible expansion of a triplet nucleotide repeat sequence, leading to the addition of one amino acid that converts the AhpC protein from a peroxidase to a disulfide reductase. The ready mutational interconversion between the two activities could provide an evolutionary advantage to
E. coli
.
Magnetic Field-Tuned Quantum Criticality in the Metallic Ruthenate Sr
3
Ru
2
O
7
Authors: Grigera S. A. , Perry R. S. , Schofield A. J. , Chiao M. , Julian S. R. , Lonzarich G. G. , Ikeda S. I. , Maeno Y. , Millis A. J. , Mackenzie A. P.
Published: July 2002

The concept of quantum criticality is proving to be central to attempts to understand the physics of strongly correlated electrons. Here, we argue that observations on the itinerant metamagnet Sr
3
Ru
2
O
7
represent good evidence for a new class of quantum critical point, arising when the critical end point terminating a line of first-order transitions is depressed toward zero temperature. This is of interest both in its own right and because of the convenience of having a quantum critical point for which the tuning parameter is the magnetic field. The relationship between the resultant critical fluctuations and novel behavior very near the critical field is discussed.
Sea Level Rise During Past 40 Years Determined from Satellite and in Situ Observations
Authors: Cabanes Cecile , Cazenave Anny , Le Provost Christian
Published: July 2002

The 3.2 ± 0.2 millimeter per year global mean sea level rise observed by the Topex/Poseidon satellite over 1993–98 is fully explained by thermal expansion of the oceans. For the period 1955–96, sea level rise derived from tide gauge data agrees well with thermal expansion computed at the same locations. However, we find that subsampling the thermosteric sea level at usual tide gauge positions leads to a thermosteric sea level rise twice as large as the “true” global mean. As a possible consequence, the 20th century sea level rise estimated from tide gauge records may have been overestimated.
Transitions in Distinct Histone H3 Methylation Patterns at the Heterochromatin Domain Boundaries
Authors: Noma Ken-ichi , Allis C. David , Grewal Shiv I. S.
Published: July 2002

Eukaryotic genomes are organized into discrete structural and functional chromatin domains. Here, we show that distinct site-specific histone H3 methylation patterns define euchromatic and heterochromatic chromosomal domains within a 47-kilobase region of the mating-type locus in fission yeast. H3 methylated at lysine 9 (H3 Lys
9
), and its interacting Swi6 protein, are strictly localized to a 20-kilobase silent heterochromatic interval. In contrast, H3 methylated at lysine 4 (H3 Lys
4
) is specific to the surrounding euchromatic regions. Two inverted repeats flanking the silent interval serve as boundary elements to mark the borders between heterochromatin and euchromatin. Deletions of these boundary elements lead to spreading of H3 Lys
9
methylation and Swi6 into neighboring sequences. Furthermore, the H3 Lys
9
methylation and corresponding heterochromatin-associated complexes prevent H3 Lys
4
methylation in the silent domain.
Field-Induced Superconductivity in a Spin-Ladder Cuprate
Authors: Schön J. H. , Dorget M. , Beuran F. C. , Xu X. Z. , Arushanov E. , Laguës M. , Cavellin C. Deville
Published: July 2002

We report on the modulation of the transport properties of thin films, grown by molecular beam epitaxy, of the spin-ladder compound [CaCu
2
O
3
]
4
, using the field effect in a gated structure. At high hole-doping levels, superconductivity is induced in the nominally insulating ladder material without the use of high-pressure or chemical substitution. The observation of superconductivity is in agreement with the theoretical prediction that holes doped into spin ladders could pair and possibly superconduct.
Induction of Pancreatic Differentiation by Signals from Blood Vessels
Authors: Lammert Eckhard , Cleaver Ondine , Melton Douglas
Published: July 2002

Blood vessels supply developing organs with metabolic sustenance. Here, we demonstrate a role for blood vessels as a source of developmental signals during pancreatic organogenesis. In vitro experiments with embryonic mouse tissues demonstrate that blood vessel endothelium induces insulin expression in isolated endoderm. Removal of the dorsal aorta in
Xenopus laevis
embryos results in the failure of insulin expression in vivo. Furthermore, using transgenic mice, we show that ectopic vascularization in the posterior foregut leads to ectopic insulin expression and islet hyperplasia. These results indicate that vessels not only provide metabolic sustenance, but also provide inductive signals for organ development.
High-Temperature Superconductivity in Lattice-Expanded C
60
Authors: Schön J. H. , Kloc Ch. , Batlogg B.
Published: July 2002

