bluuebunny/crossref_metadata_2025 huggingface dataset:
The Hin Invertasome: Protein-Mediated Joining of Distant Recombination Sites at the Enhancer
Authors: Heichman Karen A. , Johnson Reid C.
Published: October 2006

The Hin protein binds to two cis-acting recombination sites and catalyzes a site-specific DNA inversion reaction that regulates the expression of flagellin genes in
Salmonella
. In addition to the Hin protein and the two recombination sites that flank the invertible segment, a third cis-acting recombinational enhancer sequence and the Fis protein, which binds to two sites within the enhancer, are required for efficient recombination. Intermediates of this reaction were trapped during DNA strand cleavage and analyzed by gel electrophoresis and electron microscopy in order to determine their structure and composition. The analyses demonstrate that the recombination sites are assembled at the enhancer into a complex nucleoprotein structure (termed the invertasome) with the looping of the three segments of intervening DNA. Antibody studies indicated that Fis physically interacts with Hin and that both proteins are intimately associated with the invertasome. In order to achieve this protein-protein interaction and assemble the invertasome, the substrate DNA must be supercoiled.
Primary Sulfates in Atmospheric Sulfates: Estimation by Oxygen Isotope Ratio Measurements
Authors: Holt Ben D. , Kumar Romesh , Cunningham Paul T.
Published: October 2006

The relative amounts of primary and secondary sulfates in atmospheric aerosols and precipitation can be estimated from measurements of the stable oxygen isotope ratios. The oxygen-18 content of sulfates formed in power plant stack gases before emission into the atmosphere is significantly higher than that of sulfates formed from sulfur dioxide after emission. Results show that 20 to 30 percent of the sulfates in rain and snow at Argonne, Illinois, are of primary origin.
Oak Leaf Quality Declines in Response to Defoliation by Gypsy Moth Larvae
Authors: Schultz Jack C. , Baldwin Ian T.
Published: October 2006

Leaves of red oak trees that had been defoliated by gypsy moth larvae during the previous year and again during the period of the study had higher values of tanning coefficients, total phenolics, hydrolyzable and condensed tannins, dry matter contents, and toughness than did leaves of undamaged trees. These changes may influence larval growth and alter the course of further outbreaks.
Advection of Pore Fluids Through Sediments in the Equatorial East Pacific
Authors: Sayles Frederick L. , Jenkins William J.
Published: October 2006

Measurements of the ratio of helium-4 to helium-3 and of calcium ion in the pore waters of sediments at two locations in the eastern equatorial Pacific indicate that solution advection is occurring through the sediments. Both the helium ratio and the calcium ion profile yield velocity values for advective flow of about 20 centimeters per year. Mass balance constraints are also consistent with the interpretation presented. Flow appears to be occurring through relatively thick sediments, on the order of 300 meters.
Inorganic Pyrophosphate: Energy Source for Sulfate-Reducing Bacteria of the Genus
Desulfotomaculum
Authors: Liu Chi-Li , Hart Nancy , Peck Harry D.
Published: October 2006

Sulfate-reducing bacteria belonging to the genus
Desulfotomaculum
utilized inorganic pyrophosphate as a source of energy for growth in the presence of fixed carbon (acetate and yeast extract) and sulfate. Pyrophosphate does not support the growth of
Desulfovibrio
under the same growth conditions. Over a limited range of concentrations, growth is proportional to pyrophosphate, and extracts of bacteria grown on pyrophosphate medium have enzymatic activities similar to extracts prepared from bacteria grown on medium containing lactate plus sulfate. The variety of cell types observed in crude anaerobic pyrophosphate-enrichment cultures from a marine environment suggests that this unique type of energy metabolism is not restricted to the sulfate-reducing bacteria of the genus
Desulfotomaculum
.
Acceleration of Uranium at the Bevalac
Authors: Alonso J. R. , Avery R. T. , Elioff T. , Force R. J. , Grunder H. A. , Lancaster H. D. , Lofgren E. J. , Meneghetti J. R. , Selph F. B. , Stevenson R. R. , Yourd R. B.
Published: October 2006

Recent upgrading projects have extended the mass range of particles that can be accelerated at the Bevalac to include any element of the periodic table to energies above 1 billion electron volts per atomic mass unit. This capability was verified on 11 May 1982 with the production of a uranium beam at 147.7 million electron volts per atomic mass unit.
Colony Defense by Africanized and European Honey Bees
Authors: Collins Anita M. , Rinderer Thomas E. , Harbo John R. , Bolten Alan B.
Published: October 2006

Africanized and European honey bee (
Apis mellifera
) populations showed quantitative differences in colony defensive behavior. Africanized bees responded faster and in much larger numbers than European honey bees and produced 8.2 and 5.9 times as many stings during two different experiments. Times to react to alarming stimuli were negatively correlated with the number of bees responding and to the total number of stings. The number of bees responding was significantly correlated to the total number of stings only for the Africanized population.
Iron-Containing Cells in the Honey Bee (
Apis mellifera
)
Authors: Kuterbach Deborah A. , Walcott Benjamin , Reeder Richard J. , Frankel Richard B.
Published: October 2006

