bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetoconvection Dynamos and the Magnetic Fields of Io and Ganymede
Authors: Sarson G. R. , Jones C. A. , Zhang K. , Schubert G.
Published: July 2002

Data from the Galileo orbiter suggest that two of Jupiter’s moons, Io and Ganymede, have intrinsic magnetic fields. The magnetic field of Jupiter alters the nature of the magnetohydrodynamic processes generating these intrinsic fields. Such an imposed field allows appreciable internal fields to be generated in cases where convection cannot otherwise maintain a dynamo. The dipole moment of the internal field can then become aligned with the background field, as is observed for Io and Ganymede. Io might not have a self-sustained intrinsic field in the absence of the ambient jovian field; Ganymede is almost certainly operating as a dynamo in its own right.
Type Ia Supernovae: Their Origin and Possible Applications in Cosmology
Authors: Nomoto Ken’ichi , Iwamoto Koichi , Kishimoto Nobuhiro
Published: July 2002

Spectroscopic and photometric evidence indicates that Type Ia supernovae (SNe Ia) are the thermonuclear explosions of accreting white dwarfs. However, the progenitor binary systems and hydrodynamical models for SNe Ia are still controversial. The relatively uniform light curves and spectral evolution of SNe Ia have led to their use as a standard candle for determining cosmological parameters, such as the Hubble constant, the density parameter, and the cosmological constant. Recent progress includes the calibration of the absolute maximum brightness of SNe Ia with the Hubble Space Telescope, the reduction of the dispersion in the Hubble diagram through the use of the relation between the light curve shape and the maximum brightness of SNe Ia, and the discovery of many SNe Ia with high red shifts.
An Antagonist Decoy Receptor and a Death Domain-Containing Receptor for TRAIL
Authors: Pan Guohua , Ni Jian , Wei Ying-Fei , Yu Guo-liang , Gentz Reiner , Dixit Vishva M.
Published: July 2002

TRAIL, also called Apo2L, is a cytotoxic protein that induces apoptosis of many transformed cell lines but not of normal tissues, even though its death domain–containing receptor, DR4, is expressed on both cell types. An antagonist decoy receptor (designated as TRID for TRAIL receptor without an intracellular domain) that may explain the resistant phenotype of normal tissues was identified. TRID is a distinct gene product with an extracellular TRAIL-binding domain and a transmembrane domain but no intracellular signaling domain. TRID transcripts were detected in many normal human tissues but not in most cancer cell lines examined. Ectopic expression of TRID protected mammalian cells from TRAIL-induced apoptosis, which is consistent with a protective role. Another death domain–containing receptor for TRAIL (designated as death receptor–5), which preferentially engaged a FLICE (caspase-8)–related death protease, was also identified.
Enduring Cognitive Deficits and Cortical Dopamine Dysfunction in Monkeys After Long-Term Administration of Phencyclidine
Authors: Jentsch J. David , Redmond D. Eugene , Elsworth John D. , Taylor Jane R. , Youngren Kenneth D. , Roth Robert H.
Published: July 2002

The effects of the psychotomimetic drug phencyclidine on the neurochemistry and function of the prefrontal cortex in vervet monkeys were investigated. Monkeys treated with phencyclidine twice a day for 14 days displayed performance deficits on a task that was sensitive to prefrontal cortex function; the deficits were ameliorated by the atypical antipsychotic drug clozapine. Repeated exposure to phencyclidine caused a reduction in both basal and evoked dopamine utilization in the dorsolateral prefrontal cortex, a brain region that has long been associated with cognitive function. Behavioral deficits and decreased dopamine utilization remained after phencyclidine treatment was stopped, an indication that these effects were not simply due to direct drug effects. The data suggest that repeated administration of phencyclidine in monkeys may be useful for studying psychiatric disorders associated with cognitive dysfunction and dopamine hypofunction in the prefrontal cortex, particularly schizophrenia.
Thermophilic Fe(III)-Reducing Bacteria from the Deep Subsurface: The Evolutionary Implications
Authors: Liu Shi V. , Zhou Jizhong , Zhang Chuanlun , Cole David R. , Gajdarziska-Josifovska M. , Phelps Tommy J.
Published: July 2002

Thermophilic (45° to 75°C) bacteria that reduce amorphous Fe(III)-oxyhydroxide to magnetic iron oxides have been discovered in two geologically and hydrologically isolated Cretaceous- and Triassic-age sedimentary basins in the deep (>860 meters below land surface) terrestrial subsurface. Molecular analyses based on 16
S
ribosomal RNA (rRNA) gene sequences revealed that some of these bacteria represent an unrecognized phylogenetic group of dissimilatory Fe(III)-reducing bacteria. This discovery adds another dimension to the study of microbial Fe(III) reduction and biogenic magnetism. It also provides examples for understanding the history of Fe(III)-reducing microorganisms and for assessing possible roles of such microorganisms on hot primitive planets.
Time-Resolved Coherent Photoelectron Spectroscopy of Quantized Electronic States on Metal Surfaces
Authors: Höfer U. , Shumay I. L. , Reuß Ch. , Thomann U. , Wallauer W. , Fauster Th.
Published: July 2002

Time-resolved two-photon photoemission in combination with the coherent excitation of several quantum states was used to study the ultrafast electron dynamics of image-potential states on metal surfaces. For a (100) surface of copper, the spectroscopy of quantum beats made previously unresolved high-order states (quantum number
n
≥ 4) experimentally accessible. By exciting electrons close to the vacuum level, electron wave packets could be created and detected that described the quasi-classical periodic motion of weakly bound electrons. They traveled more than 200 Å away from the surface and oscillated back and forth with a period of 800 femtoseconds.
Proteolysis and DNA Replication: The
CDC34
Requirement in the
Xenopus
Egg Cell Cycle
Authors: Yew P. Renee , Kirschner Marc W.
Published: July 2002

