bluuebunny/crossref_metadata_2025 huggingface dataset:
Regulation of Differentiation to the Infective Stage of the Protozoan Parasite
Leishmania major
by Tetrahydrobiopterin
Authors: Cunningham Mark L. , Titus Richard G. , Turco Salvatore J. , Beverley Stephen M.
Published: July 2002

A critical step in the infectious cycle of
Leishmania
is the differentiation of parasites within the sand fly vector to the highly infective metacyclic promastigote stage. Here, we establish tetrahydrobiopterin (H
4
B) levels as an important factor controlling the extent of metacyclogenesis. H
4
B levels decline substantially during normal development, and genetic or nutritional manipulations showed that low H
4
B caused elevated metacyclogenesis. Mutants lacking pteridine reductase 1 (PTR1) had low levels of H
4
B, remained infectious to mice, and induced larger cutaneous lesions (hypervirulence). Thus, the control of pteridine metabolism has relevance to the mechanism of
Leishmania
differentiation and the limitation of virulence during evolution.
Squeezed States in a Bose-Einstein Condensate
Authors: Orzel C. , Tuchman A. K. , Fenselau M. L. , Yasuda M. , Kasevich M. A.
Published: July 2002

We report manipulation of the atom number statistics associated with Bose-Einstein condensed atoms confined in an array of weakly linked mesoscopic traps. We used the interference of atoms released from the traps as a sensitive probe of these statistics. By controlling relative strengths of the tunneling rate between traps and atom-atom interactions within each trap, we observed trap states characterized by sub-Poissonian number fluctuations and adiabatic transitions between these number-squeezed states and coherent states of the atom field. The quantum states produced in this work may enable substantial gains in sensitivity for atom interference–based instruments as well as fundamental studies of quantum phase transitions.
Variation of Crystal Dissolution Rate Based on a Dissolution Stepwave Model
Authors: Lasaga Antonio C. , Luttge Andreas
Published: July 2002

A formulation based on defect-generated dissolution stepwaves of the variation of dissolution rate with the degree of undersaturation is validated by near-atomic-scale observations of surfaces, Monte Carlo simulations, and experimental bulk dissolution rates. The dissolution stepwaves emanating from etch pits provide a train of steps similar to those of a spiral but with different behavior. Their role in accounting for the bulk dissolution rate of crystals provides a conceptual framework for mineral dissolution far from equilibrium. Furthermore, the law extends research to conditions closer to equilibrium and predicts a nonlinear decrease in the rate of dissolution as equilibrium is approached, which has implications for understanding artificial and natural processes involving solid-fluid reactions.
Reversible Unfolding of Single RNA Molecules by Mechanical Force
Authors: Liphardt Jan , Onoa Bibiana , Smith Steven B. , Tinoco Ignacio , Bustamante Carlos
Published: July 2002

Here we use mechanical force to induce the unfolding and refolding of single RNA molecules: a simple RNA hairpin, a molecule containing a three-helix junction, and the P5abc domain of the
Tetrahymena thermophila
ribozyme. All three molecules (P5abc only in the absence of Mg
2+
) can be mechanically unfolded at equilibrium, and when kept at constant force within a critical force range, are bi-stable and hop between folded and unfolded states. We determine the force-dependent equilibrium constants for folding/unfolding these single RNA molecules and the positions of their transition states along the reaction coordinate.
Preferential Localization of Effector Memory Cells in Nonlymphoid Tissue
Authors: Masopust David , Vezys Vaiva , Marzo Amanda L. , Lefrançois Leo
Published: July 2002

Many intracellular pathogens infect a broad range of host tissues, but the importance of T cells for immunity in these sites is unclear because most of our understanding of antimicrobial T cell responses comes from analyses of lymphoid tissue. Here, we show that in response to viral or bacterial infection, antigen-specific CD8 T cells migrated to nonlymphoid tissues and were present as long-lived memory cells. Strikingly, CD8 memory T cells isolated from nonlymphoid tissues exhibited effector levels of lytic activity directly ex vivo, in contrast to their splenic counterparts. These results point to the existence of a population of extralymphoid effector memory T cells poised for immediate response to infection.
Explaining the Weddell Polynya--a Large Ocean Eddy Shed at Maud Rise
Authors: Holland D. M.
Published: July 2002

Satellite observations have shown the occasional occurrence of a large opening in the sea-ice cover of the Weddell Sea, Antarctica, a phenomenon known as the Weddell Polynya. The transient appearance, position, size, and shape of the polynya is explained here by a mechanism by which modest variations in the large-scale oceanic flow past the Maud Rise seamount cause a horizontal cyclonic eddy to be shed from its northeast flank. The shed eddy transmits a divergent Ekman stress into the sea ice, leading to a crescent-shaped opening in the pack. Atmospheric thermodynamical interaction further enhances the opening by inducing oceanic convection. A sea-ice–ocean computer model simulation vividly demonstrates how this mechanism fully accounts for the characteristics that mark Weddell Polynya events.
Molecular Mechanisms of the Biological Clock in Cultured Fibroblasts
Authors: Yagita Kazuhiro , Tamanini Filippo , van der Horst Gijsbertus T. J. , Okamura Hitoshi
Published: July 2002