Honey bees are sensitive to earth strength magnetic fields and are reported to contain magnetite (Fe
3
O
4
) in their abdomens. We report bands of cells around each abdominal segment that contain numerous electron-opaque, iron-containing granules. The iron is principally in the form of hydrous iron oxides.
No Specific Recognition of Leader Peptide by SecB, a Chaperone Involved in Protein Export
Authors: Randall L. L. , Topping T. B. , Hardy S. J. S.
Published: October 2006

Most proteins destined for export from
Escherichia coli
are made as precursors containing amino-terminal leader sequences that are essential for export and that are removed during the process. The initial step in export of a subset of proteins, which includes maltose-binding protein, is binding of the precursor by the molecular chaperone SecB. This work shows directly that SecB binds with high affinity to unfolded maltose-binding protein but does not specifically recognize and bind the leader. Rather, the leader modulates folding to expose elements in the remainder of the polypeptide that are recognized by SecB.
Cell Interactions in the Sea Urchin Embryo Studied by Fluorescence Photoablation
Authors: Ettensohn Charles A.
Published: October 2006

In many organisms, interactions between cells play a critical role in the specification of cell fates. In the sea urchin embryo, primary mesenchyme cells (PMCs) regulate the developmental program of a subpopulation of secondary mesenchyme cells (SMCs). The timing of this cell interaction was analyzed by means of a fluorescence photoablation technique, which was used to specifically ablate PMCs at various stages of development. In addition, the PMCs were microinjected into PMC-depleted recipient embryos at different developmental stages and their effect on SMC fate was examined. The critical interaction between PMCs and SMCs was brief and took place late in gastrulation. Before that time, SMCs were insensitive to the suppressive signals transmitted by the PMCs.
Net Primary Productivity in Coral Reef Sponges
Authors: Wilkinson Clive R.
Published: October 2006

Nine of the ten most common sponge species on the fore-reef slope of Davies Reef(Great Barrier Reef) contain symbiotic cyanobacteria. Six of the ten are net primary producers, with three times more oxygen produced by photosynthesis than is consumed during respiration. Light interception is enhanced by morphological flattening, thereby increasing the potential for phototrophic nutrition, a factor crucial in the ecology of most sessile coral reef invertebrates.
The Mass-Independent Fractionation of Oxygen: A Novel Isotope Effect and Its Possible Cosmochemical Implications
Authors: Thiemens Mark H. , Heidenreich John E.
Published: October 2006

Experimental evidence is presented which demonstrates a chemically produced, mass-independent isotopic fractionation of oxygen. The effect is thought to result from self-shielding by the major isotopic species
16
O
2
, but other possible mechanisms such as molecular symmetry cannot be ruled out. In a three-isotope plot, the experimentally produced fractionation line is essentially equal in slope to the observed carbonaceous chondrite mixing line. The implications for the early history of the solar system are discussed.
Spasmodic Tremor and Possible Magma Injection in Long Valley Caldera, Eastern California
Authors: Ryall Alan , Ryall Floriana
Published: October 2006

Intensive microearthquake swarms with the appearance of volcanic tremor have been observed in the southwest part of Long Valley caldera, southeastern California. This activity, possibly associated with magma injection, began 6 weeks after several strong (magnitude 6+) earthquakes in an area south of the caldera and has continued sporadically to the present time. The earthquake sequence and magmatic activity are part of a broad increase in tectonic activity in a 15,000-square-kilometer region surrounding the "White Mountains seismic gap," an area with high potential for the next major earthquake in the western Great Basin.
Bacteria-Free Sea Urchin Larvae: Selective Uptake of Neutral Amino Acids from Seawater
Authors: Manahan Donal T. , Davis James P. , Stephens Grover C.
Published: October 2006

Bacteria-free suspensions of larvae of
Strongylocentrotus purpuratus
(Stimpson) were prepared without the use of antibiotics. Net rates of removal of 18 amino acids, each supplied at 125 nanomoles per liter, and the appearance of ammonia were measured by high-performance liquid chromatography. Taurine and acidic and basic amino acids were not taken up. Removal of neutral amino acids from the medium occurred at rates adequate to contribute to the carbon and nitrogen balance of the larvae at ecologically relevant substrate concentrations.
Design, Activity, and 2.8 Å Crystal Structure of a
C
2
Symmetric Inhibitor Complexed to HIV-1 Protease
Authors: Erickson John , Neidhart David J. , VanDrie John , Kempf Dale J. , Wang Xiu Chun , Norbeck Daniel W. , Plattner Jacob J. , Rittenhouse Judith W. , Turon Mary , Wideburg Norman , Kohlbrenner William E. , Simmer Robert , Helfrich Rosalind , Paul Deborah A. , Knigge Mark
Published: October 2006