The cell division cycle gene,
CDC34
, is required for ubiquitin-mediated degradation of G
1
regulators and cell cycle progression through the transition from G
1
to S phase in budding yeast. A
CDC34
requirement for S phase onset in higher eukaryotes has not been established. Studies of the simple embryonic cell cycle of
Xenopus laevis
eggs demonstrated that Cdc34p in a large molecular size complex was required in the initiation of DNA replication. Cdc34p appears to regulate the initiation function of Cdk2–cyclin E, perhaps through the degradation of the
Xenopus
cdk inhibitor, Xic1.
Identification of a Naturally Occurring Peroxidase-Lipoxygenase Fusion Protein
Authors: Koljak Reet , Boutaud Olivier , Shieh Bih-Hwa , Samel Nigulas , Brash Alan R.
Published: July 2002

A distant relative of catalase that is specialized for metabolism of a fatty acid hydroperoxide was identified. This heme peroxidase occurs in coral as part of a fusion protein, the other component of which is a lipoxygenase that forms the hydroperoxide substrate. The end product is an unstable epoxide (an allene oxide) that is a potential precursor of prostaglandin-like molecules. These results extend the known chemistry of catalase-like proteins and reveal a distinct type of enzymatic construct involved in the metabolism of polyunsaturated fatty acids.
Organics and Other Molecules in the Surfaces of Callisto and Ganymede
Authors: McCord T. B. , Carlson R. W. , Smythe W. D. , Hansen G. B. , Clark R. N. , Hibbitts C. A. , Fanale F. P. , Granahan J. C. , Segura M. , Matson D. L. , Johnson T. V. , Martin P. D.
Published: July 2002

Five absorption features are reported at wavelengths of 3.4, 3.88, 4.05, 4.25, and 4.57 micrometers in the surface materials of the Galilean satellites Callisto and Ganymede from analysis of reflectance spectra returned by the Galileo mission near-infrared mapping spectrometer. Candidate materials include CO
2
, organic materials (such as tholins containing C≡N and C-H), SO
2
, and compounds containing an SH-functional group; CO
2
, SO
2
, and perhaps cyanogen [(CN)
2
] may be present within the surface material itself as collections of a few molecules each. The spectra indicate that the primary surface constituents are water ice and hydrated minerals.
Quasi-Phase-Matched Third-Harmonic Generation in a Quasi-Periodic Optical Superlattice
Authors: Zhu Shi-ning , Zhu Yong-yuan , Ming Nai-ben
Published: July 2002

Quasi-periodic structure can be introduced into nonlinear optical materials such as LiTaO
3
crystals. Such structures were used for quasi–phase-matching second-harmonic generation. These materials are now shown to be able to couple second-harmonic generation and sum-frequency generation through quasi–phase-matching. The approach led to a direct third-harmonic generation with high efficiency through a coupled parametric process. The result verifies that high-order harmonics may be generated in a quadric nonlinear medium by a number of quasi–phase-matching processes, and therefore, exhibits a possible important application of quasi-periodic structure materials in nonlinear optics.
Isolation of an Intrinsic Precursor to Molecular Chemisorption
Authors: Brown David E. , Moffatt Douglas J. , Wolkow Robert A.
Published: July 2002

Over the past 70 years, numerous gas-surface adsorption studies have indicated the existence of a weakly bound, mobile intermediate that is a precursor to chemical bond formation. The direct observation and characterization of such a species are presented. Precursor and chemisorbed benzene on a silicon surface were clearly distinguished with the use of a tunable-temperature scanning tunneling microscope. Precursor decay to chemisorption was observed, allowing the salient features of the potential energy surface to be determined.
The Structure of GABPα/β: An ETS Domain- Ankyrin Repeat Heterodimer Bound to DNA
Authors: Batchelor Adrian H. , Piper Derek E. , de la Brousse Fabienne Charles , McKnight Steven L. , Wolberger Cynthia
Published: July 2002

GA-binding protein (GABP) is a transcriptional regulator composed of two structurally dissimilar subunits. The α subunit contains a DNA-binding domain that is a member of the ETS family, whereas the β subunit contains a series of ankyrin repeats. The crystal structure of a ternary complex containing a GABPα/β ETS domain–ankyrin repeat heterodimer bound to DNA was determined at 2.15 angstrom resolution. The structure shows how an ETS domain protein can recruit a partner protein using both the ETS domain and a carboxyl-terminal extension and provides a view of an extensive protein-protein interface formed by a set of ankyrin repeats. The structure also reveals how the GABPα ETS domain binds to its core GGA DNA-recognition motif.
c
-Axis Electrodynamics as Evidence for the Interlayer Theory of High-Temperature Superconductivity
Authors: Anderson Philip W.
Published: July 2002

In the interlayer theory of high-temperature superconductivity, the interlayer pair tunneling energy (similar to the Josephson or Lawrence-Doniach energy) is the motivation for superconductivity. This connection requires two experimentally verifiable identities: the coherent normal-state conductance must be smaller than the “Josephson” coupling energy, and the Josephson coupling energy must be equal to the condensation energy of the superconductor. The first condition is well satisfied in the only case that is relevant, (La,Sr)
2
CuO
4
, but the second condition has been questioned. It is satisfied for all dopings in (La,Sr)
2
CuO
4
and also in optimally doped Hg(Ba)
2
CuO
5
, which was measured recently, but seems to be strongly violated in measurements on single crystals of Tl
2
Ba
2
CuO
6
.
Time Scales in Atmospheric Chemistry: Coupled Perturbations to N
2
O, NO

y

, and O
3
Authors: Prather Michael J.
Published: July 2002

Nitrous oxide (N
2
O) is one of the top three greenhouse gases whose emissions may be brought under control through the Framework Convention on Climate Change. Current understanding of its global budget, including the balance of natural and anthropogenic sources, is largely based on the atmospheric losses calculated with chemical models. A representative one-dimensional model used here describes the photochemical coupling between N
2
O and stratospheric ozone (O
3
), which can easily be decomposed into its natural modes. The primary, longest lived mode describes most of the atmospheric perturbation due to anthropogenic N
2
O sources, and this pattern may be observable. The photolytic link between O
3
and N
2
O is identified as the mechanism causing this mode to decay 10 to 15 percent more rapidly than the N
2
O mean atmospheric lifetime, affecting the inference of anthropogenic sources.
Origin of Mountains on Io by Thrust Faulting and Large-Scale Mass Movements
Authors: Schenk Paul M. , Bulmer Mark H.
Published: July 2002