In mammals, the central circadian pacemaker resides in the hypothalamic suprachiasmatic nucleus (SCN), but circadian oscillators also exist in peripheral tissues. Here, using wild-type and
cryptochrome
(
mCry
)–deficient cell lines derived from
mCry
mutant mice, we show that the peripheral oscillator in cultured fibroblasts is identical to the oscillator in the SCN in (i) temporal expression profiles of all known clock genes, (ii) the phase of the various mRNA rhythms (i.e., antiphase oscillation of
Bmal1
and
mPer
genes), (iii) the delay between maximum mRNA levels and appearance of nuclear mPER1 and mPER2 protein, (iv) the inability to produce oscillations in the absence of functional
mCry
genes, and (v) the control of period length by mCRY proteins.
Graded Materials for Resistance to Contact Deformation and Damage
Authors: Suresh S.
Published: July 2002

The mechanical response of materials with spatial gradients in composition and structure is of considerable interest in disciplines as diverse as tribology, geology, optoelectronics, biomechanics, fracture mechanics, and nanotechnology. The damage and failure resistance of surfaces to normal and sliding contact or impact can be changed substantially through such gradients. This review assesses the current understanding of the resistance of graded materials to contact deformation and damage, and outlines future research directions and possible applications for graded materials.
Climate-Driven Range Expansion and Morphological Evolution in a Marine Gastropod
Authors: Hellberg Michael E. , Balch Deborah P. , Roy Kaustuv
Published: July 2002

Little is known about the phenotypic consequences of global climate change, despite the excellent Pleistocene fossil record of many taxa. We used morphological measurements from extant and Pleistocene populations of a marine gastropod (
Acanthinucella spirata
) in conjunction with mitochondrial DNA sequence variation from living populations to determine how populations responded phenotypically to Pleistocene climatic changes. Northern populations show little sequence variation as compared to southern populations, a pattern consistent with a recent northward range expansion. These recently recolonized northern populations also contain shell morphologies that are absent in extant southern populations and throughout the Pleistocene fossil record. Thus, contrary to traditional expectations that morphological evolution should occur largely within Pleistocene refugia, our data show that geographical range shifts in response to climatic change can lead to significant morphological evolution.
The Foot-and-Mouth Epidemic in Great Britain: Pattern of Spread and Impact of Interventions
Authors: Ferguson Neil M. , Donnelly Christl A. , Anderson Roy M.
Published: July 2002

We present an analysis of the current foot-and-mouth disease epidemic in Great Britain over the first 2 months of the spread of the virus. The net transmission potential of the pathogen and the increasing impact of control measures are estimated over the course of the epidemic to date. These results are used to parameterize a mathematical model of disease transmission that captures the differing spatial contact patterns between farms before and after the imposition of movement restrictions. The model is used to make predictions of future incidence and to simulate the impact of additional control strategies. Hastening the slaughter of animals with suspected infection is predicted to slow the epidemic, but more drastic action, such as “ring” culling or vaccination around infection foci, is necessary for more rapid control. Culling is predicted to be more effective than vaccination.
Observation of Chaos-Assisted Tunneling Between Islands of Stability
Authors: Steck Daniel A. , Oskay Windell H. , Raizen Mark G.
Published: July 2002

We report the direct observation of quantum dynamical tunneling of atoms between separated momentum regions in phase space. We study how the tunneling oscillations are affected as a quantum symmetry is broken and as the initial atomic state is changed. We also provide evidence that the tunneling rate is greatly enhanced by the presence of chaos in the classical dynamics. This tunneling phenomenon represents a dramatic manifestation of underlying classical chaos in a quantum system.
Inhibition of the
B. subtilis
Regulatory Protein TRAP by the TRAP-Inhibitory Protein, AT
Authors: Valbuzzi Angela , Yanofsky Charles
Published: July 2002

An anti-TRAP (AT) protein, a factor of previously unknown function, conveys the metabolic signal that the cellular transfer RNA for tryptophan (tRNA
Trp
) is predominantly uncharged. Expression of the operon encoding AT is induced by uncharged tRNA
Trp
. AT associates with TRAP, the
trp
operon attenuation protein, and inhibits its binding to its target RNA sequences. This relieves TRAP-mediated transcription termination and translation inhibition, increasing the rate of tryptophan biosynthesis. AT binds to TRAP primarily when it is in the tryptophan-activated state. The 53-residue AT polypeptide is homologous to the zinc-binding domain of DnaJ. The mechanisms regulating tryptophan biosynthesis in
Bacillus subtilis
differ from those used by
Escherichia coli
.
Dynamic Disruptions in Nuclear Envelope Architecture and Integrity Induced by HIV-1 Vpr
Authors: de Noronha Carlos M. C. , Sherman Michael P. , Lin Harrison W. , Cavrois Marielle V. , Moir Robert D. , Goldman Robert D. , Greene Warner C.
Published: July 2002

Human immunodeficiency virus–1 (HIV-1) Vpr expression halts the proliferation of human cells at or near the G
2
cell-cycle checkpoint. The transition from G
2
to mitosis is normally controlled by changes in the state of phosphorylation and subcellular compartmentalization of key cell-cycle regulatory proteins. In studies of the intracellular trafficking of these regulators, we unexpectedly found that wild-type Vpr, but not Vpr mutants impaired for G
2
arrest, induced transient, localized herniations in the nuclear envelope (NE). These herniations were associated with defects in the nuclear lamina. Intermittently, these herniations ruptured, resulting in the mixing of nuclear and cytoplasmic components. These Vpr-induced NE changes probably contribute to the observed cell-cycle arrest.
Extension of Life-Span in
Caenorhabditis elegans
by a Diet Lacking Coenzyme Q
Authors: Larsen Pamela L. , Clarke Catherine F.
Published: July 2002