A two-fold (
C
2
) symmetric inhibitor of the protease of human immunodeficiency virus type-1 (HIV-1) has been designed on the basis of the three-dimensional symmetry of the enzyme active site. The symmetric molecule inhibited both protease activity and acute HIV-1 infection in vitro, was at least 10,000-fold more potent against HIV-1 protease than against related enzymes, and appeared to be stable to degradative enzymes. The 2.8 angstrom crystal structure of the inhibitor-enzyme complex demonstrated that the inhibitor binds to the enzyme in a highly symmetric fashion.
Enzymatic Coupling of Cholesterol Intermediates to a Mating Pheromone Precursor and to the Ras Protein
Authors: Schafer William R. , Trueblood Cynthia Evans , Yang Chi-Ching , Mayer Matthias P. , Rosenberg Steven , Poulter C. Dale , Kim Sung-Hou , Rine Jasper
Published: October 2006

The post-translational processing of the yeast a-mating pheromone precursor, Ras proteins, nuclear lamins, and some subunits of trimeric G proteins requires a set of complex modifications at their carboxyl termini. This processing includes three steps: prenylation of a cysteine residue, proteolytic processing, and carboxymethylation. In the yeast
Saccharomyces cerevisiae
, the product of the
DPR1-RAM1
gene participates in this type of processing. Through the use of an in vitro assay with peptide substrates modeled after a presumptive a-mating pheromone precursor, it was discovered that mutations in
DPR1-RAM1
cause a defect in the prenylation reaction. It was further shown that
DPR1-RAM1
encodes an essential and limiting component of a protein prenyltransferase. These studies also implied a fixed order of the three processing steps shared by prenylated proteins: prenylation, proteolysis, then carboxymethylation. Because the yeast protein prenyltransferase could also prenylate human H-ras p21 precursor, the human DPR1-RAM1 analogue may be a useful target for anticancer chemotherapy.
Population Density of Tropical Forest Frogs: Relation to Retreat Sites
Authors: Stewart Margaret M. , Pough F. Harvey
Published: October 2006

The forest frog
Eleutherodactylus coqui
defends specific sites for retreats and nests in the Luquillo Forest, Puerto Rico. The hypothesis that shortages of nest and retreat sites limit population size was tested by placing 100 bamboo frog houses in plots measuring 100 square meters in areas of high frog density. These new sites were readily adopted by adult frogs. After one year, experimental plots had significantly more nests and frogs of all sizes than did control plots.
Thermoelectric Energy Conversion with Solid Electrolytes
Authors: Cole Terry
Published: October 2006

The alkali metal thermoelectric converter (AMTEC) is a device for the direct conversion of heat to electrical energy. The sodium ion conductor beta′′-alumina is used to form a high-temperature regenerative concentration cell for elemental sodium. An AMTEC of mature design should have an efficiency of 20 to 40 percent, a power density of 0.5 kilowatt per kilogram or more, no moving parts, low maintenance requirements, high durability, and efficiency independent of size. It should be usable with high-temperature combustion, nuclear, or solar heat sources. Experiments have demonstrated the feasibility of the AMTEC and confirmed the theoretical analysis of the device. A wide range of applications from aerospace power to utility power plants appears possible.
In Vitro Reconstruction of the Respiratory Central Pattern Generator of the Mollusk
Lymnaea
Authors: Syed N. I. , Bulloch A. G. , Lukowiak K.
Published: October 2006

Most rhythmic behaviors such as respiration, locomotion, and feeding are under the control of networks of neurons in the central nervous system known as central pattern generators (CPGs). The respiratory rhythm of the pond snail
Lymnaea stagnalis
is a relatively simple, CPG-based behavior for which the underlying neural elements have been identified. A three-neuron network capable of generating the respiratory rhythm of this air-breathing mollusk has been reconstructed in culture. The intrinsic and network properties of this neural ensemble have been studied, and the mechanism of postinhibitory rebound excitation was found to be important for the rhythm generation. This in vitro model system enables a better understanding of the neural basis of rhythm generation.
Seep Oil and Gas in Gulf of Mexico Slope Sediment
Authors: Anderson R. K. , Scalan R. S. , Parker P. L. , Behrens E. W.
Published: October 2006

Concentrations in Gulf of Mexico slope sediment of material soluble in methanol and benzene as high as 4.5 percent are shown to be attributable to biodegraded petroleum. Associated carbonate deposits and organic sulfur are the products of the microbial oxidation of petroleum and sulfate reduction. The results of chemical and carbon isotope analyses indicate that high concentrations of hydrocarbon gases, from methane to pentane, are petroleum rather than microbiologically derived. These hydrocarbons, believed to have been produced thermally at depth, probably reached the surface through faults and fractures associated with salt diapirs.
Volcanic Aerosols and Lunar Eclipses
Authors: Keen Richard A.
Published: October 2006