Voyager stereoimages of Euboea Montes, Io, indicate that this mountain formed when a large crustal block was uplifted 10.5 kilometers and tilted by approximately 6 degrees. Uplift triggered a massive slope failure on the northwest flank, forming one of the largest debris aprons in the solar system. This slope failure probably involved relatively unconsolidated layers totaling approximately 2 kilometers in thickness, overlying a rigid crust (or lithosphere) at least 11 kilometers thick. Mountain formation on Io may involve localized deep-rooted thrust faulting and block rotation, due to compression at depth induced during vertical recycling of Io's crust.
Protactinium-231 and Thorium-230 Abundances and High Scavenging Rates in the Western Arctic Ocean
Authors: Edmonds Henrietta N. , Moran S. Bradley , Hoff John A. , Smith John N. , Edwards R. Lawrence
Published: July 2002

The Canadian Basin of the Arctic Ocean, largely ice covered and isolated from deep contact with the more dynamic Eurasian Basin by the Lomonosov Ridge, has historically been considered an area of low productivity and particle flux and sluggish circulation. High-sensitivity mass-spectrometric measurements of the naturally occurring radionuclides protactinium-231 and thorium-230 in the deep Canada Basin and on the adjacent shelf indicate high particle fluxes and scavenging rates in this region. The thorium-232 data suggest that offshore advection of particulate material from the shelves contributes to scavenging of reactive materials in areas of permanent ice cover.
Identification of Non-Heme Diiron Proteins That Catalyze Triple Bond and Epoxy Group Formation
Authors: Lee Michael , Lenman Marit , Banaś Antoni , Bafor Maureen , Singh Surinder , Schweizer Michael , Nilsson Ralf , Liljenberg Conny , Dahlqvist Anders , Gummeson Per-Olov , Sjödahl Staffan , Green Allan , Stymne Sten
Published: July 2002

Acetylenic bonds are present in more than 600 naturally occurring compounds. Plant enzymes that catalyze the formation of the Δ12 acetylenic bond in 9-octadecen-12-ynoic acid and the Δ12 epoxy group in 12,13-epoxy-9-octadecenoic acid were characterized, and two genes, similar in sequence, were cloned. When these complementary DNAs were expressed in
Arabidopsis thaliana
, the content of acetylenic or epoxidated fatty acids in the seeds increased from 0 to 25 or 15 percent, respectively. Both enzymes have characteristics similar to the membrane proteins containing non–heme iron that have histidine-rich motifs.
Localized Reconnection in the Near Jovian Magnetotail
Authors: Russell C. T. , Khurana K. K. , Huddleston D. E. , Kivelson M. G.
Published: July 2002

The oppositely directed magnetic field in the jovian magnetic tail is expected eventually to reconnect across the current sheet, allowing plasma produced deep inside the magnetosphere near Io's orbit to escape in the antisolar direction down the tail. The Galileo spacecraft found localized regions of strong northward and southward field components beyond about 50 jovian radii in the postmidnight, predawn sector of the jovian magnetosphere. These pockets of vertical magnetic fields can be stronger than the surrounding magnetotail and magnetodisk fields. They may result from episodic reconnection of patches of the near jovian magnetotail.
Genetic Evaluation of Suspected Cases of Transient HIV-1 Infection of Infants
Authors: Frenkel Lisa M. , Mullins James I. , Learn Gerald H. , Manns-Arcuino Laura , Herring Belinda L. , Kalish Marcia L. , Steketee Richard W. , Thea Donald M. , Nichols Joan E. , Liu Shan-Lu , Harmache Abdallah , He Xi , Muthui David , Madan Anup , Hood Leroy , Haase Ashley T. , Zupancic Mary , Staskus Katherine , Wolinsky Steven , Krogstad Paul , Zhao JiaQi , Chen Irvin , Koup Richard , Ho David , Korber Bette , Apple Raymond J. , Coombs Robert W. , Pahwa Savita , Roberts Norbert J.
Published: July 2002

Detection of human immunodeficiency virus–type 1 (HIV-1) on only one or a few occasions in infants born to infected mothers has been interpreted to indicate that infection may be transient rather than persistent. Forty-two cases of suspected transient HIV-1 viremia among 1562 perinatally exposed seroreverting infants and one mother were reanalyzed. HIV-1
env
sequences were not found in specimens from 20; in specimens from 6, somatic genetic analysis revealed that specimens were mistakenly attributed to an infant; and in specimens from 17, phylogenetic analysis failed to demonstrate the expected linkage between the infant's and the mother's virus. These findings argue that transient HIV-1 infection, if it exists, will only rarely be satisfactorily documented.
Electrical Conductivity of Olivine, Wadsleyite, and Ringwoodite Under Upper-Mantle Conditions
Authors: Xu Yousheng , Poe Brent T. , Shankland Thomas J. , Rubie David C.
Published: July 2002

Geophysical models show that electrical conductivity in Earth's mantle rises about two orders of magnitude through the transition zone in the depth range 410 to 660 kilometers. Impedance measurements obtained on Mg
1.8
Fe
0.2
SiO
4
olivine, wadsleyite, and ringwoodite at up to 20 gigapascals and 1400°C show that the electrical conductivities of wadsleyite and ringwoodite are similar and are almost two orders of magnitude higher than that of olivine. A conductivity-depth profile to 660 kilometers, based on these laboratory data, shows a conductivity increase of almost two orders of magnitude across the 410-kilometer discontinuity; such a profile favors a two-layer model for the upper mantle. Activation enthalpies of 1.2 to 1.7 electron volts permit appreciable lateral variations of conductivity with lateral temperature variations.
The Influence of Vegetation-Atmosphere-Ocean Interaction on Climate During the Mid-Holocene
Authors: Ganopolski Andrey , Kubatzki Claudia , Claussen Martin , Brovkin Victor , Petoukhov Vladimir
Published: July 2002