C
60
single crystals have been intercalated with CHCl
3
and CHBr
3
in order to expand the lattice. High densities of electrons and holes have been induced by gate doping in a field-effect transistor geometry. At low temperatures, the material turns superconducting with a maximum transition temperature of 117 K in hole-doped C
60
/CHBr
3
. The increasing spacing between the C
60
molecules follows the general trend of alkali metal–doped C
60
and suggests routes to even higher transition temperatures.
Cooperation and Competition Between Relatives
Authors: West Stuart A. , Pen Ido , Griffin Ashleigh S.
Published: July 2002

Individuals are predicted to behave more altruistically and less competitively toward their relatives, because they share a relatively high proportion of their genes (e.g., one-half for siblings and one-eighth for cousins). Consequently, by helping a relative reproduce, an individual passes its genes to the next generation, increasing their Darwinian fitness. This idea, termed kin selection, has been applied to a wide range of phenomena in systems ranging from replicating molecules to humans. Nevertheless, competition between relatives can reduce, and even totally negate, the kin-selected benefits of altruism toward relatives. Recent theoretical work has clarified the processes and selective forces underlying this effect and has demonstrated the generality of the effect of competition between relatives.
Protein Structure Prediction and Structural Genomics
Authors: Baker David , Sali Andrej
Published: July 2002

Genome sequencing projects are producing linear amino acid sequences, but full understanding of the biological role of these proteins will require knowledge of their structure and function. Although experimental structure determination methods are providing high-resolution structure information about a subset of the proteins, computational structure prediction methods will provide valuable information for the large fraction of sequences whose structures will not be determined experimentally. The first class of protein structure prediction methods, including threading and comparative modeling, rely on detectable similarity spanning most of the modeled sequence and at least one known structure. The second class of methods, de novo or ab initio methods, predict the structure from sequence alone, without relying on similarity at the fold level between the modeled sequence and any of the known structures. In this Viewpoint, we begin by describing the essential features of the methods, the accuracy of the models, and their application to the prediction and understanding of protein function, both for single proteins and on the scale of whole genomes. We then discuss the important role that protein structure prediction methods play in the growing worldwide effort in structural genomics.
Dynamic Brain Sources of Visual Evoked Responses
Authors: Makeig S. , Westerfield M. , Jung T.-P. , Enghoff S. , Townsend J. , Courchesne E. , Sejnowski T. J.
Published: July 2002

It has been long debated whether averaged electrical responses recorded from the scalp result from stimulus-evoked brain events or stimulus-induced changes in ongoing brain dynamics. In a human visual selective attention task, we show that nontarget event-related potentials were mainly generated by partial stimulus-induced phase resetting of multiple electroencephalographic processes. Independent component analysis applied to the single-trial data identified at least eight classes of contributing components, including those producing central and lateral posterior alpha, left and right mu, and frontal midline theta rhythms. Scalp topographies of these components were consistent with their generation in compact cortical domains.
Optical Projection Tomography as a Tool for 3D Microscopy and Gene Expression Studies
Authors: Sharpe James , Ahlgren Ulf , Perry Paul , Hill Bill , Ross Allyson , Hecksher-Sørensen Jacob , Baldock Richard , Davidson Duncan
Published: July 2002

Current techniques for three-dimensional (3D) optical microscopy (deconvolution, confocal microscopy, and optical coherence tomography) generate 3D data by “optically sectioning” the specimen. This places severe constraints on the maximum thickness of a specimen that can be imaged. We have developed a microscopy technique that uses optical projection tomography (OPT) to produce high-resolution 3D images of both fluorescent and nonfluorescent biological specimens with a thickness of up to 15 millimeters. OPT microscopy allows the rapid mapping of the tissue distribution of RNA and protein expression in intact embryos or organ systems and can therefore be instrumental in studies of developmental biology or gene function.
The Role of Endosymbiotic
Wolbachia
Bacteria in the Pathogenesis of River Blindness
Authors: André Amélie v. Saint , Blackwell Nathan M. , Hall Laurie R. , Hoerauf Achim , Brattig Norbert W. , Volkmann Lars , Taylor Mark J. , Ford Louise , Hise Amy G. , Lass Jonathan H. , Diaconu Eugenia , Pearlman Eric
Published: July 2002

