bluuebunny/crossref_metadata_2025 huggingface dataset:
Cytoskeletal Regulation by the Nedd8 Ubiquitin-Like Protein Modification Pathway
Authors: Kurz Thimo , Pintard Lionel , Willis John H. , Hamill Danielle R. , Gönczy Pierre , Peter Matthias , Bowerman Bruce
Published: July 2002

The Nedd8 ubiquitin-like protein modification pathway regulates cell-cycle progression. Our analysis of Nedd8 requirements during
Caenorhabditis elegans
embryogenesis indicates that the cytoskeleton is another target. Nedd8 conjugation negatively regulated contractility of the microfilament-rich cell cortex during pronuclear migration and again during cytokinesis. The Nedd8 pathway also was required after meiosis to negatively regulate katanin, a microtubule-severing complex, permitting the assembly of a large mitotic spindle. We propose that Nedd8-modified cullin, as part of an E3 ubiquitin ligase complex, targets katanin for degradation during the transition from meiosis to mitosis.
A Tomato Cysteine Protease Required for
Cf-2
-Dependent Disease Resistance and Suppression of Autonecrosis
Authors: Krüger Julia , Thomas Colwyn M. , Golstein Catherine , Dixon Mark S. , Smoker Matthew , Tang Saijun , Mulder Lonneke , Jones Jonathan D. G.
Published: July 2002

Little is known of how plant disease resistance (R) proteins recognize pathogens and activate plant defenses.
Rcr3
is specifically required for the function of
Cf-2
, a
Lycopersicon pimpinellifolium
gene bred into cultivated tomato (
Lycopersicon esculentum
) for resistance to
Cladosporium fulvum. Rcr3
encodes a secreted papain-like cysteine endoprotease. Genetic analysis shows
Rcr3
is allelic to the
L. pimpinellifolium Ne
gene, which suppresses the
Cf-2
–dependent autonecrosis conditioned by its
L. esculentum
allele,
ne
(
necrosis
).
Rcr3
alleles from these two species encode proteins that differ by only seven amino acids. Possible roles of Rcr3 in Cf-2–dependent defense and autonecrosis are discussed.
Observations of Comet 19P/Borrelly by the Miniature Integrated Camera and Spectrometer Aboard Deep Space 1
Authors: Soderblom L. A. , Becker T. L. , Bennett G. , Boice D. C. , Britt D. T. , Brown R. H. , Buratti B. J. , Isbell C. , Giese B. , Hare T. , Hicks M. D. , Howington-Kraus E. , Kirk R. L. , Lee M. , Nelson R. M. , Oberst J. , Owen T. C. , Rayman M. D. , Sandel B. R. , Stern S. A. , Thomas N. , Yelle R. V.
Published: July 2002

The nucleus of the Jupiter-family comet 19P/Borrelly was closely observed by the Miniature Integrated Camera and Spectrometer aboard the Deep Space 1 spacecraft on 22 September 2001. The 8-kilometer-long body is highly variegated on a scale of 200 meters, exhibiting large albedo variations (0.01 to 0.03) and complex geologic relationships. Short-wavelength infrared spectra (1.3 to 2.6 micrometers) show a slope toward the red and a hot, dry surface (≤345 kelvin, with no trace of water ice or hydrated minerals), consistent with ∼10% or less of the surface actively sublimating. Borrelly's coma exhibits two types of dust features: fans and highly collimated jets. At encounter, the near-nucleus coma was dominated by a prominent dust jet that resolved into at least three smaller jets emanating from a broad basin in the middle of the nucleus. Because the major dust jet remained fixed in orientation, it is evidently aligned near the rotation axis of the nucleus.
The Sun's Role in Climate Variations
Authors: Rind D.
Published: July 2002

Is the Sun the controller of climate changes, only the instigator of changes that are mostly forced by the system feedbacks, or simply a convenient scapegoat for climate variations lacking any other obvious cause? This question is addressed for suggested solar forcing mechanisms operating on time scales from billions of years to decades. Each mechanism fails to generate the expected climate response in important respects, although some relations are found. The magnitude of the system feedbacks or variability appears as large or larger than that of the solar forcing, making the Sun's true role ambiguous. As the Sun provides an explicit external forcing, a better understanding of its cause and effect in climate change could help us evaluate the importance of other climate forcings (such as past and future greenhouse gas changes).
Submicrometer Ferromagnetic NOT Gate and Shift Register
Authors: Allwood D. A. , Xiong Gang , Cooke M. D. , Faulkner C. C. , Atkinson D. , Vernier N. , Cowburn R. P.
Published: July 2002

An all-metallic submicrometer device is demonstrated experimentally at room temperature that performs logical NOT operations on magnetic logic signals. When this two-terminal ferromagnetic structure is incorporated into a magnetic feedback loop, the junction performs a frequency division operation on an applied oscillating magnetic field. Up to 11 of these junctions are then directly linked together to create a magnetic shift register.
Near-Infrared Spectroscopy and Spectral Mapping of Jupiter and the Galilean Satellites: Results from Galileo's Initial Orbit
Authors: Carlson R. , Smythe W. , Baines K. , Barbinis E. , Becker K. , Burns R. , Calcutt S. , Calvin W. , Clark R. , Danielson G. , Davies A. , Drossart P. , Encrenaz T. , Fanale F. , Granahan J. , Hansen G. , Herrera P. , Hibbitts C. , Hui J. , Irwin P. , Johnson T. , Kamp L. , Kieffer H. , Leader F. , Lellouch E. , Lopes-Gautier R. , Matson D. , McCord T. , Mehlman R. , Ocampo A. , Orton G. , Roos-Serote M. , Segura M. , Shirley J. , Soderblom L. , Stevenson A. , Taylor F. , Torson J. , Weir A. , Weissman P.
Published: July 2002