The moon is visible during total lunar eclipses due to sunlight refracted into the earth's shadow by the atmosphere. Stratospheric aerosols can profoundly affect the brightness of the eclipsed moon. Observed brightnesses of 21 lunar eclipses during 1960-1982 are compared with theoretical calculations based on refraction by an aerosol-free atmosphere to yield globally averaged aerosol optical depths. Results indicate the global aerosol loading from the 1982 eruption of El Chichón is similar in magnitude to that from the 1963 Agung eruption.
Van der Waals Surfaces in Molecular Modeling: Implementation with Real-Time Computer Graphics
Authors: Bash Paul A. , Pattabiraman Nagarajan , Huang Conrad , Ferrin Thomas E. , Langridge Robert
Published: October 2006

A method is described for generating van der Waals molecular surfaces with a real-time interactive calligraphic color display system. These surfaces maintain their proper representation during bond rotation and global transformations, and an interior atom removal method yields a comprehensible picture of the molecular surface for large molecules. Both algorithms are faster than previous methods. This combination provides a powerful tool for real-time interactive molecular modeling.
Free-Radical Carbon-Carbon Bond Formation in Organic Synthesis
Authors: Hart David J.
Published: October 2006

Organic chemists have begun to use intra- and intermolecular free-radical addition reactions to develop useful synthetic transformations. Carboncentered radicals can form bonds with electron-rich or electron-deficient alkenes, allenes, and acetylenes. Radical addition reactions can also be used to construct hindered carbon-carbon bonds. These characteristics, as well as the large number of functional groups that tolerate free-radical conditions contribute to the importance of such reactions in organic synthesis.
Sulfur Dioxide: Episodic Injection Shows Evidence for Active Venus Volcanism
Authors: Esposito Larry W.
Published: October 2006

Pioneer Venus ultraviolet spectra from the first 5 years of operation show a decline (by more than a factor of 10) in sulfur dioxide abundance at the cloud tops and in the amount of submicron haze above the clouds. At the time of the Pioneer Venus encounter, the values for both parameters greatly exceeded earlier upper limits. However, Venus had a similar appearance in the late 1950's, implying the episodic injection of sulfur dioxide possibly caused by episodic volcanism. The amount of haze in the Venus middle atmosphere is about ten times that found in Earth's stratosphere after the most recent major volcanic eruptions, and the thermal energy required for this injection on Venus is greater by about an order of magnitude than the largest of these recent Earth eruptions and about as large as the Krakatoa eruption of 1883. The episodic behavior of sulfur dioxide implies that steady-state models of the chemistry and dynamics of cloud-top regions may be of limited use.
Active Aerial Dispersal of Minute Wingless Arthropods: Exploitation of Boundary-Layer Velocity Gradients
Authors: Washburn Jan O. , Washburn Libe
Published: October 2006

The wingless first instars of the coccid
Pulvinariella mesembryanthemi
exhibit active aerial dispersal behavior by standing on their hind legs. This behavior is an age-specific response to the ambient wind velocity by which the instars are able to capitalize on air velocity gradients in the thin boundary layer surrounding the host plant substrate. This dispersal tactic may be a convergent evolutionary strategy for many minute terrestrial arthropods.
Biomass of Tropical Forests: A New Estimate Based on Forest Volumes
Authors: Brown Sandra , Lugo Ariel E.
Published: October 2006

Recent assessments of areas of different tropical forest types and their corresponding stand volumes were used to calculate the biomass densities and total biomass of tropical forests. Total biomass was estimated at 205 × 10
9
tons, and weighted biomass densities for undisturbed closed and open broadleaf forests were 176 and 61 tons per hectare, respectively. These values are considerably lower than those previously reported and raise questions about the role of the terrestrial biota in the global carbon budget.
X-ray Laue Diffraction from Protein Crystals
Authors: Moffat Keith , Szebenyi Doletha , Bilderback Donald
Published: October 2006

In conventional x-ray diffraction experiments on single crystals, essentially monochromatic x-rays are used. If polychromatic x-rays derived from a synchrotron radiation spectrum are used, they generate a Laue diffraction pattern. Laue patterns from single crystals of macromolecules can be obtained in less than 1 second, and significant radiation damage does not occur over the course of an exposure. Integrated intensities are obtained without rotation of the crystal, and individual structure factors may be extracted for most reflections. The Laue technique thus offers advantages for the recording of diffraction patterns from short-lived structural intermediates; that is, for time-resolved crystallography.
Digitalis Genin Activity: Side-Group Carbonyl Oxygen Position Is a Major Determinant
Authors: Fullerton Dwight S. , Yoshioka Kouichi , Rohrer Douglas C. , From Arthur H. L. , Ahmed Khalil
Published: October 2006

The Na
+
, K
+
-adenosine triphosphatase-inhibiting activity of digitalis genins and their analogs is a function of side-group carbonyl (C = O) oxygen position. For each 2.2 angstroms that this oxygen is displaced from its position in digitoxigenin, activity drops by one order of magnitude. This quantitative relation resolves previously proposed models which have attempted to describe the molecular basis of genin activity. A multidisciplinary (crystallographic, conformational energy, synthetic, biological) approach to structure-activity relations is described.
Thyrotropin-Releasing Hormone Selectively Depresses Glutamate Excitation of Cerebral Cortical Neurons
Authors: Renaud L. P. , Blume H. W. , Pittman Q. J. , Lamour Y. , Tan A. T.
Published: October 2006