Simulations with a synchronously coupled atmosphere–ocean–vegetation model show that changes in vegetation cover during the mid-Holocene, some 6000 years ago, modify and amplify the climate system response to an enhanced seasonal cycle of solar insolation in the Northern Hemisphere both directly (primarily through the changes in surface albedo) and indirectly (through changes in oceanic temperature, sea-ice cover, and oceanic circulation). The model results indicate strong synergistic effects of changes in vegetation cover, ocean temperature, and sea ice at boreal latitudes, but in the subtropics, the atmosphere–vegetation feedback is most important. Moreover, a reduction of the thermohaline circulation in the Atlantic Ocean leads to a warming of the Southern Hemisphere.
Functional Reconstitution of Ypt7p GTPase and a Purified Vacuole SNARE Complex
Authors: Sato Ken , Wickner William
Published: July 2002

Membrane trafficking has heretofore been studied with intact organelles. Here, fusion-competent proteoliposomes were reconstituted from a yeast vacuole detergent extract. Homotypic vacuole fusion requires many membrane proteins, including the Ypt7p guanosine triphosphatase and a “SNARE complex” with Vam3p and Nyv1p. Proteoliposomes from extracts immunodepleted of either Vam3p or Ypt7p could not fuse, but vesicles reconstituted from a mixture of these depleted extracts had restored fusion activity. Purified preassembled vacuolar SNARE complex, when reconstituted with a SNARE-depleted extract, was fully functional for fusion. Thus, solubilized integral membrane components can be reconstituted for priming, docking, and fusion steps of organelle trafficking.
Siderophore-Mediated Iron Transport: Crystal Structure of FhuA with Bound Lipopolysaccharide
Authors: Ferguson Andrew D. , Hofmann Eckhard , Coulton James W. , Diederichs Kay , Welte Wolfram
Published: July 2002

FhuA, the receptor for ferrichrome-iron in
Escherichia coli
, is a member of a family of integral outer membrane proteins, which, together with the energy-transducing protein TonB, mediate the active transport of ferric siderophores across the outer membrane of Gram-negative bacteria. The three-dimensional structure of FhuA is presented here in two conformations: with and without ferrichrome-iron at resolutions of 2.7 and 2.5 angstroms, respectively. FhuA is a β barrel composed of 22 antiparallel β strands. In contrast to the typical trimeric arrangement found in porins, FhuA is monomeric. Located within the β barrel is a structurally distinct domain, the “cork,” which mainly consists of a four-stranded β sheet and four short α helices. A single lipopolysaccharide molecule is noncovalently associated with the membrane-embedded region of the protein. Upon binding of ferrichrome-iron, conformational changes are transduced to the periplasmic pocket of FhuA, signaling the ligand-loaded status of the receptor. Sequence homologies and mutagenesis data are used to propose a structural mechanism for TonB-dependent siderophore-mediated transport across the outer membrane.
A Molecular Mechanism for Electrical Tuning of Cochlear Hair Cells
Authors: Ramanathan Krishnan , Michael Timothy H. , Jiang Guo-Jian , Hiel Hakim , Fuchs Paul A.
Published: July 2002

Cochlear frequency selectivity in lower vertebrates arises in part from electrical tuning intrinsic to the sensory hair cells. The resonant frequency is determined largely by the gating kinetics of calcium-activated potassium (BK) channels encoded by the
slo
gene. Alternative splicing of
slo
from chick cochlea generated kinetically distinct BK channels. Combination with accessory β subunits slowed the gating kinetics of α splice variants but preserved relative differences between them. In situ hybridization showed that the β subunit is preferentially expressed by low-frequency (apical) hair cells in the avian cochlea. Interaction of β with α splice variants could provide the kinetic range needed for electrical tuning of cochlear hair cells.
Argon-Lead Isotopic Correlation in Mid-Atlantic Ridge Basalts
Authors: Sarda Philippe , Moreira Manuel , Staudacher Thomas
Published: July 2002

Step-heating analyses for Mid-Atlantic Ridge glass samples show that maximum
40
Ar/
36
Ar values correlate with
206,207,208
Pb/
204
Pb. These correlations hold for the whole Atlantic Ocean and therefore are unlikely to result from shallow-level contamination processes. Instead, they are taken as mixing hyperbolae between the degassed-depleted upper mantle and a recycled component characterized by high
206
Pb/
204
Pb ratios (19 to 21) and low
40
Ar/
36
Ar ratios (300 to 1000). These relations imply that argon may also be a tracer of mantle recycling.
Chemical Etiology of Nucleic Acid Structure: Comparing Pentopyranosyl-(2'→4') Oligonucleotides with RNA
Authors: Beier M. , Reck F. , Wagner T. , Krishnamurthy R. , Eschenmoser A.
Published: July 2002

All four members of the family of pentopyranosyl-(2′→4′) oligonucleotide systems that contain β-ribo-, β-xylo-, α-lyxo-, or α-arabinopyranosyl units as repeating sugar building blocks are found to be much stronger Watson-Crick base-pairing systems than RNA. The α-arabinopyranosyl system is the strongest of all and in fact belongs to the strongest oligonucleotide base-pairing systems known. Whatever the chemical determinants by which nature selected RNA as a genetic system, maximization of base-pairing strengths within the domain of pentose-derived oligonucleotide systems was not the critical selection criterion.
Hydrogen Peroxide on the Surface of Europa
Authors: Carlson R. W. , Anderson M. S. , Johnson R. E. , Smythe W. D. , Hendrix A. R. , Barth C. A. , Soderblom L. A. , Hansen G. B. , McCord T. B. , Dalton J. B. , Clark R. N. , Shirley J. H. , Ocampo A. C. , Matson D. L.
Published: July 2002