The Near Infrared Mapping Spectrometer performed spectral studies of Jupiter and the Galilean satellites during the June 1996 perijove pass of the Galileo spacecraft. Spectra for a 5-micrometer hot spot on Jupiter are consistent with the absence of a significant water cloud above 8 bars and with a depletion of water compared to that predicted for solar composition, corroborating results from the Galileo probe. Great Red Spot (GRS) spectral images show that parts of this feature extend upward to 240 millibars, although considerable altitude-dependent structure is found within it. A ring of dense clouds surrounds the GRS and is lower than it by 3 to 7 kilometers. Spectra of Callisto and Ganymede reveal a feature at 4.25 micrometers, attributed to the presence of hydrated minerals or possibly carbon dioxide on their surfaces. Spectra of Europa's high latitudes imply that fine-grained water frost overlies larger grains. Several active volcanic regions were found on Io, with temperatures of 420 to 620 kelvin and projected areas of 5 to 70 square kilometers.
Epitaxial YBa
2
Cu
3
O
7
on Biaxially Textured Nickel (001): An Approach to Superconducting Tapes with High Critical Current Density
Authors: Norton David P. , Goyal Amit , Budai John D. , Christen David K. , Kroeger Donald M. , Specht Eliot D. , He Qing , Saffian Bernd , Paranthaman M. , Klabunde Charles E. , Lee Dominic F. , Sales Brian C. , List Fred A.
Published: July 2002

In-plane-aligned,
c
axis-oriented YBa
2
Cu
3
O
7
(YBCO) films with superconducting critical current densities
J
c
as high as 700,000 amperes per square centimeter at 77 kelvin have been grown on thermomechanically rolled-textured nickel (001) tapes by pulsed-laser deposition. Epitaxial growth of oxide buffer layers directly on biaxially textured nickel, formed by recrystallization of cold-rolled pure nickel, made possible the growth of YBCO films 1.5 micrometers thick with superconducting properties that are comparable to those observed for epitaxial films on single-crystal oxide substrates. This result represents a viable approach for the production of long superconducting tapes for high-current, high-field applications at 77 kelvin.
Behind the Official Optimism, Flawed Projections
Authors: Glanz James
Published: July 2002

Confidence in plans for the huge fusion-energy test-bed called ITER are being shaken not just by a new theory of plasma turbulence (see accompanying
story
) but also by an analysis of the ITER project's own optimistic projections of the machine's performance. Those projections are based on extrapolations from the performance of existing tokamaks, but now it seems that the extrapolations may have serious mathematical flaws.
The Metal-Insulator Transition in Correlated Disordered Systems
Authors: Abrahams Elihu , Kotliar Gabriel
Published: July 2002

Some materials are metals and conduct electricity well; others are insulators and do not. In some cases, metals can be converted to insulators and vice versa by changing some fundamental parameter, such as pressure. In their Perspective, Abrahams and Kotliar discuss results reported in the same issue by Husmann
et al
. (
p. 1874
) in which a continuous metal-insulator transition has been observed in a nickel selenide-sulfide compound. Understanding such transitions, which have posed puzzles for years, may help unravel the physics of highly correlated electrons, as well as lead to new materials.
Double Helix Does Chemistry at a Distance—But How?
Authors: Taubes Gary
Published: July 2002

Add yet another startling ability to the DNA résumé. A Report in this issue (
p. 1465
) presents evidence that the DNA double helix can perform chemistry at a distance. When light strikes a metal complex tethered to one end of a DNA molecule, a chemical change takes place far down the helix, causing a patch of damaged DNA to be mended. The feat supports the controversial possibility that DNA's unique structure allows it to behave like a conductive wire, which would be an even more impressive attribute.
A Membrane Network for Nutrient Import in Red Cells Infected with the Malaria Parasite
Authors: Lauer Sabine A. , Rathod Pradipsinh K. , Ghori Nafisa , Haldar Kasturi
Published: July 2002

The human malaria parasite
Plasmodium falciparum
exports an interconnected network of tubovesicular membranes (the TVM) that extends from the parasite’s vacuolar membrane to the periphery of the red cell. Here it is shown that extracellular solutes such as Lucifer yellow enter the TVM and are delivered to the parasite. Blocking the assembly of the network blocked the delivery of exogenous Lucifer yellow, nucleosides, and amino acids to the parasite without inhibiting secretion of plasmodial proteins. These data suggest that the TVM is a transport network that allows nutrients efficient access to the parasite and could be used to deliver antimalarial drugs directly into the parasite.
Regulation of Mitochondrial Iron Accumulation by Yfh1p, a Putative Homolog of Frataxin
Authors: Babcock Michael , de Silva Deepika , Oaks Robert , Davis-Kaplan Sandra , Jiralerspong Sarn , Montermini Laura , Pandolfo Massimo , Kaplan Jerry
Published: July 2002

The gene responsible for Friedreich's ataxia, a disease characterized by neurodegeneration and cardiomyopathy, has recently been cloned and its product designated frataxin. A gene in
Saccharomyces cerevisiae
was characterized whose predicted protein product has high sequence similarity to the human frataxin protein. The yeast gene (yeast frataxin homolog,
YFH1
) encodes a mitochondrial protein involved in iron homeostasis and respiratory function. Human frataxin also was shown to be a mitochondrial protein. Characterizing the mechanism by which
YFH1
regulates iron homeostasis in yeast may help to define the pathologic process leading to cell damage in Friedreich's ataxia.
Natural (Mg,Fe)SiO
3
-Ilmenite and -Perovskite in the Tenham Meteorite
Authors: Tomioka Naotaka , Fujino Kiyoshi
Published: July 2002