The microiontophoretic application of thyrotropin-releasing hormone causes a selective reduction in neuronal excitation evoked by L-glutamate but not by acetylcholine in rat cerebral cortex. Thyrotropin-releasing hormone has no influence on the activity of acetylcholinesterase or on choline uptake and release from cerebral synaptosomes. This evidence for a selective interaction between a centrally acting peptide and an excitatory amino acid neurotransmitter may indicate a specific locus of thyrotropin-releasing hormone action at glutamate-activated receptor sites.
Cation Diffusion in Plagioclase Feldspar
Authors: Morse S. A.
Published: October 2006

Steep compositional gradients in igneous plagioclase feldspar from slowly cooled intrusive bodies imply a maximum value of the intracrystalline diffusion coefficient for NaSi ⇄ CaAl exchange, D
max
∼10
-20
centimeters squared per second for temperatures in the range 1250° to 1000°C. Millimeter-sized grains cannot be homogenized in all geologic time; hence reactive equilibrium crystallization of plagioclase from the melt does not occur in dry systems.
Periodic Interfacial Precipitation in Polymer Films
Authors: Mueller Karl F.
Published: October 2006

Interfacial precipitation of silver halides in water-swollen polymer films occurred in complex, multilayered patterns if the concentrations of counterdiffusing reactants were unequal or decreased at different rates. Development of the rapidly forming Liesegang rings, which extend the phenomenon of periodic precipitation to the submicrometer range, is attributable to the combined effect of a moving reaction zone and periodic immobilization of colloidal silver halide.
Magnetic Cristobalite (?): A Possible New Magnetic Phase Produced by the Thermal Decomposition of Nontronite
Authors: Moskowitz Bruce M. , Hargraves Robert B.
Published: October 2006

Prolonged heat treatment (> 1 hour) of nontronite (an iron-rich smectite clay) at 900° to 1000°C produces a phase with some unusual magnetic properties. This new phase has a Curie temperature of 200° to 220°C, extremely high remanent coercivities in excess of 800 milliteslas, and a room-temperature coercivity dependent on the magnitude of the applied field during previous thermomagnetic cycling from above 220°C. X-ray and magnetic analyses suggest that an iron-substituted cristobalite could be responsible, in part, for these observations. Formation of this magnetic cristobalite, however, may require topotactic growth from a smectite precursor.
Dissociation of gp120 from HIV-1 Virions Induced by Soluble CD4
Authors: Moore John P. , McKeating Jane A. , Weiss Robin A. , Sattentau Quentin J.
Published: October 2006

The CD4 antigen is the high affinity cellular receptor for the human immunodeficiency virus type-1 (HIV-1). Binding of recombinant soluble CD4 (sCD4) or the purified V1 domain of sCD4 to the surface glycoprotein gp120 on virions resulted in rapid dissociation of gp120 from its complex with the transmembrane glycoprotein gp41. This may represent the initial stage in virus-cell and cell-cell fusion. Shedding of gp120 from virions induced by sCD4 may also contribute to the mechanism by which these soluble receptor molecules neutralize HIV-1.
Gas-Phase Ion Chemistry
Authors: Comita Paul B. , Brauman John I.
Published: October 2006

Progress has been made in the understanding of potential energy surfaces for unimolecular ion dissociations and ion-molecule reactions. With recent advances in instrumentation, many new techniques have been developed to generate and study ions, ion-molecule complexes, and large ionic clusters. Developments in ion spectroscopy have enabled considerable advances to be made in the determination of ion structures.
Diploid-Triploid Mosaicism: An Unusual Phenomenon in Side-Necked Turtles (
Platemys platycephala
)
Authors: Bickham John W. , Tucker Priscilla K. , Legler John M.
Published: October 2006

Diploid and diploid-triploid mosaic individuals of
Platemys platycephala
were found in natural populations. In mosaic specimens, the blood, spleen, liver, and testis contained both diploid and triploid cells. The ratio of triploid to diploid cells was more variable among individuals than among somatic tissues within an individual. Only diploid cells underwent meiosis in males; haploid gametes were produced. There appears to be geographic variation for mosaicism in that only diploids were found in Bolivia, whereas diploids and diploid-triploid mosaics occurred in Surinam.
Characterization of "Peak E," a Novel Amino Acid Associated with Eosinophilia-Myalgia Syndrome
Authors: Mayeno Arthur N. , Lin Feng , Foote Christopher S. , Loegering David A. , Ames Matthew M. , Hedberg Craig W. , Gleich Gerald J.
Published: October 2006