Parasitic filarial nematodes infect more than 200 million individuals worldwide, causing debilitating inflammatory diseases such as river blindness and lymphatic filariasis. Using a murine model for river blindness in which soluble extracts of filarial nematodes were injected into the corneal stroma, we demonstrated that the predominant inflammatory response in the cornea was due to species of endosymbiotic
Wolbachia
bacteria. In addition, the inflammatory response induced by these bacteria was dependent on expression of functional Toll-like receptor 4 (TLR4) on host cells.
RNA-Dependent RNA Polymerases, Viruses, and RNA Silencing
Authors: Ahlquist Paul
Published: July 2002

Most viruses have RNA genomes that are replicated and transcribed into messenger RNA by viral RNA–dependent RNA polymerases (RdRps), usually in concert with other viral and host factors. Many, if not most, eukaryotes also encode putative RdRps that have been implicated in sequence-specific, RNA-triggered gene silencing. Although the viral and cellular RdRps have no sequence homology, they share functional similarities such as copying messenger RNA templates and intercellular spread of the amplified sequences. Better understanding of viral and host RdRps will improve our ability to control viruses and to use RNA silencing and viruses as tools for research, biotechnology, and medicine.
Role of Yersinia Murine Toxin in Survival of
Yersinia pestis
in the Midgut of the Flea Vector
Authors: Hinnebusch B. Joseph , Rudolph Amy E. , Cherepanov Peter , Dixon Jack E. , Schwan Tom G. , Forsberg Åke
Published: July 2002

Transmission by flea bite is a relatively recent adaptation that distinguishes
Yersinia pestis
, the plague bacillus, from closely related enteric bacteria. Here, a plasmid-encoded phospholipase D (PLD), previously characterized as Yersinia murine toxin (Ymt), was shown to be required for survival of
Y. pestis
in the midgut of its principal vector, the rat flea
Xenopsylla cheopis
. Intracellular PLD activity appeared to protect
Y. pestis
from a cytotoxic digestion product of blood plasma in the flea gut. By enabling colonization of the flea midgut, acquisition of this PLD may have precipitated the transition of
Y. pestis
to obligate arthropod-borne transmission.
A Cyclic Model of the Universe
Authors: Steinhardt Paul J. , Turok Neil
Published: July 2002

We propose a cosmological model in which the universe undergoes an endless sequence of cosmic epochs that begin with a “bang” and end in a “crunch.” Temperature and density at the transition remain finite. Instead of having an inflationary epoch, each cycle includes a period of slow accelerated expansion (as recently observed) followed by contraction that produces the homogeneity, flatness, and energy needed to begin the next cycle.
The Many Selves of Social Insects
Authors: Queller David C. , Strassmann Joan E.
Published: July 2002

Social insects show multiple levels of self identity. Most individuals are sterile workers who selflessly labor for their colony, which is often viewed as a superorganism. The superorganism protects itself with colony recognition systems based on learned odors, typically cuticular hydrocarbons. Transfer of these odors within the colony obscures separate clan identities. Residual individual interests do appear to cause conflicts within colonies over sex ratio, male production, caste, and reproductive dominance. However, genomic imprinting theory predicts that the individual's maternal and paternal genes will evolve separate infraorganismal identities, perhaps leaving virtually no coherent individual identity.
Control of T Cell Function by Positive and Negative Regulators
Authors: Singer Andrew L. , Koretzky Gary A.
Published: July 2002

T cells are an essential element of the body's immune system. Engagement of the T cell receptor is responsible for initiating the signaling events that can activate, inactivate, or eliminate T cells, depending on the magnitude and duration of the signal. Control of T cell signaling occurs through both positive and negative regulation, as well as through the actions of molecular scaffolds that contribute to the formation of signaling complexes. The T Cell Signal Transduction Pathway at the STKE Connections Maps highlights the molecular components that are responsible for T cell activation. Understanding the mechanisms that regulate T cell responsiveness will aid in the development of therapeutic agents to treat infection, cancer, and autoimmune disease and immune deficiency.
Extra Dimensions and Warped Geometries
Authors: Randall Lisa
Published: July 2002