The minerals (Mg,Fe)SiO
3
-ilmenite and -perovskite were identified in the shock-induced veins in the Tenham chondritic meteorite. Both phases are inferred to have transformed from pyroxene at high pressures and temperatures by shock metamorphism. Columnar-shaped ilmenite grains, one of two types of morphologies, have a topotaxial relationship with neighboring pyroxene grains, indicating shear transformation. Granular-shaped perovskite grains showed a diffraction pattern consistent with orthorhombic perovskite, but these grains were not stable under the electron beam irradiation and became amorphous. The higher iron concentration in both phases compared with those experimentally reported may suggest their metastable transition from enstatite because of shock compression.
X-rays and Fluctuating X-Winds from Protostars
Authors: Shu Frank H. , Shang Hsien , Glassgold Alfred E. , Lee Typhoon
Published: July 2002

Protostars emit more x-rays, hard and soft, than young sunlike stars in more advanced stages of formation. The x-ray emission becomes harder and stronger during flares. The excess x-rays may arise as a result of the time-dependent interaction of an accretion disk with the magnetosphere of the central star. Flares produced by such fluctuations have important implications for the x-wind model of protostellar jets, for the flash-heating of the chondrules found in chondritic meteorites, and for the production of short-lived radioactivities through the bombardment of primitive rocks by solar cosmic rays.
Counteraction by MutT Protein of Transcriptional Errors Caused by Oxidative Damage
Authors: Taddei F. , Hayakawa H. , Bouton M.-F. , Cirinesi A.-M. , Matic I. , Sekiguchi M. , Radman M.
Published: July 2002

Oxidized guanine (8-oxo-7,8-dihydroguanine; 8-oxo-G) is a potent mutagen because of its ambiguous pairing with cytosine and adenine. The
Escherichia coli
MutT protein specifically hydrolyzes both 8-oxo-deoxyguanosine triphosphate (8-oxo-dGTP) and 8-oxo-guanosine triphosphate (8-oxo-rGTP), which are otherwise incorporated in DNA and RNA opposite template A. In vivo, this cleaning of the nucleotide pools decreases both DNA replication and transcription errors. The effect of
mutT
mutation on transcription fidelity was shown to depend on oxidative metabolism. Such control of transcriptional fidelity by the ubiquitous MutT function has implications for evolution of RNA-based life, phenotypic expression, adaptive mutagenesis, and functional maintenance of nondividing cells.
Probing Single Secretory Vesicles with Capillary Electrophoresis
Authors: Chiu Daniel T. , Lillard Sheri J. , Scheller Richard H. , Zare Richard N. , Rodriguez-Cruz Sandra E. , Williams Evan R. , Orwar Owe , Sandberg Mats , Lundqvist J. Anders
Published: July 2002

Secretory vesicles obtained from the atrial gland of the gastropod mollusk
Aplysia californica
were chemically analyzed individually with a combination of optical trapping, capillary electrophoresis separation, and a laser-induced fluorescence detection. With the use of optical trapping, a single vesicle that had attoliters (10
−18
liters) of volume was introduced into the tapered inlet of a separation capillary. Once the vesicle was injected, it was lysed, and its components were fluorescently labeled with naphthalene-2,3-dicarboxaldehyde before separation. The resultant electropherograms indicated distinct variations in the contents of single vesicles.
Hyperinnervation of Neuromuscular Junctions Caused by GDNF Overexpression in Muscle
Authors: Nguyen Quyen T. , Parsadanian Alexander Sh. , Snider William D. , Lichtman Jeff W.
Published: July 2002

Overexpression of glial cell line–derived neurotrophic factor (GDNF) by muscle greatly increased the number of motor axons innervating neuromuscular junctions in neonatal mice. The extent of hyperinnervation correlated with the amount of GDNF expressed in four transgenic lines. Overexpression of GDNF by glia and overexpression of neurotrophin-3 and neurotrophin-4 in muscle did not cause hyperinnervation. Thus, increased amounts of GDNF in postsynaptic target cells can regulate the number of innervating axons.
Detection of H
3
+
in the Diffuse Interstellar Medium Toward Cygnus OB2 No. 12
Authors: McCall B. J. , Geballe T. R. , Hinkle K. H. , Oka T.
Published: July 2002

The molecular ion H
3
+
is considered the cornerstone of interstellar chemistry because it initiates the reactions responsible for the production of many larger molecules. Recently discovered in dense molecular clouds, H
3
+
has now been observed in the diffuse interstellar medium toward Cygnus OB2 No. 12. Analysis of H
3
+
chemistry suggests that the high H
3
+
column density (3.8 × 10
14
per square centimeter) is due not to a high H
3
+
concentration but to a long absorption path. This and other work demonstrate the ubiquity of H
3
+
and its potential as a probe of the physical and chemical conditions in the interstellar medium.
Intense Sub-Kilometer-Scale Boundary Layer Rolls Observed in Hurricane Fran
Authors: Wurman Joshua , Winslow Jennifer
Published: July 2002