Epidemiologic studies strongly associate eosinophilia-myalgia syndrome (EMS) with ingestion of tryptophan containing a contaminant ("peak E"). Prior reports have suggested that peak E is the di-tryptophan Nα-animal of acetaldehyde. Spectral and chemical studies now demonstrate that peak E is 1,1′-ethylidenebis[tryptophan]. This novel amino acid may be the etiological agent responsible for EMS, or it may be a marker of a still unidentified causal agent.
Herbicide Resistance and Cross-Resistance: Changes at Three Distinct Sites in the Herbicide-Binding Protein
Authors: Erickson Jeanne M. , Rahire Michèle , Rochaix Jean-David , Mets Laurens
Published: October 2006

Plants and algae resistant to the commonly used
s
-triazine herbicides display a wide spectrum of cross-resistance to other herbicides that act in a similar manner. Analysis of uniparental mutants of the green alga
Chlamydomonas reinhardi
showed that three different amino acid residues in the 32-kilodalton thylakoid membrane protein can be independently altered to produce three different patterns of resistance to
s
-triazine and urea-type herbicides. These results clarify the molecular basis for herbicide resistance and cross-resistance. Two of the mutations do not alter normal electron transport and thus may have applications of agronomic interest.
Study by Synchrotron Radiation of the Structure of a Working Catalyst at High Temperatures and Pressures
Authors: Boudart M. , Dalla Betta R.A. , Foger K. , Löffler D. G. , Samant M. G.
Published: October 2006

A relation among activity, composition, and structure was determined for a working catalyst by means of a stainless-steel reactor cell of novel design that permitted operation at temperatures and pressures similar to those in industrial reactors. Molybdenum K-edge x-ray absorption spectra were used to probe the structural environment of molybdenum in CoMoS/γ-alumina catalysts while hydrodesulfurization of benzothiophene was proceeding at high temperature and pressure. For catalyst samples with different contents of cobalt, radial structure functions obtained from extended x-ray absorption fine structure data presented the same features as those obtained from the spectra of MoS
2
/γ-alumina reference samples. Moreover, Mo-S and Mo-Mo coordination numbers were maximum for the sample with an atomic ratio of Co to (Co + Mo) of 0.33; this sample was also the most active catalyst tested.
Occurrence of Giant Impacts During the Growth of the Terrestrial Planets
Authors: Wetherill George W.
Published: October 2006

Three-dimensional Monte Carlo simulations of the accumulation of the terrestrial planets in the absence of gas drag produced results that are in general agreement with the number and distribution of the present planets. The accumulation process appears to be characterized by impact of bodies as large as three times the mass of Mars at velocities of about 9 kilometers per second. These giant impacts on Earth may have supplied the material and angular momentum that formed the moon, should have heated Earth to the melting point, and may have been responsible for the differences in the content of inert gases of the atmospheres of Earth and Venus.
Chronic Herbivory: Impacts on Architecture and Sex Expression of Pinyon Pine
Authors: Whitham Thomas G. , Mopper Susan
Published: October 2006

Pinyon pine,
Pinus edulis
(Engelm.), in Northern Arizona is exposed to recurring high levels of herbivory by the moth
Dioryctria albovitella
(Hust.). During a 3-year period, infested trees experienced on average a 30 percent reduction in annual shoot production. This herbivory affects tree architecture, growth rate, reproductive output, and sexual expression. Less infested trees produce 47 percent more trunk wood, 43 percent more branch wood, and are monoecious. Architectural changes in infested trees can result infunctionally male plants due to a complete loss of normal female cone-bearing ability. When herbivores are experimentally removed, normal growth and reproduction patterns resume. These strong herbivore impacts should represent a potent selection pressure in the evolution of host traits.
The Fajada Butte Solar Marker: A Reevaluation
Authors: Zeilik Michael
Published: October 2006

Evaluation of the Fajada Butte solar marker in Chaco Canyon, New Mexico, on the basis of its ethnographic context and usefulness for confirmatory and anticipatory solar observations indicates that the site does not function as an accurate solar calendar (accurate in the context of the historic Puebloan culture). The site most likely served as a sun shrine rather than as a calendrical observing station. The interpretation of the site as marking the northern declinations of the lunar 18.6-year cycle is not supported by the ethnographic evidence nor can the site be used to anticipate accurately the year of the standstill.
Radiative Properties of the Background Aerosol: Absorption Component of Extinction
Authors: Clarke Antony D. , Charlson Robert J.
Published: October 2006

The light-scattering and light-absorption coefficients of the global background aerosol define its single-scatter albedo. Continuous, simultaneous measurements of these optical coefficients were made on a daily basis for the remote marine mid-troposphere; such measurements are essential for assessment of the effects of aerosol on atmospheric radiative transfer. Measurements of light-absorption coefficients made at the Mauna Loa Observatory in Hawaii were higher than expected, and the single-scatter albedo was lower than the value often used in radiative transfer models. Soot appears to be the most likely primary absorber, and hemispheric dispersal of this combustion-derived material is suggested.
Identification of Geranylgeranyl-Modified Proteins in HeLa Cells
Authors: Farnsworth Christopher C. , Gelb Michael H. , Glomset John A.
Published: October 2006