The isoprenylated benzoquinone coenzyme Q is a redox-active lipid essential for electron transport in aerobic respiration. Here, we show that withdrawal of coenzyme Q (Q) from the diet of wild-type nematodes extends adult life-span by ∼60%. The longevity of
clk-1
,
daf-2
,
daf-12
, and
daf-16
mutants is also extended by a Q-less diet. These results establish the importance of Q in life-span determination. The findings suggest that Q and the
daf-2
pathway intersect at the mitochondria and imply that a concerted production coupled with enhanced scavenging of reactive oxygen species contributes to the substantial life-span extension.
RGS-PX1, a GAP for Gα
s
and Sorting Nexin in Vesicular Trafficking
Authors: Zheng Bin , Ma Yong-Chao , Ostrom Rennolds S. , Lavoie Christine , Gill Gordon N. , Insel Paul A. , Huang Xin-Yun , Farquhar Marilyn G.
Published: July 2002

Heterotrimeric GTP–binding proteins (G proteins) control cellular functions by transducing signals from the outside to the inside of cells. Regulator of G protein signaling (RGS) proteins are key modulators of the amplitude and duration of G protein–mediated signaling through their ability to serve as guanosine triphosphatase–activating proteins (GAPs). We have identified RGS-PX1, a Gα
s
-specific GAP. The RGS domain of RGS-PX1 specifically interacted with Gα
s
, accelerated its GTP hydrolysis, and attenuated Gα
s
-mediated signaling. RGS-PX1 also contains a Phox (PX) domain that resembles those in sorting nexin (SNX) proteins. Expression of RGS-PX1 delayed lysosomal degradation of the EGF receptor. Because of its bifunctional role as both a GAP and a SNX, RGS-PX1 may link heterotrimeric G protein signaling and vesicular trafficking.
A Near-Earth Asteroid Population Estimate from the LINEAR Survey
Authors: Stuart Joseph Scott
Published: July 2002

I estimate the size and shape of the near-Earth asteroid (NEA) population using survey data from the Lincoln Near-Earth Asteroid Research (LINEAR) project, covering 375,000 square degrees of sky and including more than 1300 NEA detections. A simulation of detection probabilities for different values of orbital parameters and sizes combined with the detection statistics in a Bayesian framework provides a correction for observational bias and yields the NEA population distribution as a function of absolute magnitude, semi-major axis, eccentricity, and inclination. The NEA population is more highly inclined than previously estimated, and the total number of kilometer-sized NEAs is 1227
−90
+170
(1σ).
Biodegradable, Elastic Shape-Memory Polymers for Potential Biomedical Applications
Authors: Lendlein Andreas , Langer Robert
Published: July 2002

The introduction of biodegradable implant materials as well as minimally invasive surgical procedures in medicine has substantially improved health care within the past few decades. This report describes a group of degradable thermoplastic polymers that are able to change their shape after an increase in temperature. Their shape-memory capability enables bulky implants to be placed in the body through small incisions or to perform complex mechanical deformations automatically. A smart degradable suture was created to illustrate the potential of these shape-memory thermoplastics in biomedical applications.
KLF6
, a Candidate Tumor Suppressor Gene Mutated in Prostate Cancer
Authors: Narla Goutham , Heath Karen E. , Reeves Helen L. , Li Dan , Giono Luciana E. , Kimmelman Alec C. , Glucksman Marc J. , Narla Jyothsna , Eng Francis J. , Chan Andrew M. , Ferrari Anna C. , Martignetti John A. , Friedman Scott L.
Published: July 2002

Kruppel-like factor 6 (
KLF6
) is a zinc finger transcription factor of unknown function. Here, we show that the
KLF6
gene is mutated in a subset of human prostate cancer. Loss-of-heterozygosity analysis revealed that one
KLF6
allele is deleted in 77% (17 of 22) of primary prostate tumors. Sequence analysis of the retained
KLF6
allele revealed mutations in 71% of these tumors. Functional studies confirm that whereas wild-type KLF6 up-regulates p21 (WAF1/CIP1) in a p53-independent manner and significantly reduces cell proliferation, tumor-derived KLF6 mutants do not. Our data suggest that
KLF6
is a tumor suppressor gene involved in human prostate cancer.
Plant Biotechnology in China
Authors: Huang Jikun , Rozelle Scott , Pray Carl , Wang Qinfang
Published: July 2002

A survey of China's plant biotechnologists shows that China is developing the largest plant biotechnology capacity outside of North America. The list of genetically modified plant technologies in trials, including rice, wheat, potatoes, and peanuts, is impressive and differs from those being worked on in other countries. Poor farmers in China are cultivating more area of genetically modified plants than are small farmers in any other developing country. A survey of agricultural producers in China demonstrates that
Bacillus thuringiensis
cotton adoption increases production efficiency and improves farmer health.
The North Atlantic Spring Phytoplankton Bloom and Sverdrup's Critical Depth Hypothesis
Authors: Siegel D. A. , Doney S. C. , Yoder J. A.
Published: July 2002

More than 50 years ago, Harald Sverdrup developed a simple model for the necessary conditions leading to the spring bloom of phytoplankton. Although this model has been used extensively across a variety of aquatic ecosystems, its application requires knowledge of community compensation irradiance (
I
C
), the light level where photosynthetic and ecosystem community loss processes balance. However, reported
I
C
values have varied by an order of magnitude. Here,
I
C
estimates are determined using satellite and hydrographic data sets consistent with the assumptions in Sverdrup's 1953 critical depth hypothesis. Retrieved values of
I
C
are approximately uniform throughout much of the North Atlantic with a mean value of 1.3 mol photons meter
−2
day
−1
. These community-based
I
C
determinations are roughly twice typical values found for phytoplankton alone indicating that phytoplankton account for approximately one-half of community ecosystem losses. This work also suggests that important aspects of heterotrophic community dynamics can be assessed using satellite observations.
Functional Neuroanatomical Differences Between Adults and School-Age Children in the Processing of Single Words
Authors: Schlaggar Bradley L. , Brown Timothy T. , Lugar Heather M. , Visscher Kristina M. , Miezin Francis M. , Petersen Steven E.
Published: July 2002