High-resolution observations obtained with the Doppler On Wheels (DOW) mobile weather radar near the point of landfall of hurricane Fran (1996) revealed the existence of intense, sub-kilometer-scale, boundary layer rolls that strongly modulated the near-surface wind speed. It is proposed that these structures are one cause of geographically varying surface damage patterns that have been observed after some landfalling hurricanes and that they cause much of the observed gustiness, bringing high-velocity air from aloft to the lowest observable levels. High-resolution DOW radar observations are contrasted with lower-resolution observations obtained with an operational weather radar, which underestimated peak low-level wind speeds.
Nucleation of COPII Vesicular Coat Complex by Endoplasmic Reticulum to Golgi Vesicle SNAREs
Authors: Springer Sebastian , Schekman Randy
Published: July 2002

Protein trafficking from the endoplasmic reticulum (ER) to the Golgi apparatus involves specific uptake into coat protein complex II (COPII)–coated vesicles of secretory and of vesicle targeting (v-SNARE) proteins. Here, two ER to Golgi v-SNAREs, Bet1p and Bos1p, were shown to interact specifically with Sar1p, Sec23p, and Sec24p, components of the COPII coat, in a guanine nucleotide–dependent fashion. Other v-SNAREs, Sec22p and Ykt6p, might interact more weakly with the COPII coat or interact indirectly by binding to Bet1p or Bos1p. The data suggest that transmembrane proteins can be taken up into COPII vesicles by direct interactions with the coat proteins and may play a structural role in the assembly of the COPII coat complex.
Positive Selection Through a Motif in the αβ T Cell Receptor
Authors: Bäckström B. Thomas , Müller Urs , Hausmann Barbara , Palmer Ed
Published: July 2002

The two lineages of T cells, αβ and γδ, differ in their developmental requirements: only αβ T cells require major histocompatibility complex recognition, a process known as positive selection. The αβ T cell receptor (TCR), but not its γδ counterpart, contains a motif within the α-chain connecting peptide domain (α-CPM) that has been conserved over the last 500 million years. In transgenic mice expressing an αβ TCR lacking the α-CPM, thymocytes were blocked in positive selection but could undergo negative selection. Thus, the α-CPM seems to participate in the generation of signals required for positive selection.
Sex and Conflict
Authors: Partridge Linda , Hurst Laurence D.
Published: July 2002

REVIEW

Evolutionary conflict occurs when the deterministic spread of an allele lowers the fitness either of its bearer or of other individuals in the population, leading to selection for suppressors. Sex promotes conflict because associations between alleles are temporary. Differing selection on males and females, sexual selection, and differences in transmission patterns between classes of nuclear and cytoplasmic genes can all give rise to conflict. Inert Y chromosomes, uniparental inheritance of cytoplasmic genes, mating strains and sexes, and many features of sexual behavior may have evolved in part as a result of evolutionary conflict. Estimates of its quantitative importance, however, are still needed.
Climate Change Record in Subsurface Temperatures: A Global Perspective
Authors: Pollack Henry N. , Huang Shaopeng , Shen Po-Yu
Published: July 2002

Analyses of underground temperature measurements from 358 boreholes in eastern North America, central Europe, southern Africa, and Australia indicate that, in the 20th century, the average surface temperature of Earth has increased by about 0.5°C and that the 20th century has been the warmest of the past five centuries. The subsurface temperatures also indicate that Earth's mean surface temperature has increased by about 1.0°C over the past five centuries. The geothermal data offer an independent confirmation of the unusual character of 20th-century climate that has emerged from recent multiproxy studies.
A Long-Snouted Predatory Dinosaur from Africa and the Evolution of Spinosaurids
Authors: Sereno Paul C. , Beck Allison L. , Dutheil Didier B. , Gado Boubacar , Larsson Hans C. E. , Lyon Gabrielle H. , Marcot Jonathan D. , Rauhut Oliver W. M. , Sadleir Rudyard W. , Sidor Christian A. , Varricchio David D. , Wilson Gregory P. , Wilson Jeffrey A.
Published: July 2002

Fossils discovered in Lower Cretaceous (Aptian) rocks in the Ténéré Desert of central Niger provide new information about spinosaurids, a peculiar group of piscivorous theropod dinosaurs. The remains, which represent a new genus and species, reveal the extreme elongation and transverse compression of the spinosaurid snout. The postcranial bones include blade-shaped vertebral spines that form a low sail over the hips. Phylogenetic analysis suggests that the enlarged thumb claw and robust forelimb evolved during the Jurassic, before the elongated snout and other fish-eating adaptations in the skull. The close phylogenetic relationship between the new African spinosaurid and
Baryonyx
from Europe provides evidence of dispersal across the Tethys seaway during the Early Cretaceous.
Atomic Contributions to the Optical Rotation Angle as a Quantitative Probe of Molecular Chirality
Authors: Kondru Rama K. , Wipf Peter , Beratan David N.
Published: July 2002

Chiral molecules are characterized by a specific rotation angle, the angle through which plane-polarized light is rotated on passing through an enantiomerically enriched solution. Recent developments in methodology allow computation of both the sign and the magnitude of these rotation angles. However, a general strategy for assigning the individual contributions that atoms and functional groups make to the optical rotation angle and, more generally, to the molecular chirality has remained elusive. Here, a method to determine the atomic contributions to the optical rotation angle is reported. This approach links chemical structure with optical rotation angle and provides a quantitative measure of molecular asymmetry propagation from a center, axis, or plane of chirality.
Efficient Bypass of a Thymine-Thymine Dimer by Yeast DNA Polymerase, Polη
Authors: Johnson Robert E. , Prakash Satya , Prakash Louise
Published: July 2002