Previous studies have shown that animal cells contain isoprenoid-modified proteins and that one of these proteins, lamin B, contains a thioether-linked farnesyl group that is attached to cysteine. In the present study, a novel isoprenoid-modification was identified by labeling HeLa cells with [
3
H]mevalonic acid and analyzing proteolytic digests of the total cell protein. Radioactive fragments were purified from these digests and treated with Raney nickel. The released, labeled material was analyzed by gas-liquid chromatography (GC) and mass spectrometry (MS). This approach revealed that an all
trans
geranylgeranyl group was a major isoprenoid modification.
A Cyanobacterium Capable of Swimming Motility
Authors: Waterbury John B. , Willey Joanne M. , Franks Diana G. , Valois Frederica W. , Watson Stanley W.
Published: October 2006

A novel cyanobacterium capable of swimming motility was isolated in pure culture from several locations in the Atlantic Ocean. It is a small unicellular form, assignable to the genus
Synechococcus
, that is capable of swimming through liquids at speeds of 25 micrometers per second. Light microscopy revealed that the motile cells display many features characteristic of bacterial flagellar motility. However, electron microscopy failed to reveal flagella and shearing did not arrest motility, indicating that the cyanobacterium may be propelled by a novel mechanism.
A Decline in Lead Transport by the Mississippi River
Authors: Trefry John H. , Metz Simone , Trocine Robert P. , Nelsen Terry A.
Published: October 2006

Inputs of pollutant lead to the Gulf of Mexico from the Mississippi River have declined by about 40 percent within the past decade. This decrease has been determined from annual lead loads of the Mississippi River and from the lead record in Mississippi Delta sediments. The observed trend is consistent with reduced consumption of lead in gasoline in the United States. More than 90 percent of the riverborne lead is associated with suspended sediments. Most of this particle-bound lead is deposited within 50 kilometers of the river mouth and is not easily leached at
p
H values above 3.
Ligand-Induced Transformation by a Noninternalizing Epidermal Growth Factor Receptor
Authors: Wells Alan , Welsh John B. , Lazar Cheri S. , Wiley H. Steven , Gill Gordon N. , Rosenfeld Michael G.
Published: October 2006

Identification of a mutant epidermal growth factor (EGF) receptor that does not undergo downregulation has provided a genetic probe to investigate the role of internalization in ligand-induced mitogenesis. Contact-inhibited cells expressing this internalization-defective receptor exhibited a normal mitogenic response at significantly lower ligand concentrations than did cells expressing wild-type receptors. A transformed phenotype and anchorage-independent growth were observed at ligand concentrations that failed to elicit these responses in cells expressing wild-type receptors. These findings imply that activation of the protein tyrosine kinase activity at the cell membrane is sufficient for the growth-enhancing effects of EGF. Thus, downregulation can serve as an attenuation mechanism, without which transformation ensues.
Colliding and Merging Galaxies
Authors: Schweizer François
Published: October 2006

Aided by advances in computer technology and observations from space, astronomers have begun to unravel the mysteries of galaxy formation and evolution. Galaxies evolve by interacting with their environment and especially with each other. During brief but often fierce galactic encounters, gravitational forces generate strong tides that survive as telltale signatures for billions of years. Because these so-called collisions dissipate orbital energy, galaxies on bound orbits may eventually merge. Collisions and mergers are responsible for a great variety of phenomena, including the triggering of widespread star formation in galaxies and the fueling of nuclear activity in quasars. Evidence is accumulating that not all galaxies formed shortly after the Big Bang. A sizable fraction of them may have formed later, and many are still experiencing significant dynamical evolution.
Organic Carbon-14 in the Amazon River System
Authors: Hedges John I. , Ertel John R. , Quay Paul D. , Grootes Pieter M. , Richey Jeffrey E. , Devol Allan H. , Farwell George W. , Schmidt Fred W. , Salati Eneas
Published: October 2006

Coarse and fine suspended particulate organic materials and dissolved humic and fulvic acids transported by the Amazon River all contain bomb-produced carbon-14, indicating relatively rapid turnover of the parent carbon pools. However, the carbon-14 contents of these coexisting carbon forms are measurably different and may reflect varying degrees of retention by soils in the drainage basin.
Atomic-Resolution Microscopy in Water
Authors: Sonnenfeld Richard , Hansma Paul K.
Published: October 2006

The scanning tunneling microscope is revolutionizing the study of surfaces. In ultrahigh vacuum it is capable not only of imaging individual atoms but also of determining energy states on an atom-by-atom basis. It is now possible to operate this instrument in water. Aqueous optical microscopy is confined to a lateral resolution limit of about 2000 angstroms, and aqueous x-ray microscopy has yielded a lateral resolution of 75 angstroms. With a scanning tunneling microscope, an image of a graphite surface immersed in deionized water was obtained with features less than 3 angstroms apart clearly resolved. Further, an image measured in saline solution demonstrated that the instrument can be operated under conditions useful for many biological samples.
Neurotrophin-3: a Neurotrophic Factor Related to NGF and BDNF
Authors: Maisonpierre Peter C. , Belluscio Leonardo , Squinto Stephen , Ip Nancy Y. , Furth Mark E. , Lindsay Ronald M. , Yancopoulos George D.
Published: October 2006