A critical issue in developmental cognitive neuroscience is the extent to which the functional neuroanatomy underlying task performance differs in adults and children. Direct comparisons of brain activation in the left frontal and extrastriate cortex were made in adults and children (aged 7 to 10 years) performing single-word processing tasks with visual presentation; differences were found in circumscribed frontal and extrastriate regions. Conceivably, these differences could be attributable exclusively to performance discrepancies; alternatively, maturational differences in functional neuroanatomy could exist despite similar performance. Some of the brain regions examined showed differences attributable to age independent of performance, suggesting that maturation of the pattern of regional activations for these tasks is incomplete at age 10.
Pyrrolysine Encoded by UAG in Archaea: Charging of a UAG-Decoding Specialized tRNA
Authors: Srinivasan Gayathri , James Carey M. , Krzycki Joseph A.
Published: July 2002

Pyrrolysine is a lysine derivative encoded by the UAG codon in methylamine methyltransferase genes of
Methanosarcina barkeri
. Near a methyltransferase gene cluster is the
pylT
gene, which encodes an unusual transfer RNA (tRNA) with a CUA anticodon. The adjacent
pylS
gene encodes a class II aminoacyl-tRNA synthetase that charges the
pylT
-derived tRNA with lysine but is not closely related to known lysyl-tRNA synthetases. Homologs of
pylS
and
pylT
are found in a Gram-positive bacterium. Charging a tRNA
CUA
with lysine is a likely first step in translating UAG amber codons as pyrrolysine in certain methanogens. Our results indicate that pyrrolysine is the 22nd genetically encoded natural amino acid.
Breast-Implant Ruling Sends a Message
Authors: Kaiser Jocelyn
Published: July 2002

When a federal judge in Oregon ruled last month that evidence linking silicone breast implants to autoimmune disorders in about 70 women is too weak to be presented to a jury, he sent a shock through the legal profession. If the ruling holds up, legal experts say it will strike a blow to billions of dollars worth of implant lawsuits nationwide. Some scientists and lawyers also believe that the procedure the judge used to exclude the evidence may provide a model for other high-profile cases where scientific evidence is in dispute.
A New View of How Leg Muscles Operate on the Run
Authors: Pennisi Elizabeth
Published: July 2002

Leg muscles are generally viewed as motors, contracting and relaxing to drive legs up, forward, and down. But new results reported on
page 1113
challenge the long-standing assumption that muscles always do actual work, shortening against resistance to propel an animal forward. By directly monitoring a leg muscle in turkeys running on a treadmill, researchers have now found that the muscle hardly contracts at all, at least when the animals run on level ground. Instead, it shortens slightly before the foot is planted to exert the force needed to keep the tendon attaching the muscle to the heel stretched while the foot is on the ground, thus storing energy for the next stride. As a result, the muscle does very little work.
Gliding Mechanism in the Late Permian Reptile
Coelurosauravus
Authors: Frey Eberhard , Sues Hans-Dieter , Munk Wolfgang
Published: July 2002

A complete skeleton of the oldest known flying reptile,
Coelurosauravus jaekeli,
from the Upper Permian of Germany, and reexamination of other specimens demonstrate that this animal had a gliding apparatus unlike that of any other tetrapod. The lateral gliding membrane was supported by radially disposed, greatly elongated bony rods of dermal origin in the thoracolumbar region, rather than by internal skeletal elements such as ribs and limb bones. The rods are independent of the ribcage and arranged in distinct bundles to form a cambered wing.
A Cellular Cofactor for the Constitutive Transport Element of Type D Retrovirus
Authors: Tang Hengli , Gaietta Guido M. , Fischer Wolfgang H. , Ellisman Mark H. , Wong-Staal Flossie
Published: July 2002

A human nuclear protein that specifically interacts with the constitutive transport element (CTE) of simian retrovirus was identified as adenosine 5′-triphosphate–dependent RNA helicase A. This protein could bind to functional CTE but not to inactive CTE mutants. The interaction of helicase A with CTE was distinct from previously described helicase activity of this protein. Helicase A shuttled from the nucleus to the cytoplasm in the presence of a transcription inhibitor or in cells transiently overexpressing CTE-containing RNA. In vivo colocalization of helicase A and CTE was observed in experiments that combined in situ hybridization and immunostaining. These results suggest that helicase A plays a role in the nuclear export of CTE-containing RNA.
Simplification of DNA Topology Below Equilibrium Values by Type II Topoisomerases
Authors: Rybenkov Valentin V. , Ullsperger Christian , Vologodskii Alexander V. , Cozzarelli Nicholas R.
Published: July 2002

Type II DNA topoisomerases catalyze the interconversion of DNA topoisomers by transporting one DNA segment through another. The steady-state fraction of knotted or catenated DNA molecules produced by prokaryotic and eukaryotic type II topoisomerases was found to be as much as 80 times lower than at thermodynamic equilibrium. These enzymes also yielded a tighter distribution of linking number topoisomers than at equilibrium. Thus, topoisomerases do not merely catalyze passage of randomly juxtaposed DNA segments but control a global property of DNA, its topology. The results imply that type II topoisomerases use the energy of adenosine triphosphate hydrolysis to preferentially remove the topological links that provide barriers to DNA segregation.
Synthesis of Gallium Nitride Nanorods Through a Carbon Nanotube-Confined Reaction
Authors: Han Weiqiang , Fan Shoushan , Li Qunqing , Hu Yongdan
Published: July 2002