The
RAD30
gene of the yeast
Saccharomyces cerevisiae
is required for the error-free postreplicational repair of DNA that has been damaged by ultraviolet irradiation. Here,
RAD30
is shown to encode a DNA polymerase that can replicate efficiently past a thymine-thymine
cis-syn
cyclobutane dimer, a lesion that normally blocks DNA polymerases. When incubated in vitro with all four nucleotides, Rad30 incorporates two adenines opposite the thymine-thymine dimer. Rad30 is the seventh eukaryotic DNA polymerase to be described and hence is named DNA polymerase η.
Requirement for Croquemort in Phagocytosis of Apoptotic Cells in
Drosophila
Authors: Franc Nathalie C. , Heitzler Pascal , Alan B. R. , Ezekowitz  , White Kristin
Published: July 2002

Macrophages in the
Drosophila
embryo are responsible for the phagocytosis of apoptotic cells and are competent to engulf bacteria. Croquemort (CRQ) is a CD36-related receptor expressed exclusively on these macrophages. Genetic evidence showed that
crq
was essential for efficient phagocytosis of apoptotic corpses but was not required for the engulfment of bacteria. The expression of CRQ was regulated by the amount of apoptosis. These data define distinct pathways for the phagocytosis of corpses and bacteria in
Drosophila
.
The Role of Sub-Milankovitch Climatic Forcing in the Initiation of the Northern Hemisphere Glaciation
Authors: Willis K. J. , Kleczkowski A. , Briggs K. M. , Gilligan C. A.
Published: July 2002

Mechanisms responsible for the initiation of major glaciation in the Northern Hemisphere at about 2.75 million years ago are poorly understood. A laminated terrestrial sequence from Pula maar, Hungary, containing about 320,000 years in annual layers between 3.05 and 2.60 million years ago, provides a detailed record of rates of climatic change across this dramatic transition. An analysis of the record implies that climatic variations at sub-Milankovitch frequencies (less than or equal to 15,000 years) were an important driving force during this transitional interval and that, as the threshold was approached, these increased in frequency and amplitude, possibly providing the final trigger for the amplification of Northern Hemisphere ice sheets.
The U.S. Carbon Budget: Contributions from Land-Use Change
Authors: Houghton R. A. , Hackler J. L. , Lawrence K. T.
Published: July 2002

The rates at which lands in the United States were cleared for agriculture, abandoned, harvested for wood, and burned were reconstructed from historical data for the period 1700–1990 and used in a terrestrial carbon model to calculate annual changes in the amount of carbon stored in terrestrial ecosystems, including wood products. Changes in land use released 27 ± 6 petagrams of carbon to the atmosphere before 1945 and accumulated 2 ± 2 petagrams of carbon after 1945, largely as a result of fire suppression and forest growth on abandoned farmlands. During the 1980s, the net flux of carbon attributable to land management offset 10 to 30 percent of U.S. fossil fuel emissions.
Current-Induced Switching of Domains in Magnetic Multilayer Devices
Authors: Myers E. B. , Ralph D. C. , Katine J. A. , Louie R. N. , Buhrman R. A.
Published: July 2002

Current-induced switching in the orientation of magnetic moments is observed in cobalt/copper/cobalt sandwich structures, for currents flowing perpendicularly through the layers. Magnetic domains in adjacent cobalt layers can be manipulated controllably between stable parallel and antiparallel configurations by applying current pulses of the appropriate sign. The observations are in accord with predictions that a spin-polarized current exerts a torque at the interface between a magnetic and nonmagnetic metal, due to local exchange interactions between conduction electrons and the magnetic moments.
Fungal Endophyte Symbiosis and Plant Diversity in Successional Fields
Authors: Clay Keith , Holah Jenny
Published: July 2002

Increasing evidence suggests that microbial interactions are important determinants of plant biodiversity. The hypothesis that fungal endophyte symbiosis reduces diversity in successional fields was tested by manipulating infection of tall fescue, the most abundant perennial grass in the eastern United States. Over a 4-year period, species richness declined and tall fescue dominance increased in infected plots relative to uninfected plots without differences in total productivity. A host-specific endophyte, with negligible biomass, altered plant community structure in this long-term field experiment and may be reducing plant diversity throughout its expanding range.
Neanderthal Cannibalism at Moula-Guercy, Ardèche, France
Authors: Defleur Alban , White Tim , Valensi Patricia , Slimak Ludovic , Crégut-Bonnoure Évelyne
Published: July 2002

The cave site of Moula-Guercy, 80 meters above the modern Rhone River, was occupied by Neanderthals approximately 100,000 years ago. Excavations since 1991 have yielded rich paleontological, paleobotanical, and archaeological assemblages, including parts of six Neanderthals. The Neanderthals are contemporary with stone tools and faunal remains in the same tightly controlled stratigraphic and spatial contexts. The inference of Neanderthal cannibalism at Moula-Guercy is based on comparative analysis of hominid and ungulate bone spatial distributions, modifications by stone tools, and skeletal part representations.
Bidirectional Semiconductor Laser
Authors: Gmachl Claire , Tredicucci Alessandro , Sivco Deborah L. , Hutchinson Albert L. , Capasso Federico , Cho Alfred Y.
Published: July 2002

A semiconductor laser capable of operating under both positive and negative bias voltage is reported. Its active region behaves functionally as two different laser materials, emitting different wavelengths, depending on the design, when biased with opposite polarities. This concept was used for the generation of two wavelengths (6.3 and 6.5 micrometers) in the midinfrared region of the spectrum from a single quantum cascade laser structure. The two wavelengths are excited independently of each other and separated in time. This may have considerable impact on various semiconductor laser applications including trace gas analysis in remote sensing applications with differential absorption spectroscopy.
A Possible 20th-Century Slowdown of Southern Ocean Deep Water Formation
Authors: Broecker Wallace S. , Sutherland Stewart , Peng Tsung-Hung
Published: July 2002