The field of extra dimensions, as well as the hypothesized sizes of extra dimensions, have grown by leaps and bounds over the past few years. I summarize the new results and the reasons for the recent activity in this field. These include the observations that extra dimensions can be macroscopic or even infinite in size. Another new development is the application of extra dimensions to the determination of particle physics parameters and properties.
Dynamical Instabilities and the Formation of Extrasolar Planetary Systems
Authors: Rasio Frederic A. , Ford Eric B.
Published: July 2002

The existence of a dominant massive planet, Jupiter, in our solar system, although perhaps essential for long-term dynamical stability and the development of life, may not be typical of planetary systems that form around other stars. In a system containing two Jupiter-like planets, the possibility exists that a dynamical instability will develop. Computer simulations suggest that in many cases this instability leads to the ejection of one planet while the other is left in a smaller, eccentric orbit. In extreme cases, the eccentric orbit has a small enough periastron distance that it may circularize at an orbital period as short as a few days through tidal dissipation. This may explain the recently detected Jupiter-mass planets in very tight circular orbits and wider eccentric orbits around nearby stars.
Liver Failure and Defective Hepatocyte Regeneration in Interleukin-6-Deficient Mice
Authors: Cressman Drew E. , Greenbaum Linda E. , DeAngelis Robert A. , Ciliberto Gennaro , Furth Emma E. , Poli Valeria , Taub Rebecca
Published: July 2002

Liver regeneration stimulated by a loss of liver mass leads to hepatocyte and nonparenchymal cell proliferation and rapid restoration of liver parenchyma. Mice with targeted disruption of the interleukin-6 (IL-6) gene had impaired liver regeneration characterized by liver necrosis and failure. There was a blunted DNA synthetic response in hepatocytes of these mice but not in nonparenchymal liver cells. Furthermore, there were discrete G
1
phase (prereplicative stage in the cell cycle) abnormalities including absence of STAT3 (signal transducer and activator of transcription protein 3) activation and depressed AP-1, Myc, and cyclin D1 expression. Treatment of IL-6-deficient mice with a single preoperative dose of IL-6 returned STAT3 binding, gene expression, and hepatocyte proliferation to near normal and prevented liver damage, establishing that IL-6 is a critical component of the regenerative response.
Control of
C. elegans
Larval Development by Neuronal Expression of a TGF-β Homolog
Authors: Ren Peifeng , Lim Chang-Su , Johnsen Robert , Albert Patrice S. , Pilgrim David , Riddle Donald L.
Published: July 2002

The
Caenorhabditis elegans
dauer larva is specialized for dispersal without growth and is formed under conditions of overcrowding and limited food. The
daf-7
gene, required for transducing environmental cues that support continuous development with plentiful food, encodes a transforming growth factor-β (TGF-β) superfamily member. A
daf-7
reporter construct is expressed in the ASI chemosensory neurons. Dauer-inducing pheromone inhibits
daf-7
expression and promotes dauer formation, whereas food reactivates
daf-7
expression and promotes recovery from the dauer state. When the food/pheromone ratio is high, the level of
daf-7
mRNA peaks during the L1 larval stage, when commitment to non-dauer development is made.
Duma Holds Down Science Budget
Authors: Allakhverdov Andrey , Pokrovsky Vladimir
Published: July 2002

Moscow—Russian science is scheduled for a big increase as legislators debate the country's 1997 budget. But the bad news is that it's not as much as government officials have promised, and it won't be nearly enough to repair the damage of the past several years.
Improbable Particles—or Artifacts?
Authors: Watson Andrew
Published: July 2002

Over the past year, one of the four huge detectors on the Large Electron-Positron Collider at CERN, the European Center for Particle Physics, has picked up 18 unusual events. Marked by debris that forms four jets and has an unusual pattern of masses, the events don't fit into any known physics, but they are so tantalizing that, so far, physicists can't write them off.
Researchers Construct Cell Look-Alikes
Authors: Service Robert F.
Published: July 2002