Spatially resolved infrared and ultraviolet wavelength spectra of Europa's leading, anti-jovian quadrant observed from the Galileo spacecraft show absorption features resulting from hydrogen peroxide. Comparisons with laboratory measurements indicate surface hydrogen peroxide concentrations of about 0.13 percent, by number, relative to water ice. The inferred abundance is consistent with radiolytic production of hydrogen peroxide by intense energetic particle bombardment and demonstrates that Europa's surface chemistry is dominated by radiolysis.
Strongly Photonic Macroporous Gallium Phosphide Networks
Authors: P. Frank J. , Schuurmans  , Vanmaekelbergh Daniël , Lagemaat Jao van de , Lagendijk Ad
Published: July 2002

A photo-assisted electrochemical etching technique to fabricate macropores in single-crystalline gallium phosphide (GaP) with variable porosity has been developed. Scanning electron microscopy and x-ray diffraction experiments confirm that the material consists of three-dimensional, interconnected random networks with pore sizes of about 150 nanometers. Optical transmission measurements demonstrate that the nonabsorbing disordered structures strongly scatter light. The photonic strength is controlled by filling the pores with liquids of different refractive indices. Macroporous gallium phosphide filled with air has the highest scattering efficiency for visible light.
Dosage Compensation Proteins Targeted to X Chromosomes by a Determinant of Hermaphrodite Fate
Authors: Dawes Heather E. , Berlin Dorit S. , Lapidus Denise M. , Nusbaum Chad , Davis Tamara L. , Meyer Barbara J.
Published: July 2002

In many organisms, master control genes coordinately regulate sex-specific aspects of development. SDC-2 was shown to induce hermaphrodite sexual differentiation and activate X chromosome dosage compensation in
Caenorhabditis elegans
. To control these distinct processes, SDC-2 acts as a strong gene-specific repressor and a weaker chromosome-wide repressor. To initiate hermaphrodite development, SDC-2 associates with the promoter of the male sex-determining gene
her-1
to repress its transcription. To activate dosage compensation, SDC-2 triggers assembly of a specialized protein complex exclusively on hermaphrodite X chromosomes to reduce gene expression by half. SDC-2 can localize to X chromosomes without other components of the dosage compensation complex, suggesting that SDC-2 targets dosage compensation machinery to X chromosomes.
Middle Eocene Seawater pH and Atmospheric Carbon Dioxide Concentrations
Authors: Pearson Paul N. , Palmer Martin R.
Published: July 2002

The carbon dioxide content of the atmosphere [measured as the partial pressure of CO
2
(pCO
2
)] affects the content of the surface ocean, which in turn affects seawater pH. The boron isotope composition (δ
11
B) of contemporaneous planktonic foraminifera that calcified their tests at different water depths can be used to reconstruct the pH-depth profile of ancient seawater. Construction of a pH profile for the middle Eocene tropical Pacific Ocean shows that atmospheric pCO
2
was probably similar to modern concentrations or slightly higher.
A Role for the Proteasome in the Light Response of the Timeless Clock Protein
Authors: Naidoo Nirinjini , Song Wei , Hunter-Ensor Melissa , Sehgal Amita
Published: July 2002

The cyclic expression of the period (PER) and timeless (TIM) proteins is critical for the molecular circadian feedback loop in
Drosophila.
The entrainment by light of the circadian clock is mediated by a reduction in TIM levels. To elucidate the mechanism of this process, the sensitivity of TIM regulation by light was tested in an in vitro assay with inhibitors of candidate proteolytic pathways. The data suggested that TIM is degraded through a ubiquitin-proteasome mechanism. In addition, in cultures from third-instar larvae, TIM degradation was blocked specifically by inhibitors of proteasome activity. Degradation appeared to be preceded by tyrosine phosphorylation. Finally, TIM was ubiquitinated in response to light in cultured cells.
Past and Future Grounding-Line Retreat of the West Antarctic Ice Sheet
Authors: Conway H. , Hall B. L. , Denton G. H. , Gades A. M. , Waddington E. D.
Published: July 2002

The history of deglaciation of the West Antarctic Ice Sheet (WAIS) gives clues about its future. Southward grounding-line migration was dated past three locations in the Ross Sea Embayment. Results indicate that most recession occurred during the middle to late Holocene in the absence of substantial sea level or climate forcing. Current grounding-line retreat may reflect ongoing ice recession that has been under way since the early Holocene. If so, the WAIS could continue to retreat even in the absence of further external forcing.
A Short Fe-Fe Distance in Peroxodiferric Ferritin: Control of Fe Substrate Versus Cofactor Decay?
Authors: Hwang Jungwon , Krebs Carsten , Huynh Boi Hanh , Edmondson Dale E. , Theil Elizabeth C. , Penner-Hahn James E.
Published: July 2002

The reaction of oxygen with protein diiron sites is important in bioorganic syntheses and biomineralization. An unusually short Fe-Fe distance of 2.53 angstroms was found in the diiron (μ-1,2 peroxodiferric) intermediate that forms in the early steps of ferritin biomineralization. This distance suggests the presence of a unique triply bridged structure. The Fe-Fe distances in the μ-1,2 peroxodiferric complexes that were characterized previously are much longer (3.1 to 4.0 angstroms). The 2.53 angstrom Fe-Fe distance requires a small Fe-O-O angle (∼106° to 107°). This geometry should favor decay of the peroxodiferric complex by the release of H
2
O
2
and μ-oxo or μ-hydroxo diferric biomineral precursors rather than by oxidation of the organic substrate. Geometrical differences may thus explain how diiron sites can function either as a substrate (in ferritin biomineralization) or as a cofactor (in O
2
activation).
The Formation and Early Evolution of the Milky Way Galaxy
Authors: Buser Roland
Published: July 2002