Chlorofluorocarbon-11 inventories for the deep Southern Ocean appear to confirm physical oceanographic and geochemical studies in the Southern Ocean, which suggest that no more than 5 × 10
6
cubic meters per second of ventilated deep water is currently being produced. This result conflicts with conclusions based on the distributions of the carbon-14/carbon ratio and a quasi-conservative property, PO
4
*
, in the deep sea, which seem to require an average of about 15 × 10
6
cubic meters per second of Southern Ocean deep ventilation over about the past 800 years. A major reduction in Southern Ocean deep water production during the 20th century (from high rates during the Little Ice Age) may explain this apparent discordance. If this is true, a seesawing of deep water production between the northern Atlantic and Southern oceans may lie at the heart of the 1500-year ice-rafting cycle.
Cretaceous Sauropods from the Sahara and the Uneven Rate of Skeletal Evolution Among Dinosaurs
Authors: Sereno Paul C. , Beck Allison L. , Dutheil Didier B. , Larsson Hans C. E. , Lyon Gabrielle H. , Moussa Bourahima , Sadleir Rudyard W. , Sidor Christian A. , Varricchio David J. , Wilson Gregory P. , Wilson Jeffrey A.
Published: July 2002

Lower Cretaceous fossils from central Niger document the succession of sauropod dinosaurs on Africa as it drifted into geographic isolation. A new broad-toothed genus of Neocomian age (∼135 million years ago) shows few of the specializations of other Cretaceous sauropods. A new small-bodied sauropod of Aptian-Albian age (∼110 million years ago), in contrast, reveals the highly modified cranial form of rebbachisaurid diplodocoids. Rates of skeletal change in sauropods and other major groups of dinosaurs are estimated quantitatively and shown to be highly variable.
Evidence for DNA Loss as a Determinant of Genome Size
Authors: Petrov Dmitri A. , Sangster Todd A. , Johnston J. Spencer , Hartl Daniel L. , Shaw Kerry L.
Published: July 2002

Eukaryotic genome sizes range over five orders of magnitude. This variation cannot be explained by differences in organismic complexity (the
C
value paradox). To test the hypothesis that some variation in genome size can be attributed to differences in the patterns of insertion and deletion (indel) mutations among organisms, this study examines the indel spectrum in
Laupala
crickets, which have a genome size 11 times larger than that of
Drosophila
. Consistent with the hypothesis, DNA loss is more than 40 times slower in
Laupala
than in
Drosophila
.
Rippling Instability of a Collapsing Bubble
Authors: Silveira Rava da , Chaı̈eb Sahraoui , Mahadevan L.
Published: July 2002

When a bubble of air rises to the top of a highly viscous liquid, it forms a dome-shaped protuberance on the free surface. Unlike a soap bubble, it bursts so slowly as to collapse under its own weight simultaneously, and folds into a wavy structure. This rippling effect occurs for both elastic and viscous sheets, and a theory for its onset is formulated. The growth of the corrugation is governed by the competition between gravitational and bending (shearing) forces and is exhibited for a range of densities, stiffnesses (viscosities), and sizes—a result that arises less from dynamics than from geometry, suggesting a wide validity. A quantitative expression for the number of ripples is presented, together with experimental results that support the theoretical predictions.
General Acid-Base Catalysis in the Mechanism of a Hepatitis Delta Virus Ribozyme
Authors: Nakano Shu-ichi , Chadalavada Durga M. , Bevilacqua Philip C.
Published: July 2002

Many protein enzymes use general acid-base catalysis as a way to increase reaction rates. The amino acid histidine is optimized for this function because it has a p
K
a
(where
K
a
is the acid dissociation constant) near physiological pH. The RNA enzyme (ribozyme) from hepatitis delta virus catalyzes self-cleavage of a phosphodiester bond. Reactivity-pH profiles in monovalent or divalent cations, as well as distance to the leaving-group oxygen, implicate cytosine 75 (C75) of the ribozyme as the general acid and ribozyme-bound hydrated metal hydroxide as the general base in the self-cleavage reaction. Moreover, C75 has a p
K
a
perturbed to neutrality, making it “histidine-like.” Anticooperative interaction is observed between protonated C75 and a metal ion, which serves to modulate the p
K
a
of C75. General acid-base catalysis expands the catalytic repertoire of RNA and may provide improved rate acceleration.
Isotope Fractionation and Atmospheric Oxygen: Implications for Phanerozoic O
2
Evolution
Authors: Berner R. A. , Petsch S. T. , Lake J. A. , Beerling D. J. , Popp B. N. , Lane R. S. , Laws E. A. , Westley M. B. , Cassar N. , Woodward F. I. , Quick W. P.
Published: July 2002

Models describing the evolution of the partial pressure of atmospheric oxygen over Phanerozoic time are constrained by the mass balances required between the inputs and outputs of carbon and sulfur to the oceans. This constraint has limited the applicability of proposed negative feedback mechanisms for maintaining levels of atmospheric O
2
at biologically permissable levels. Here we describe a modeling approach that incorporates O
2
-dependent carbon and sulfur isotope fractionation using data obtained from laboratory experiments on carbon-13 discrimination by vascular land plants and marine plankton. The model allows us to calculate a Phanerozoic O
2
history that agrees with independent models and with biological and physical constraints and supports the hypothesis of a high atmospheric O
2
content during the Carboniferous (300 million years ago), a time when insect gigantism was widespread.
Stable Versions of Transient Push-Pull Carbenes: Extending Lifetimes from Nanoseconds to Weeks
Authors: Buron Christophe , Gornitzka Heinz , Romanenko Vadim , Bertrand Guy
Published: July 2002