Materials scientists have taken another step toward mimicking biological structures. They have assembled groups of lipid molecules into structures resembling cells, with an outer membrane encasing a series of vesicles. The artificial cells may boost efforts to use lipid spheres for delivering drugs to tumors and other tissues: By slowing the release of the drugs, the double membranes could lengthen the time between doses.
Linkage of G Protein-Coupled Receptors to the MAPK Signaling Pathway Through PI 3-Kinase γ
Authors: Lopez-Ilasaca Marco , Crespo Piero , Pellici P. Giuseppe , Gutkind J. Silvio , Wetzker Reinhard
Published: July 2002

The tyrosine kinase class of receptors induces mitogen-activated protein kinase (MAPK) activation through the sequential interaction of the signaling proteins Grb2, Sos, Ras, Raf, and MEK. Receptors coupled to heterotrimeric guanine triphosphate-binding protein (G protein) stimulate MAPK through G
β
γ
subunits, but the subsequent intervening molecules are still poorly defined. Overexpression of phosphoinositide 3-kinase γ (PI3Kγ) in COS-7 cells activated MAPK in a G
β
γ
-dependent fashion, and expression of a catalytically inactive mutant of PI3Kγ abolished the stimulation of MAPK by G
β
γ
or in response to stimulation of muscarinic (m2) G protein-coupled receptors. Signaling from PI3Kγ to MAPK appears to require a tyrosine kinase, Shc, Grb2, Sos, Ras, and Raf. These findings indicate that PI3Kγ mediates G
β
γ
-dependent regulation of the MAPK signaling pathway.
Leaders Protest Cuts in Science Support
Authors: Koenig Robert
Published: July 2002

BERLIN
—In a highly unusual appeal, leaders of five of Germany's premier scientific organizations last week issued a dire public statement about the future of German research. They warned that their nation—which has produced some of the century's greatest scientists—is in danger of squandering golden opportunities for scientific achievement unless government and industry “significantly increase” their investments in research and work to make higher education more competitive.
Photons Add Up to Better Microscopy
Authors: Pennisi Elizabeth
Published: July 2002

A new microscopy technique may open new vistas for researchers who want to peer into living cells. On
page 530
, a research team from Cornell University describes how they used the additive energies of multiple photons to excite fluorescence from molecules that previously couldn't be observed with damaging or killing cells. In the current work, the researchers measured serotonin concentrations in living cells, but the technique should have a much broader application than that.
More Powerful Pulses Please and Puzzle
Authors: Normile Dennis
Published: July 2002

OSAKA, JAPAN
—New results from Japan on boosting electrons to record energy levels could hasten the arrival of a new generation of compact particle accelerators powered by laser pulses—if they hold up. The problem is that theorists so far haven't been able to explain theachievement.
Archaeologists Take to the Streets
Authors: Balter Michael
Published: July 2002

PARIS
—A dispute sparked when construction work threatened an archaeological site in the southern French city of Rodez has become a rallying cause for French archaeologists. Last month, many researchers staged a week-long strike which culminated last week in a demonstration that brought more than 1000 people onto the streets of Paris. Their goal: to persuade the government to pass new laws to protect vulnerable historic sites.
Declining Enrollments, Funds Threaten Small Departments
Authors: Williams Nigel
Published: July 2002

LONDON
—The chill wind of competition now blowing through Britain's higher education system is proving too frosty for some of the smaller university departments of physics and chemistry. Declining enrollment in science courses and a new formula announced last month for distributing infrastructure funds over the next 4 years have led three universities to shut down some undergraduate physics and chemistry courses, while whole departments may be closed at two other institutions.
Peña Wins Reprieve on Realignment
Authors: Lawler Andrew
Published: July 2002

Energy Secretary nominee Federico Peña appears headed for both confirmation in the job and at least a brief honeymoon with Congress. The clearest sign of that is a decision by Senator Pete Domenici (R-NM) to delay his plan to reorganize and downsize the Department of Energy until Peña has had a chance to reform the troubled agency.
First Nematode-Resistance Gene Found
Authors: Moffat Anne Simon
Published: July 2002

Plant biologists have had little success in breeding commercial varieties of nematode-resistant crops. But researchers from three European labs report in this issue (
p 832
) that they have identified the first gene for nematode resistance, which bears some resemblance to previously discovered resistance genes for bacteria and other pathogens. The finding may allow researchers to genetically engineer the trait into plants.
Biotechnology: Genomics's Odd Couple
Authors: Marshall Eliot
Published: July 2002