Recent observations indicate that the Milky Way may have formed by aggregation of gas and stars from a reservoir of preexisting small galaxies in the local universe. The process probably began more than 12 billion years ago with material of different original angular momentum following two separate evolutionary lines, one into the slowly rotating halo and central bulge and the other into the rapidly rotating disk. The existence of distinct thick and thin disks shows that continuing mergers of satellite galaxies likely also determined the early evolution of the main structural component of the luminous Galaxy.
Influences of Dietary Uptake and Reactive Sulfides on Metal Bioavailability from Aquatic Sediments
Authors: Lee Byeong-Gweon , Griscom Sarah B. , Lee Jung-Suk , Choi Heesun J. , Koh Chul-Hwan , Luoma Samuel N. , Fisher Nicholas S.
Published: July 2002

Understanding how animals are exposed to the large repository of metal pollutants in aquatic sediments is complicated and is important in regulatory decisions. Experiments with four types of invertebrates showed that feeding behavior and dietary uptake control bioaccumulation of cadmium, silver, nickel, and zinc. Metal concentrations in animal tissue correlated with metal concentrations extracted from sediments, but not with metal in porewater, across a range of reactive sulfide concentrations, from 0.5 to 30 micromoles per gram. These results contradict the notion that metal bioavailability in sediments is controlled by geochemical equilibration of metals between porewater and reactive sulfides, a proposed basis for regulatory criteria for metals.
Nanometer-Size α-PbO
2
-Type TiO
2
in Garnet: A Thermobarometer for Ultrahigh-Pressure Metamorphism
Authors: Hwang Shyh-Lung , Shen Pouyan , Chu Hao-Tsu , Yui Tzen-Fu
Published: July 2002

A high-pressure phase of titanium dioxide (TiO
2
) with an α-PbO
2
–type structure has been identified in garnet of diamondiferous quartzofeldspathic rocks from the Saxonian Erzgebirge, Germany. Analytical electron microscopy indicates that this α-PbO
2
–type TiO
2
occurred as an epitaxial nanometer-thick slab between twinned rutile bicrystals. Given a V-shaped curve for the equilibrium phase boundary of α-PbO
2
–type TiO
2
to rutile, the stabilization pressure of α-PbO
2
–type TiO
2
should be 4 to 5 gigapascals at 900° to 1000°C. This suggests a burial of continental crustal rocks to depths of at least 130 kilometers. The α-PbO
2
–type TiO
2
may be a useful pressure and temperature indicator in the diamond stability field.
The Influence of Canadian Forest Fires on Pollutant Concentrations in the United States
Authors: Wotawa Gerhard , Trainer Michael
Published: July 2002

High carbon monoxide (CO) concentrations from uncertain origins occurred episodically in the southeastern United States during the summer of 1995. We show that these episodes were caused by large forest fires in Canada. Over a period of 2 weeks, these natural emissions increased CO concentrations in the southeastern United States as well as along the eastern seaboard, a region with one of the world's highest rates of anthropogenic emissions. Within the forest fire plumes, there were also high concentrations of ozone, volatile organic compounds, and aerosols. These results suggest that the impact of boreal forest fire emissions on air quality in the mid-latitudes of the Northern Hemisphere, where anthropogenic pollutant sources have been considered predominant, needs to be reevaluated.
Radar Observations of Asteroid 216 Kleopatra
Authors: Ostro Steven J. , Scott R. , Hudson  , Nolan Michael C. , Margot Jean-Luc , Scheeres Daniel J. , Campbell Donald B. , Magri Christopher , Giorgini Jon D. , Yeomans Donald K.
Published: July 2002

Radar observations of the main-belt, M-class asteroid 216 Kleopatra reveal a dumbbell-shaped object with overall dimensions of 217 kilometers by 94 kilometers by 81 kilometers (±25%). The asteroid's surface properties are consistent with a regolith having a metallic composition and a porosity comparable to that of lunar soil. Kleopatra's shape is probably the outcome of an exotic sequence of collisional events, and much of its interior may have an unconsolidated rubble-pile structure.
Structure and Function of a Human TAF
II
250 Double Bromodomain Module
Authors: Jacobson Raymond H. , Ladurner Andreas G. , King David S. , Tjian Robert
Published: July 2002

TFIID is a large multiprotein complex that initiates assembly of the transcription machinery. It is unclear how TFIID recognizes promoters in vivo when templates are nucleosome-bound. Here, it is shown that TAF
II
250, the largest subunit of TFIID, contains two tandem bromodomain modules that bind selectively to multiply acetylated histone H4 peptides. The 2.1 angstrom crystal structure of the double bromodomain reveals two side-by-side, four-helix bundles with a highly polarized surface charge distribution. Each bundle contains an

N
ɛ

-acetyllysine binding pocket at its center, which results in a structure ideally suited for recognition of diacetylated histone H4 tails. Thus, TFIID may be targeted to specific chromatin-bound promoters and may play a role in chromatin recognition.
Photon-Mediated Hybridization of Frenkel Excitons in Organic Semiconductor Microcavities
Authors: Lidzey David G. , Bradley Donal D. C. , Armitage Adam , Walker Steve , Skolnick Maurice S.
Published: July 2002

Coherent excitations of intricate assemblies of molecules play an important role in natural photosynthesis. Microcavities are wavelength-dimension artificial structures in which excitations can be made to couple through their mutual interactions with confined photon modes. Results for microcavities containing two spatially separated cyanine dyes are presented here, where simultaneous strong coupling of the excitations of the individual dyes to a single cavity mode leads to new eigenmodes, described as admixtures of all three states. These “hybrid” exciton-photon structures are of potential interest as model systems in which to study energy capture, storage, and transfer among coherently coupled molecular excitations.
Imaging Coherent Electron Flow from a Quantum Point Contact
Authors: Topinka M. A. , LeRoy B. J. , Shaw S. E. J. , Heller E. J. , Westervelt R. M. , Maranowski K. D. , Gossard A. C.
Published: July 2002