Gallium nitride nanorods were prepared through a carbon nanotube–confined reaction. Ga
2
O vapor was reacted with NH
3
gas in the presence of carbon nanotubes to form wurtzite gallium nitride nanorods. The nanorods have a diameter of 4 to 50 nanometers and a length of up to 25 micrometers. It is proposed that the carbon nanotube acts as a template to confine the reaction, which results in the gallium nitride nanorods having a diameter similar to that of the original nanotubes. The results suggest that it might be possible to synthesize other nitride nanorods through similar carbon nanotube–confined reactions.
A Metalloradical Mechanism for the Generation of Oxygen from Water in Photosynthesis
Authors: Hoganson Curtis W. , Babcock Gerald T.
Published: July 2002

In plants and algae, photosystem II uses light energy to oxidize water to oxygen at a metalloradical site that comprises a tetranuclear manganese cluster and a tyrosyl radical. A model is proposed whereby the tyrosyl radical functions by abstracting hydrogen atoms from substrate water bound as terminal ligands to two of the four manganese ions. Molecular oxygen is produced in the final step in which hydrogen atom transfer and oxygen-oxygen bond formation occur together in a concerted reaction. This mechanism establishes clear analogies between photosynthetic water oxidation and amino acid radical function in other enzymatic reactions.
Requirement for Macrophage Elastase for Cigarette Smoke-Induced Emphysema in Mice
Authors: Hautamaki R. Dean , Kobayashi Dale K. , Senior Robert M. , Shapiro Steven D.
Published: July 2002

To determine which proteinases are responsible for the lung destruction characteristic of pulmonary emphysema, macrophage elastase–deficient (MME
−/−
) mice were subjected to cigarette smoke. In contrast to wild-type mice, MME
−
/
−
mice did not have increased numbers of macrophages in their lungs and did not develop emphysema in response to long-term exposure to cigarette smoke. Smoke-exposed MME
−
/
−
mice that received monthly intratracheal instillations of monocyte chemoattractant protein–1 showed accumulation of alveolar macrophages but did not develop air space enlargement. Thus, macrophage elastase is probably sufficient for the development of emphysema that results from chronic inhalation of cigarette smoke.
Nanotubule-Based Molecular-Filtration Membranes
Authors: Jirage Kshama B. , Hulteen John C. , Martin Charles R.
Published: July 2002

Polymeric membranes that contain a collection of monodisperse gold nanotubules, with inside diameters of molecular dimensions (less than 1 nanometer), were used in a simple membrane-permeation experiment to cleanly separate small molecules on the basis of molecular size. For example, when such a membrane was presented with an aqueous feed solution containing pyridine (molecular weight 79) and quinine (molecular weight 324), only the smaller pyridine molecule was transported through the nanotubules and into a receiver solution on the other side of the membrane.
Femtosecond Mid-IR Pump-Probe Spectroscopy of Liquid Water: Evidence for a Two-Component Structure
Authors: Woutersen S. , Emmerichs U. , Bakker H. J.
Published: July 2002

A femtosecond mid-infrared pump-probe study of the vibrational and orientational dynamics of the OH-stretching mode of HDO dissolved in D
2
O is presented. The orientational relaxation of the HDO molecules was observed to occur on either a very slow or a very fast time scale, with associated time constants of τ

R

= 13 picoseconds and τ

R

= 0.7 picosecond. It was observed that strongly hydrogen-bonded water molecules only relax through the slow orientational relaxation process, whereas the fast process dominates for weakly hydrogen-bonded molecules. This suggests that, with respect to orientional dynamics, two distinct molecular species exist in liquid water.
Dissociated Pattern of Activity in Visual Cortices and Their Projections During Human Rapid Eye Movement Sleep
Authors: Braun Allen R. , Balkin Thomas J. , Wesensten Nancy J. , Gwadry Fuad , Carson Richard E. , Varga Mary , Baldwin Paul , Belenky Gregory , Herscovitch Peter
Published: July 2002

Positron emission tomography was used to measure cerebral activity and to evaluate regional interrelationships within visual cortices and their projections during rapid eye movement (REM) sleep in human subjects. REM sleep was associated with selective activation of extrastriate visual cortices, particularly within the ventral processing stream, and an unexpected attenuation of activity in the primary visual cortex; increases in regional cerebral blood flow in extrastriate areas were significantly correlated with decreases in the striate cortex. Extrastriate activity was also associated with concomitant activation of limbic and paralimbic regions, but with a marked reduction of activity in frontal association areas including lateral orbital and dorsolateral prefrontal cortices. This pattern suggests a model for brain mechanisms subserving REM sleep where visual association cortices and their paralimbic projections may operate as a closed system dissociated from the regions at either end of the visual hierarchy that mediate interactions with the external world.
Chiral Spaces: Dissymmetric Capsules Through Self-Assembly
Authors: Rivera José M. , Martı́n Tomás , Rebek Julius
Published: July 2002