Fundamental tensions over control of data have severely strained relations between The Institute for Genomic Research's J. Craig Venter and Human Genome Sciences Inc.'s William Haseltine.
Somatic Frameshift Mutations in the
BAX
Gene in Colon Cancers of the Microsatellite Mutator Phenotype
Authors: Rampino Nicholas , Yamamoto Hiroyuki , Ionov Yurij , Li Yan , Sawai Hisako , Reed John C. , Perucho Manuel
Published: July 2002

Cancers of the microsatellite mutator phenotype (MMP) show exaggerated genomic instability at simple repeat sequences. More than 50 percent (21 out of 41) of human MMP
+
colon adenocarcinomas examined were found to have frameshift mutations in a tract of eight deoxyguanosines [(G)
8
] within
BAX
, a gene that promotes apoptosis. These mutations were absent in MMP
−
tumors and were significantly less frequent in (G)
8
repeats from other genes. Frameshift mutations were present in both
BAX
alleles in some MMP
+
colon tumor cell lines and in primary tumors. These results suggest that inactivating
BAX
mutations are selected for during the progression of colorectal MMP
+
tumors and that the wild-type
BAX
gene plays a suppressor role in a p53-independent pathway for colorectal carcinogenesis.
A Protein-Counting Mechanism for Telomere Length Regulation in Yeast
Authors: Marcand Stéphane , Gilson Eric , Shore David
Published: July 2002

In the yeast
Saccharomyces cerevisiae
, telomere elongation is negatively regulated by the telomere repeat-binding protein Rap1p, such that a narrow length distribution of telomere repeat tracts is observed. This length regulation was shown to function independently of the orientation of the telomere repeats. The number of repeats at an individual telomere was reduced when hybrid proteins containing the Rap1p carboxyl terminus were targeted there by a heterologous DNA-binding domain. The extent of this telomere tract shortening was proportional to the number of targeted molecules, consistent with a feedback mechanism of telomere length regulation that can discriminate the precise number of Rap1p molecules bound to the chromosome end.
Defective Transcription-Coupled Repair of Oxidative Base Damage in Cockayne Syndrome Patients from XP Group G
Authors: Cooper Priscilla K. , Nouspikel Thierry , Clarkson Stuart G. , Leadon Steven A.
Published: July 2002

In normal human cells, damage due to ultraviolet light is preferentially removed from active genes by nucleotide excision repair (NER) in a transcription-coupled repair (TCR) process that requires the gene products defective in Cockayne syndrome (CS). Oxidative damage, including thymine glycols, is shown to be removed by TCR in cells from normal individuals and from xeroderma pigmentosum (XP)-A, XP-F, and XP-G patients who have NER defects but not from XP-G patients who have severe CS. Thus, TCR of oxidative damage requires an XPG function distinct from its NER endonuclease activity. These results raise the possibility that defective TCR of oxidative damage contributes to the developmental defects associated with CS.
Civilian Lab Grabs NIF's Coattails
Authors: Lawler Andrew
Published: July 2002

BERKELEY, CALIFORNIA
—In a major break with the past, Lawrence Berkeley National Laboratory is touting the opportunity for collaboration with Lawrence Livermore National Laboratory in its campaign to secure funds for a $150 million heavy-ion accelerator that will complement the inertial-confinement fusion program at NIF.
Whirling Neutron Stars May Brake and Accelerate
Authors: Stokstad Erik
Published: July 2002

SEATTLE
—Astronomers studying bursts of x-rays from rapidly spinning neutron stars may have seen the thin atmosphere of one superdense object brake and accelerate like a spinning figure skater, all in the space of a few seconds. The finding, from NASA's X-ray Timing Explorer satellite, was presented at the annual meeting of the American Association for the Advancement of Science here.