Scanning a charged tip above the two-dimensional electron gas inside a gallium arsenide/aluminum gallium arsenide nanostructure allows the coherent electron flow from the lowest quantized modes of a quantum point contact at liquid helium temperatures to be imaged. As the width of the quantum point contact is increased, its electrical conductance increases in quantized steps of 2
e
2
/
h
, where
e
is the electron charge and
h
is Planck's constant. The angular dependence of the electron flow on each step agrees with theory, and fringes separated by half the electron wavelength are observed. Placing the tip so that it interrupts the flow from particular modes of the quantum point contact causes a reduction in the conductance of those particular conduction channels below 2
e
2
/
h
without affecting other channels.
Neurodegeneration Prevented by Lentiviral Vector Delivery of GDNF in Primate Models of Parkinson's Disease
Authors: Kordower Jeffrey H. , Emborg Marina E. , Bloch Jocelyne , Ma Shuang Y. , Chu Yaping , Leventhal Liza , McBride Jodi , Chen Er-Yun , Palfi Stéphane , Roitberg Ben Zion , Brown W. Douglas , Holden James E. , Pyzalski Robert , Taylor Michael D. , Carvey Paul , Ling ZaoDung , Trono Didier , Hantraye Philippe , Déglon Nicole , Aebischer Patrick
Published: July 2002

Lentiviral delivery of glial cell line–derived neurotrophic factor (lenti-GDNF) was tested for its trophic effects upon degenerating nigrostriatal neurons in nonhuman primate models of Parkinson's disease (PD). We injected lenti-GDNF into the striatum and substantia nigra of nonlesioned aged rhesus monkeys or young adult rhesus monkeys treated 1 week prior with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Extensive GDNF expression with anterograde and retrograde transport was seen in all animals. In aged monkeys, lenti-GDNF augmented dopaminergic function. In MPTP-treated monkeys, lenti-GDNF reversed functional deficits and completely prevented nigrostriatal degeneration. Additionally, lenti-GDNF injections to intact rhesus monkeys revealed long-term gene expression (8 months). In MPTP-treated monkeys, lenti-GDNF treatment reversed motor deficits in a hand-reach task. These data indicate that GDNF delivery using a lentiviral vector system can prevent nigrostriatal degeneration and induce regeneration in primate models of PD and might be a viable therapeutic strategy for PD patients.
Aureusidin Synthase: A Polyphenol Oxidase Homolog Responsible for Flower Coloration
Authors: Nakayama T. , Yonekura-Sakakibara K. , Sato T. , Kikuchi S. , Fukui Y. , Fukuchi-Mizutani M. , Ueda T. , Nakao M. , Tanaka Y. , Kusumi T. , Nishino T.
Published: July 2002

Aurones are plant flavonoids that provide yellow color to the flowers of some popular ornamental plants, such as snapdragon and cosmos. In this study, we have identified an enzyme responsible for the synthesis of aurone from chalcones in the yellow snapdragon flower. The enzyme (aureusidin synthase) is a 39-kilodalton, copper-containing glycoprotein catalyzing the hydroxylation and/or oxidative cyclization of the precursor chalcones, 2′,4′,6′,4-tetrahydroxychalcone and 2′,4′,6′,3,4-pentahydroxychalcone. The complementary DNA encoding aureusidin synthase is expressed in the petals of aurone-containing varieties. DNA sequence analysis revealed that aureusidin synthase belongs to the plant polyphenol oxidase family, providing an unequivocal example of the function of the polyphenol oxidase homolog in plants, i.e., flower coloration.
Self-Mode-Locking of Quantum Cascade Lasers with Giant Ultrafast Optical Nonlinearities
Authors: Paiella Roberto , Capasso Federico , Gmachl Claire , Sivco Deborah L. , Baillargeon James N. , Hutchinson Albert L. , Cho Alfred Y. , Liu H. C.
Published: July 2002

We report on the generation of picosecond self–mode-locked pulses from midinfrared quantum cascade lasers, at wavelengths within the important molecular fingerprint region. These devices are based on intersubband electron transitions in semiconductor nanostructures, which are characterized by some of the largest optical nonlinearities observed in nature and by picosecond relaxation lifetimes. Our results are interpreted with a model in which one of these nonlinearities, the intensity-dependent refractive index of the lasing transition, creates a nonlinear waveguide where the optical losses decrease with increasing intensity. This favors the generation of ultrashort pulses, because of their larger instantaneous intensity relative to continuous-wave emission.
Formation of Sphalerite (ZnS) Deposits in Natural Biofilms of Sulfate-Reducing Bacteria
Authors: Labrenz Matthias , Druschel Gregory K. , Thomsen-Ebert Tamara , Gilbert Benjamin , Welch Susan A. , Kemner Kenneth M. , Logan Graham A. , Summons Roger E. , Stasio Gelsomina De , Bond Philip L. , Lai Barry , Kelly Shelly D. , Banfield Jillian F.
Published: July 2002

Abundant, micrometer-scale, spherical aggregates of 2- to 5-nanometer-diameter sphalerite (ZnS) particles formed within natural biofilms dominated by relatively aerotolerant sulfate-reducing bacteria of the family
Desulfobacteriaceae.
The biofilm zinc concentration is about 10
6
times that of associated groundwater (0.09 to 1.1 parts per million zinc). Sphalerite also concentrates arsenic (0.01 weight %) and selenium (0.004 weight %). The almost monomineralic product results from buffering of sulfide concentrations at low values by sphalerite precipitation. These results show how microbes control metal concentrations in groundwater- and wetland-based remediation systems and suggest biological routes for formation of some low-temperature ZnS deposits.
Chromatin Docking and Exchange Activity Enhancement of RCC1 by Histones H2A and H2B
Authors: Nemergut Michael E. , Mizzen Craig A. , Stukenberg Todd , Allis C. David , Macara Ian G.
Published: July 2002