Molecules with self-complementary surfaces interact through weak intermolecular forces to form assemblies, and the assembled states frequently exhibit distinctive properties. Described here are systems in which symmetrical molecules assemble through hydrogen bonding to produce capsules with dissymmetric cavities. The capsules form and dissipate on a time scale that permits their direct observation by nuclear magnetic resonance measurements, and they act as hosts for smaller molecular guests. Molecular recognition of chiral guests, such as naturally occurring terpenes, determines which dissymmetric cavities are preferentially formed in the assembly process.
Biodiversity Assessment and Conservation Strategies
Authors: van Jaarsveld Albert S. , Freitag Stefanie , Chown Steven L. , Muller Caron , Koch Stephanie , Hull Heath , Bellamy Chuck , Krüger Martin , Endrödy-Younga Sebastian , Mansell Mervyn W. , Scholtz Clarke H.
Published: July 2002

The efficient representation of all species in conservation planning is problematic. Often, species distribution is assessed by dividing the land into a grid; complementary sets of grids, in which each taxon is represented at least once, are then sought. To determine if this approach provides useful surrogate information, species and higher taxon data for South African plants and animals were analyzed. Complementary species sets did not coincide and overlapped little with higher taxon sets. Survey extent and taxonomic knowledge did not affect this overlap. Thus, the assumptions of surrogacy, on which so much conservation planning is based, are not supported.
Temperature-Induced Momentum-Dependent Spectral Weight Transfer in Bi
2
Sr
2
CaCu
2
O
8+δ
Authors: Shen Z.-X. , White P. J. , Feng D. L. , Kim C. , Gu G. D. , Ikeda H. , Yoshizaki R. , Koshizuka N.
Published: July 2002

Angle-resolved photoemission data from the cuprate superconductor Bi
2
Sr
2
CaCu
2
O
8+δ
above and below the superconducting transition temperature
T
c
reveal momentum-dependent changes that extend up to an energy of about 0.3 electron volt, or 40
kT
c
(where
k
is the Boltzmann constant). The data suggest an anomalous transfer of spectral weight from one momentum to another, involving a sizable momentum transfer
Q
∼ (0.45π, 0). The observed
Q
is intriguingly near the charge-order periodicity required if fluctuating charge stripes are present.
Biodemographic Trajectories of Longevity
Authors: Vaupel James W. , Carey James R. , Christensen Kaare , Johnson Thomas E. , Yashin Anatoli I. , Holm Niels V. , Iachine Ivan A. , Kannisto Väinö , Khazaeli Aziz A. , Liedo Pablo , Longo Valter D. , Zeng Yi , Manton Kenneth G. , Curtsinger James W.
Published: July 2002

Old-age survival has increased substantially since 1950. Death rates decelerate with age for insects, worms, and yeast, as well as humans. This evidence of extended postreproductive survival is puzzling. Three biodemographic insights—concerning the correlation of death rates across age, individual differences in survival chances, and induced alterations in age patterns of fertility and mortality—offer clues and suggest research on the failure of complicated systems, on new demographic equations for evolutionary theory, and on fertility-longevity interactions. Nongenetic changes account for increases in human life-spans to date. Explication of these causes and the genetic license for extended survival, as well as discovery of genes and other survival attributes affecting longevity, will lead to even longer lives.
Visualization of the Local Insulator-Metal Transition in Pr
0.7
Ca
0.3
MnO
3
Authors: Fiebig Manfred , Miyano Kenjiro , Tomioka Yasuhide , Tokura Yoshinori
Published: July 2002

The light-induced insulator-metal transition in the “colossal magnetoresistance” compound Pr
0.7
Ca
0.3
MnO
3
is shown to generate a well-localized conducting path while the bulk of the sample remains insulating. The path can be visualized through a change of reflectivity that accompanies the phase transition. Its visibility provides a tool for gaining insight into electronic transport in materials with strong magnetic correlations. For example, a conducting path can be generated or removed at an arbitrary position just because of the presence of another path. Such manipulation may be useful in the construction of optical switches.
Neural Correlates of Perceptual Rivalry in the Human Brain
Authors: Lumer Erik D. , Friston Karl J. , Rees Geraint
Published: July 2002

When dissimilar images are presented to the two eyes, perception alternates spontaneously between each monocular view, a phenomenon called binocular rivalry. Functional brain imaging in humans was used to study the neural basis of these subjective perceptual changes. Cortical regions whose activity reflected perceptual transitions included extrastriate areas of the ventral visual pathway, and parietal and frontal regions that have been implicated in spatial attention; whereas the extrastriate areas were also engaged by nonrivalrous perceptual changes, activity in the frontoparietal cortex was specifically associated with perceptual alternation only during rivalry. These results suggest that frontoparietal areas play a central role in conscious perception, biasing the content of visual awareness toward abstract internal representations of visual scenes, rather than simply toward space.
Ultraslow Electron Spin Dynamics in GaAs Quantum Wells Probed by Optically Pumped NMR
Authors: Kuzma N. N. , Khandelwal P. , Barrett S. E. , Pfeiffer L. N. , West K. W.
Published: July 2002

Optically pumped nuclear magnetic resonance (OPNMR) measurements were performed in two different electron-doped multiple quantum well samples near the fractional quantum Hall effect ground state ν = 1/3. Below 0.5 kelvin, the spectra provide evidence that spin-reversed charged excitations of the ν = 1/3 ground state are localized over the NMR time scale of about 40 microseconds. Furthermore, by varying NMR pulse parameters, the electron spin temperature (as measured by the Knight shift) could be driven above the lattice temperature, which shows that the value of the electron spin–lattice relaxation time τ
1s
is between 100 microseconds and 500 milliseconds at ν = 1/3.
Bax and Adenine Nucleotide Translocator Cooperate in the Mitochondrial Control of Apoptosis
Authors: Marzo Isabel , Brenner Catherine , Zamzami Naoufal , Jürgensmeier Juliane M. , Susin Santos A. , Vieira Helena L. A. , Prévost Marie-Christine , Xie Zhihua , Matsuyama Shigemi , Reed John C. , Kroemer Guido
Published: July 2002