A (phosphanyl)(trifluoromethyl)carbene is shown to be stable for weeks in solution at temperatures up to −30°C. Its chemical behavior exactly matches that of its transient congeners, even to the extent that subtle effects, such as the recently discovered weak π interaction with aromatics, are observed. The influence of substituents on the structure of push-pull carbenes is demonstrated by a single-crystal x-ray diffraction study of a (phosphanyl)[2,6-bis(trifluoromethyl)phenyl]carbene. The lifetime of these molecules makes them accessible to a wider range of standard techniques, allowing their chemical and physical behaviors to be studied in more detail than was previously possible.
Distinct Classes of Yeast Promoters Revealed by Differential TAF Recruitment
Authors: Li Xiao-Yong , Bhaumik Sukesh R. , Green Michael R.
Published: July 2002

The transcription factor TFIID contains the TATA box binding protein (TBP) and multiple TBP-associated factors (TAFs). Here, the association of TFIID components with promoters that either are dependent on multiple TAFs (TAF
dep
) or have no apparent TAF requirement (TAF
ind
) is analyzed in yeast. At TAF
dep
promoters, TAFs are present at levels comparable to that of TBP, whereas at TAF
ind
promoters, TAFs are present at levels that approximate background. After inactivation of several general transcription factors, including TBP, TAFs are still recruited by activators to TAF
dep
promoters. The results reveal two classes of promoters: at TAF
ind
promoters, TBP is recruited in the apparent absence of TAFs, whereas at TAF
dep
promoters, TAFs are co-recruited with TBP in a manner consistent with direct activator-TAF interactions.
Gatekeepers of the Nucleus
Authors: Wente Susan R.
Published: July 2002

Nuclear pore complexes (NPCs) form the site for entry and exit from the nucleus. A convergence of studies have defined the physical framework for the nuclear transport mechanism. This includes definition of the soluble transport machinery required for protein and RNA movement, x-ray structure analysis of transport factors, definitive compositional analysis of yeast NPCs, and documentation of the relative steady state arrangement of NPC components within the portal. With this information, researchers are now in the exciting position to examine the dynamic interplay between shuttling transport factors and the static pore complex.
Global AIDS Epidemic: Time to Turn the Tide
Authors: Piot Peter
Published: July 2002

HIV/AIDS is catastrophic both from a public health perspective and in terms of its impact on economic and social stability in many of the most severely affected nations, including virtually all of southern Africa. A public health response alone is insufficient to address this devastating epidemic. Political leadership at the highest levels is needed to mobilize a multisectoral response to the impact of HIV/AIDS on educational systems, industry, agriculture, the military, and other sectors. With a few notable exceptions, political response was slow to mobilize in the early years of the epidemic, but response has dramatically improved in the past 18 months. The Joint United Nations Programme on HIV/AIDS (UNAIDS) is involved in ongoing efforts to encourage political leaders to make a multisectoral response to the epidemic a major focus of their national plans.
Induction of Mating in
Candida albicans
by Construction of
MTL
a and
MTL
α Strains
Authors: Magee B. B. , Magee P. T.
Published: July 2002

Although the diploid fungus
Candida albicans
, a human pathogen, has been thought to have no sexual cycle, it normally possesses mating-type–like orthologs (
MTL
) of both of the
Saccharomyces cerevisiae
mating-type genes (
MAT
)
a
and α. When strains containing only
MTL
a
or
MTL
α were constructed by the loss of one homolog of chromosome 5, the site of the
MTL
loci,
MTL
a
and
MTL
α strains mated, but like mating types did not. Evidence for mating included formation of stable prototrophs from strains with complementing auxotrophic markers; these contained both
MTL
alleles and molecular markers from both parents and were tetraploid in DNA content and mononucleate.
Evidence for the Prion Hypothesis: Induction of the Yeast [

PSI
+

] Factor by in Vitro- Converted Sup35 Protein
Authors: Sparrer Helmut E. , Santoso Alex , Szoka Francis C. , Weissman Jonathan S.
Published: July 2002

Starting with purified, bacterially produced protein, we have created a [

PSI
+

]-inducing agent based on an altered (prion) conformation of the yeast Sup35 protein. After converting Sup35p to its prion conformation in vitro, we introduced it into the cytoplasm of living yeast using a liposome transformation protocol. Introduction of substoichiometric quantities of converted Sup35p greatly increased the rate of appearance of the well-characterized epigenetic factor [

PSI
+

], which results from self-propagating aggregates of cellular Sup35p. Thus, as predicted by the prion hypothesis, proteins can act as infectious agents by causing self-propagating conformational changes.
CikA, a Bacteriophytochrome That Resets the Cyanobacterial Circadian Clock
Authors: Schmitz Oliver , Katayama Mitsunori , Williams Stanly B. , Kondo Takao , Golden Susan S.
Published: July 2002

The circadian oscillator of the cyanobacterium
Synechococcus elongatus
, like those in eukaryotes, is entrained by environmental cues. Inactivation of the gene
cikA
(circadian input kinase) shortens the circadian period of gene expression rhythms in
S
.
elongatus
by approximately 2 hours, changes the phasing of a subset of rhythms, and nearly abolishes resetting of phase by a pulse of darkness. The CikA protein sequence reveals that it is a divergent bacteriophytochrome with characteristic histidine protein kinase motifs and a cryptic response regulator motif. CikA is likely a key component of a pathway that provides environmental input to the circadian oscillator in
S
.
elongatus
.
Pol κ: A DNA Polymerase Required for Sister Chromatid Cohesion
Authors: Wang Zhenghe , Castaño Irene B. , De Las Peñas Alejandro , Adams Carrie , Christman Michael F.
Published: July 2002