The Ran guanosine triphosphatase (GTPase) controls nucleocytoplasmic transport, mitotic spindle formation, and nuclear envelope assembly. These functions rely on the association of the Ran-specific exchange factor, RCC1 (regulator of chromosome condensation 1), with chromatin. We find that RCC1 binds directly to mononucleosomes and to histones H2A and H2B. RCC1 utilizes these histones to bind
Xenopus
sperm chromatin, and the binding of RCC1 to nucleosomes or histones stimulates the catalytic activity of RCC1. We propose that the docking of RCC1 to H2A/H2B establishes the polarity of the Ran-GTP gradient that drives nuclear envelope assembly, nuclear transport, and other nuclear events.
Clinical Correlates of Antifungal Macrodilution Susceptibility Test Results for Non-AIDS Patients with Severe
Candida
Infections Treated with Fluconazole
Authors: Lee Sai-Cheong , Fung Chang-Phone , Huang Jen-Seng , Tsai Chi-Jen , Chen Kuo-Su , Chen Huang-Yang , Lee Ning , See Lai-Chu , Shieh Wen-Ben
Published: July 2002

Although the clinical correlates of the reference antifungal susceptibility test results in hematogenous and deep-seated
Candida
infection are still controversial, we evaluated the clinical correlates of this test in deep-seated
Candida
infections in non-AIDS patients. Thirty-two non-AIDS patients with hematogenous or deep-seated
Candida
infections were treated with intravenous fluconazole (400 mg a day), and the clinical outcomes were evaluated. Coexisting bacterial infections were treated with appropriate antibiotics, superinfection or reinfection was excluded, inadequate fluconazole therapy was avoided, and essential surgical intervention was performed. The MICs of fluconazole for these 32
Candida
isolates were determined according to the M27-A procedure approved by the National Committee on Clinical Laboratory Standards. MICs were interpreted as susceptible (≤8 μg/ml), dose-dependent susceptible (16 to 32 μg/ml), and resistant (≥64 μg/ml) according to the criteria of the M27-A standard. The success rates were 79% (19 of 24; 95% confidence interval [CI], 59 to 93%) in the susceptible category, 66% (4 of 6; 95% CI, 19 to 95%) in the dose-dependent susceptible category, and 0% (0 of 2; 95% CI, 0 to 84%) in the resistant category. We conclude that the clinical correlation of the reference antifungal susceptibility test results is high in hematogenous and deep-seated
Candida
infections.
Engineering the Specificity of Antibacterial Fluoroquinolones: Benzenesulfonamide Modifications at C-7 of Ciprofloxacin Change Its Primary Target in
Streptococcus pneumoniae
from Topoisomerase IV to Gyrase
Authors: Alovero Fabiana L. , Pan Xiao-Su , Morris Julia E. , Manzo Ruben H. , Fisher L. Mark
Published: July 2002

We have examined the antipneumococcal mechanisms of a series of novel fluoroquinolones that are identical to ciprofloxacin except for the addition of a benzenesulfonylamido group to the C-7 piperazinyl ring. A number of these derivatives displayed enhanced activity against
Streptococcus pneumoniae
strain 7785, including compound NSFQ-105, bearing a 4-(4-aminophenylsulfonyl)-1-piperazinyl group at C-7, which exhibited an MIC of 0.06 to 0.125 μg/ml compared with a ciprofloxacin MIC of 1 μg/ml. Several complementary approaches established that unlike the case for ciprofloxacin (which targets topoisomerase IV), the increased potency of NSFQ-105 was associated with a target preference for gyrase: (i)
parC
mutants of strain 7785 that were resistant to ciprofloxacin remained susceptible to NSFQ-105, whereas by contrast, mutants bearing a quinolone resistance mutation in
gyrA
were four- to eightfold more resistant to NSFQ-105 (MIC of 0.5 μg/ml) but susceptible to ciprofloxacin; (ii) NSFQ-105 selected first-step
gyrA
mutants (MICs of 0.5 μg/ml) encoding Ser-81-to-Phe or -Tyr mutations, whereas ciprofloxacin selects
parC
mutants; and (iii) NSFQ-105 was at least eightfold more effective than ciprofloxacin at inhibiting DNA supercoiling by
S. pneumoniae
gyrase in vitro but was fourfold less active against topoisomerase IV. These data show unequivocally that the C-7 substituent determines not only the potency but also the target preference of fluoroquinolones. The importance of the C-7 substituent in drug-enzyme contacts demonstrated here supports one key postulate of the Shen model of quinolone action.
The Macrolide-Lincosamide-Streptogramin B Resistance Determinant from
Clostridium difficile
630 Contains Two
erm
(B) Genes
Authors: Farrow Kylie A. , Lyras Dena , Rood Julian I.
Published: July 2002

The ErmB macrolide-lincosamide-streptogramin B (MLS) resistance determinant from
Clostridium difficile
630 contains two copies of an
erm
(B) gene, separated by a 1.34-kb direct repeat also found in an Erm(B) determinant from
Clostridium perfringens
. In addition, both
erm
(B) genes are flanked by variants of the direct repeat sequence. This genetic arrangement is novel for an ErmB MLS resistance determinant.
In Vitro Activity of ABT-773, a New Ketolide, against Recent Clinical Isolates of
Streptococcus pneumoniae
,
Haemophilus influenzae
, and
Moraxella catarrhalis
Authors: Brueggemann Angela B. , Doern Gary V. , Huynh Holly K. , Wingert Elizabeth M. , Rhomberg Paul R.
Published: July 2002

The in vitro activity of ABT-773 was evaluated against
Streptococcus pneumoniae
,
Haemophilus influenzae
, and
Moraxella catarrhalis
isolates. ABT-773 was the most active antimicrobial tested against
S. pneumoniae
. ABT-773 and azithromycin were equivalent in activity against
H. influenzae
and
M. catarrhalis
and more active than either clarithromycin or erythromycin.