The proapoptotic Bax protein induces cell death by acting on mitochondria. Bax binds to the permeability transition pore complex (PTPC), a composite proteaceous channel that is involved in the regulation of mitochondrial membrane permeability. Immunodepletion of Bax from PTPC or purification of PTPC from Bax-deficient mice yielded a PTPC that could not permeabilize membranes in response to atractyloside, a proapoptotic ligand of the adenine nucleotide translocator (ANT). Bax and ANT coimmunoprecipitated and interacted in the yeast two-hybrid system. Ectopic expression of Bax induced cell death in wild-type but not in ANT-deficient yeast. Recombinant Bax and purified ANT, but neither of them alone, efficiently formed atractyloside-responsive channels in artificial membranes. Hence, the proapoptotic molecule Bax and the constitutive mitochondrial protein ANT cooperate within the PTPC to increase mitochondrial membrane permeability and to trigger cell death.
Synthesis of Large Arrays of Well-Aligned Carbon Nanotubes on Glass
Authors: Ren Z. F. , Huang Z. P. , Xu J. W. , Wang J. H. , Bush P. , Siegal M. P. , Provencio P. N.
Published: July 2002

Free-standing aligned carbon nanotubes have previously been grown above 700°C on mesoporous silica embedded with iron nanoparticles. Here, carbon nanotubes aligned over areas up to several square centimeters were grown on nickel-coated glass below 666°C by plasma-enhanced hot filament chemical vapor deposition. Acetylene gas was used as the carbon source and ammonia gas was used as a catalyst and dilution gas. Nanotubes with controllable diameters from 20 to 400 nanometers and lengths from 0.1 to 50 micrometers were obtained. Using this method, large panels of aligned carbon nanotubes can be made under conditions that are suitable for device fabrication.
Arctic Ozone Loss Due to Denitrification
Authors: Waibel A. E. , Peter Th. , Carslaw K. S. , Oelhaf H. , Wetzel G. , Crutzen P. J. , Pöschl U. , Tsias A. , Reimer E. , Fischer H.
Published: July 2002

Measurements from the winter of 1994–95 indicating removal of total reactive nitrogen from the Arctic stratosphere by particle sedimentation were used to constrain a microphysical model. The model suggests that denitrification is caused predominantly by nitric acid trihydrate particles in small number densities. The denitrification is shown to increase Arctic ozone loss substantially. Sensitivity studies indicate that the Arctic stratosphere is currently at a threshold of denitrification. This implies that future stratospheric cooling, induced by an increase in the anthropogenic carbon dioxide burden, is likely to enhance denitrification and to delay until late in the next century the return of Arctic stratospheric ozone to preindustrial values.
UDP-GlcNAc 2-Epimerase: A Regulator of Cell Surface Sialylation
Authors: Keppler Oliver T. , Hinderlich Stephan , Langner Josmar , Schwartz-Albiez Reinhard , Reutter Werner , Pawlita Michael
Published: July 2002

Modification of cell surface molecules with sialic acid is crucial for their function in many biological processes, including cell adhesion and signal transduction. Uridine diphosphate-
N
-acetylglucosamine 2-epimerase (UDP-GlcNAc 2-epimerase) is an enzyme that catalyzes an early, rate-limiting step in the sialic acid biosynthetic pathway. UDP-GlcNAc 2-epimerase was found to be a major determinant of cell surface sialylation in human hematopoietic cell lines and a critical regulator of the function of specific cell surface adhesion molecules.
Genetic Mechanisms of Age Regulation of Human Blood Coagulation Factor IX
Authors: Kurachi Sumiko , Deyashiki Yoshihiro , Takeshita Junko , Kurachi Kotoku
Published: July 2002

Blood coagulation capacity increases with age in healthy individuals. Through extensive longitudinal analyses of human factor IX gene expression in transgenic mice, two essential age-regulatory elements, AE5′ and AE3′, have been identified. These elements are required and together are sufficient for normal age regulation of factor IX expression. AE5′, a PEA-3 related element present in the 5′ upstream region of the gene encoding factor IX, is responsible for age-stable expression of the gene. AE3′, in the middle of the 3′ untranslated region, is responsible for age-associated elevation in messenger RNA levels. In a concerted manner, AE5′ and AE3′ recapitulate natural patterns of the advancing age–associated increase in factor IX gene expression.
Antiangiogenic Activity of the Cleaved Conformation of the Serpin Antithrombin
Authors: O'Reilly Michael S. , Pirie-Shepherd Steven , Lane William S. , Folkman Judah
Published: July 2002

Antithrombin, a member of the serpin family, functions as an inhibitor of thrombin and other enzymes. Cleavage of the carboxyl-terminal loop of antithrombin induces a conformational change in the molecule. Here it is shown that the cleaved conformation of antithrombin has potent antiangiogenic and antitumor activity in mouse models. The latent form of intact antithrombin, which is similar in conformation to the cleaved molecule, also inhibited angiogenesis and tumor growth. These data provide further evidence that the clotting and fibrinolytic pathways are directly involved in the regulation of angiogenesis.
Neuronal Activity-Dependent Cell Survival Mediated by Transcription Factor MEF2
Authors: Mao Zixu , Bonni Azad , Xia Fen , Nadal-Vicens Mireya , Greenberg Michael E.
Published: July 2002