Establishment of cohesion between sister chromatids is coupled to replication fork passage through an unknown mechanism. Here we report that
TRF4
, an evolutionarily conserved gene necessary for chromosome segregation, encodes a DNA polymerase with β-polymerase–like properties. A double mutant in the redundant homologs,
TRF4
and
TRF5
, is unable to complete S phase, whereas a
trf4
single mutant completes a presumably defective S phase that results in a failure of cohesion between the replicated sister chromatids. This suggests that
TRF
s are a key link in the coordination between DNA replication and sister chromatid cohesion. Trf4 and Trf5 represent the fourth class of essential nuclear DNA polymerases (designated DNA polymerase kappa) in
Saccharomyces cerevisiae
and probably in all eukaryotes.
Climate Impact of Late Quaternary Equatorial Pacific Sea Surface Temperature Variations
Authors: Lea David W. , Pak Dorothy K. , Spero Howard J.
Published: July 2002

Magnesium/calcium data from planktonic foraminifera in equatorial Pacific sediment cores demonstrate that tropical Pacific sea surface temperatures (SSTs) were 2.8° ± 0.7°C colder than the present at the last glacial maximum. Glacial-interglacial temperature differences as great as 5°C are observed over the last 450 thousand years. Changes in SST coincide with changes in Antarctic air temperature and precede changes in continental ice volume by about 3 thousand years, suggesting that tropical cooling played a major role in driving ice-age climate. Comparison of SST estimates from eastern and western sites indicates that the equatorial Pacific zonal SST gradient was similar or somewhat larger during glacial episodes. Extraction of a salinity proxy from the magnesium/calcium and oxygen isotope data indicates that transport of water vapor into the western Pacific was enhanced during glacial episodes.
Increase of Maximum Life-Span in Sweden, 1861-1999
Authors: Wilmoth J. R. , Deegan L. J. , Lundström H. , Horiuchi S.
Published: July 2002

A fundamental question in aging research is whether humans and other species possess an immutable life-span limit. We examined the maximum age at death in Sweden, which rose from about 101 years during the 1860s to about 108 years during the 1990s. The pace of increase was 0.44 years per decade before 1969 but accelerated to 1.11 years per decade after that date. More than 70 percent of the rise in the maximum age at death from 1861 to 1999 is attributable to reductions in death rates above age 70. The rest are due to increased numbers of survivors to old age (both larger birth cohorts and increased survivorship from infancy to age 70). The more rapid rise in the maximum age since 1969 is due to the faster pace of old-age mortality decline during recent decades.
Signal-Processing Machines at the Postsynaptic Density
Authors: Kennedy Mary B.
Published: July 2002

Dendrites of individual neurons in the vertebrate central nervous system are contacted by thousands of synaptic terminals relaying information about the environment. The postsynaptic membrane at each synaptic terminal is the first place where information is processed as it converges on the dendrite. At the postsynaptic membrane of excitatory synapses, neurotransmitter receptors are attached to large protein “signaling machines” that delicately regulate the strength of synaptic transmission. These machines are visible in the electron microscope and are called the postsynaptic density. By changing synaptic strength in response to neural activity, the postsynaptic density contributes to information processing and the formation of memories.
Survival for Immunity: The Price of Immune System Activation for Bumblebee Workers
Authors: Moret Yannick , Schmid-Hempel Paul
Published: July 2002

Parasites do not always harm their hosts because the immune system keeps an infection at bay. Ironically, the cost of using immune defenses could itself reduce host fitness. This indirect cost of parasitism is often not visible because of compensatory resource intake. Here, workers of the bumblebee,
Bombus terrestris
, were challenged with lipopolysaccharides and micro–latex beads to induce their immune system under starvation (i.e., not allowing compensatory intake). Compared with controls, survival of induced workers was significantly reduced (by 50 to 70%).
Tunable Resistance of a Carbon Nanotube-Graphite Interface
Authors: Paulson S. , Helser A. , Nardelli M. Buongiorno , Taylor R. M. , Falvo M. , Superfine R. , Washburn S.
Published: July 2002

The transfer of electrons from one material to another is usually described in terms of energy conservation, with no attention being paid to momentum conservation. Here we present results on the junction resistance between a carbon nanotube and a graphite substrate and show that details of momentum conservation also can change the contact resistance. By changing the angular alignment of the atomic lattices, we found that contact resistance varied by more than an order of magnitude in a controlled and reproducible fashion, indicating that momentum conservation, in addition to energy conservation, can dictate the junction resistance in graphene systems such as carbon nanotube junctions and devices.
Modern Human Ancestry at the Peripheries: A Test of the Replacement Theory
Authors: Wolpoff Milford H. , Hawks John , Frayer David W. , Hunley Keith
Published: July 2002

The replacement theory of modern human origins stipulates that populations outside of Africa were replaced by a new African species of modern humans. Here we test the replacement theory in two peripheral areas far from Africa by examining the ancestry of early modern Australians and Central Europeans. Analysis of pairwise differences was used to determine if dual ancestry in local archaic populations and earlier modern populations from the Levant and/or Africa could be rejected. The data imply that both have a dual ancestry. The diversity of recent humans cannot result exclusively from a single Late Pleistocene dispersal.