See last week's issue (
Science
, 21 February, p.
1061
)for coverage of early sessions on
global R&D funding
and
submarine vents
.
Feds Probe Causes of Academic Stress
Authors: Mervis Jeffrey
Published: July 2002

The White House has launched a 6-month review of federal policies affecting universities in the hope of improving the health of the government-university research nexus. At a roundtable held at the National Academy of Sciences in Washington, D.C., last week, participants expressed concern about sudden shifts in federal funding, inadequate reimbursement for the cost of supporting research on campus, and insufficient attention to education and training.
Parasites Shed Light on Cellular Evolution
Authors: Vogel Gretchen
Published: July 2002

It's been well established that the energy-producing mitochondria and photosynthesizing chloroplasts of today's cells originated from bacteria that took up residence in some ancestral cell. But new studies indicate that such organelles can also be acquired when a complex cell engulfs another complex cell. On
page 1485
, researchers report that single-cell parasites, including
Toxoplasma
, which causes infections in AIDS patients, and malaria-causing
Plasmodium
, apparently got their chloroplast-like organelles when an ancestor engulfed an algal cell. Not only do the new findings shed light on cellular evolution, but the plastids found in the parasites may be new targets for drug therapies.
Structure of a Protein Photocycle Intermediate by Millisecond Time-Resolved Crystallography
Authors: Genick Ulrich K. , Borgstahl Gloria E. O. , Ng Kingman , Ren Zhong , Pradervand Claude , Burke Patrick M. , Šrajer Vukica , Teng Tsu-Yi , Schildkamp Wilfried , McRee Duncan E. , Moffat Keith , Getzoff Elizabeth D.
Published: July 2002

The blue-light photoreceptor photoactive yellow protein (PYP) undergoes a self-contained light cycle. The atomic structure of the bleached signaling intermediate in the light cycle of PYP was determined by millisecond time-resolved, multiwavelength Laue crystallography and simultaneous optical spectroscopy. Light-induced trans-to-cis isomerization of the 4-hydroxycinnamyl chromophore and coupled protein rearrangements produce a new set of active-site hydrogen bonds. An arginine gateway opens, allowing solvent exposure and protonation of the chromophore's phenolic oxygen. Resulting changes in shape, hydrogen bonding, and electrostatic potential at the protein surface form a likely basis for signal transduction. The structural results suggest a general framework for the interpretation of protein photocycles.
Sea-Floor Depth and the Lake Wobegon Effect
Authors: Stein Seth , Stein Carol A.
Published: July 2002

The ways in which actual measurements of sea-floor depth differ from average depths predicted by models of the solid Earth may provide useful information about how the planetary heat engine works. Actual depth is a function of plate tectonics and planetary heat flow. As S. Stein and C. Stein discuss in their Perspective, there is renewed interest in understanding these depth anomalies that is leading to improved models and extensive data sets.
Researchers Vie for Role in Nuclear-Waste Cleanup
Authors: Lawler Andrew
Published: July 2002

RICHLAND, WASHINGTON
—An effort to entice researchers to lend a hand in long-range solutions to nuclear-weapons cleanup started with a $50 million a year bang. But a new report from the National Research Council and a pending 10-year plan from the Department of Energy point out serious obstacles to bringing researchers into the cleanup effort.
A New Voice for European Scientists?
Authors: Hellemans Alexander
Published: July 2002

STRASBOURG, FRANCE
—About a year ago, a dozen European scientists identified something they saw as missing from the European research scene: an organization to act as a voice for working researchers across the continent. Last weekend at a constituent assembly of 200 “founding members” here, that vacuum was transformed into “Euroscience,” an association of scientists and citizens concerned about science and technology, modeled on the American Association for the Advancement of Science.
U.S. Antarctic Panel Makes Case for Replacement Station
Authors: Mervis Jeffrey
Published: July 2002

A blue-ribbon panel has recommended that the National Science Foundation proceed with plans to build a new U.S. research station at the South Pole to replace its aging facility there. But the panel also says the new station should be a slimmed-down version of a facility proposed 3 years ago.
ATCC Plant-Virus Collection Threatened
Authors: Moffat Anne Simon
Published: July 2002

Plant pathologists fear that a valuable collection of plant viruses and viroids may be threatened. For financial reasons, the American Type Culture Collection (ATCC), a vast library of microbial cultures that is a vital resource for researchers around the world, has decided, for now, not to build a greenhouse at its new facility in Manassas, Virginia, and has also dismissed the curator of the plant-virus collection. ATCC officials say they want to protect the collection, but even they concede that it might be in jeopardy.