During mammalian development, electrical activity promotes the calcium-dependent survival of neurons that have made appropriate synaptic connections. However, the mechanisms by which calcium mediates neuronal survival during development are not well characterized. A transcription-dependent mechanism was identified by which calcium influx into neurons promoted cell survival. The transcription factor MEF2 was selectively expressed in newly generated postmitotic neurons and was required for the survival of these neurons. Calcium influx into cerebellar granule neurons led to activation of p38 mitogen-activated protein kinase-dependent phosphorylation and activation of MEF2. Once activated, MEF2 regulated neuronal survival by stimulating MEF2-dependent gene transcription. These findings demonstrate that MEF2 is a calcium-regulated transcription factor and define a function for MEF2 during nervous system development that is distinct from previously well-characterized functions of MEF2 during muscle differentiation.
Identification of a Conserved Receptor-Binding Site on the Fiber Proteins of CAR-Recognizing Adenoviridae
Authors: Roelvink Peter W. , Lee Gai Mi , Einfeld David A. , Kovesdi Imre , Wickham Thomas J.
Published: July 2002

The human adenovirus serotype 5 (Ad5) is used widely for applications in human gene therapy. Cellular attachment of Ad5 is mediated by binding of the carboxyl-terminal knob of its fiber coat protein to the Coxsackie adenovirus receptor (CAR) protein. However, Ad5 binding to CAR hampers the development of adenovirus vectors capable of specifically targeting (diseased) tissues or organs. Through sequence analysis and mutagenesis, a conserved receptor-binding region was identified on the side of three divergent CAR-binding knobs. The feasibility of simultaneous CAR ablation and redirection of an adenovirus to a new receptor is demonstrated.
Dopaminergic Loss and Inclusion Body Formation in α-Synuclein Mice: Implications for Neurodegenerative Disorders
Authors: Masliah Eliezer , Rockenstein Edward , Veinbergs Isaac , Mallory Margaret , Hashimoto Makoto , Takeda Ayako , Sagara Yutaka , Sisk Abbyann , Mucke Lennart
Published: July 2002

To elucidate the role of the synaptic protein α-synuclein in neurodegenerative disorders, transgenic mice expressing wild-type human α-synuclein were generated. Neuronal expression of human α-synuclein resulted in progressive accumulation of α-synuclein—and ubiquitin-immunoreactive inclusions in neurons in the neocortex, hippocampus, and substantia nigra. Ultrastructural analysis revealed both electron-dense intranuclear deposits and cytoplasmic inclusions. These alterations were associated with loss of dopaminergic terminals in the basal ganglia and with motor impairments. These results suggest that accumulation of wild-type α-synuclein may play a causal role in Parkinson's disease and related conditions.
Motion Integration and Postdiction in Visual Awareness
Authors: Eagleman David M. , Sejnowski Terrence J.
Published: July 2002

In the flash-lag illusion, a flash and a moving object in the same location appear to be offset. A series of psychophysical experiments yields data inconsistent with two previously proposed explanations: motion extrapolation (a predictive model) and latency difference (an online model). We propose an alternative in which visual awareness is neither predictive nor online but is postdictive, so that the percept attributed to the time of the flash is a function of events that happen in the ∼80 milliseconds after the flash. The results here show how interpolation of the past is the only framework of the three models that provides a unified explanation for the flash-lag phenomenon.
Comparative Genomics of the Eukaryotes
Authors: Rubin Gerald M. , Yandell Mark D. , Wortman Jennifer R. , Gabor George L. , Miklos  , Nelson Catherine R. , Hariharan Iswar K. , Fortini Mark E. , Li Peter W. , Apweiler Rolf , Fleischmann Wolfgang , Cherry J. Michael , Henikoff Steven , Skupski Marian P. , Misra Sima , Ashburner Michael , Birney Ewan , Boguski Mark S. , Brody Thomas , Brokstein Peter , Celniker Susan E. , Chervitz Stephen A. , Coates David , Cravchik Anibal , Gabrielian Andrei , Galle Richard F. , Gelbart William M. , George Reed A. , Goldstein Lawrence S. B. , Gong Fangcheng , Guan Ping , Harris Nomi L. , Hay Bruce A. , Hoskins Roger A. , Li Jiayin , Li Zhenya , Hynes Richard O. , Jones S. J. M. , Kuehl Peter M. , Lemaitre Bruno , Littleton J. Troy , Morrison Deborah K. , Mungall Chris , O'Farrell Patrick H. , Pickeral Oxana K. , Shue Chris , Vosshall Leslie B. , Zhang Jiong , Zhao Qi , Zheng Xiangqun H. , Zhong Fei , Zhong Wenyan , Gibbs Richard , Venter J. Craig , Adams Mark D. , Lewis Suzanna
Published: July 2002

A comparative analysis of the genomes of
Drosophila melanogaster
,
Caenorhabditis elegans
, and
Saccharomyces cerevisiae
—and the proteins they are predicted to encode—was undertaken in the context of cellular, developmental, and evolutionary processes. The nonredundant protein sets of flies and worms are similar in size and are only twice that of yeast, but different gene families are expanded in each genome, and the multidomain proteins and signaling pathways of the fly and worm are far more complex than those of yeast. The fly has orthologs to 177 of the 289 human disease genes examined and provides the foundation for rapid analysis of some of the basic processes involved in human disease.
The
Drosophila
Genome Sequence: Implications for Biology and Medicine
Authors: Kornberg Thomas B. , Krasnow and Mark A.
Published: July 2002

The 120-megabase euchromatic portion of the
Drosophila melanogaster
genome has been sequenced. Because the genome is compact and many genetic tools are available, and because fly cell biology and development have much in common with mammals, this sequence may be the Rosetta stone for deciphering the human genome.