The development and maintenance of the nervous system depends on proteins known as neurotrophic factors. Although the prototypical neurotrophic factor, nerve growth factor (NGF), has been intensively studied for decades, the discovery and characterization of additional such factors has been impeded by their low abundance. Sequence homologies between NGF and the recently cloned brain-derived neurotrophic factor (BDNF) were used to design a strategy that has now resulted in the cloning of a gene encoding a novel neurotrophic factor, termed neurotrophin-3 (NT-3). The distribution of NT-3 messenger RNA and its biological activity on a variety of neuronal populations clearly distinguish NT-3 from NGF and BDNF, and provide compelling evidence that NT-3 is an authentic neurotrophic factor that has its own characteristic role in vivo.
A Cusp Singularity in Surfaces That Minimize an Anisotropic Surface Energy
Authors: Taylor Jean E. , Cahn John W.
Published: October 2006

A mathematical proof shows that a surface with a cusp-shaped singularity can arise from minimizing an anisotropic surface free energy for a portion of a crystal surface. Such cusps have been seen on crystal surfaces but usually have been interpreted as being the result of defects or nonequilibrium crystal growth. Our result predicts that they can occur as equilibrium or near-equilibrium phenomena. It also enriches the mathematical theory of minimal surfaces.
Cliff Swallow Colonies as Information Centers
Authors: Brown Charles R.
Published: October 2006

Colonies of cliff swallows (Aves:
Hirundo pyrrhonota
) appear to be information centers in which colony residents acquire information on the location of food sources. Individuals that have been unsuccessful on a foraging trip return to the colony, locate a successful forager, and follow that individual to a food source. Individuals often follow, and are followed by, their neighbors within the colony, possibly because neighbors can observe foraging success through food brought back to nestlings. All individuals are equally likely to follow others or be followed, and thus all individuals benefit from opportunities to receive information.
Sensory Tuning of Lateral Line Receptors in Antarctic Fish to the Movements of Planktonic Prey
Authors: Montgomery John C. , MacDonald John A.
Published: October 2006

The suitability of the lateral line system of fish and aquatic amphibia for the detection of planktonic prey was examined in the antarctic fish
Pagothenia borchgrevinki
(family Nototheniidae). The best responses of primary afferent lateral line neurons to waterborne vibrations were recorded at frequencies within the range of those produced by swimming crustacea. Simultaneous recordings from a swimming zooplankter held close to the fish and from primary afferent neurons provided direct confirmation that swimming movements of crustaceans are a potent natural stimulus of the lateral line system.
Time-Resolved Three-Dimensional Concentration Measurements in a Gas Jet
Authors: Yip Brandon , Lam Joseph K. , Winter Michael , Long Marshall B.
Published: October 2006

Turbulence can greatly influence reaction and heat transfer rates in fluids. The topology of the three-dimensional interface between mixing fluids directly determines the location and degree of reaction. The time-resolved measurement of the three-dimensional concentration field in a transitional gas jet is reported. A thin sheet of laser light was swept through the flow volume by a rotating mirror in a time brief enough that motion of the gas was minimal. The light sheet illuminated different parallel planes within the flow, and light scattered from particles seeding the jet was imaged onto a detector. The series of two-dimensional measurements made during one scan of the flow volume constituted a full three-dimensional mapping of structures within the flow. Computer graphics software was used to reconstruct and visualize three-dimensional surfaces of constant concentration and the magnitude of the concentration gradient vector over such surfaces.
Gene Transfer in Crop Improvement
Authors: Goodman Robert M. , Hauptli Holly , Crossway Anne , Knauf Vic C.
Published: October 2006

Transfer of genes between plant species has played an important role in crop improvement for many decades. Useful traits such as resistance to disease, insects, and stress have been transferred to crop varieties from noncultivated plants. Recombinant DNA methods greatly extend (even outside the plant kingdom) the sources from which genetic information can be obtained for crop improvement. Gene transfer systems based on recombinant DNA are available for several crop species and are under development for others. The concerted use of traditional and more recent methods for plant genetic manipulation will contribute to crop improvement.
Chemical Mimicry: Bolas Spiders Emit Components of Moth Prey Species Sex Pheromones
Authors: Stowe Mark K. , Tumlinson James H. , Heath Robert R.
Published: October 2006

Field studies have indicated that bolas spiders attract male moth prey, apparently by mimicking the odor of female moth sex pheromones. Three moth sex pheromone compounds, (
Z
)-9-tetradecenyl acetate, (
Z
)-9-tetradecenal, and (
Z
)-11-hexadecenal, were identified in volatile substances emitted by hunting adult female
Mastophora cornigera
spiders. These compounds are components of pheromone blends that attract some of this spider's moth prey species.
Duplication of CaMV 35
S
Promoter Sequences Creates a Strong Enhancer for Plant Genes
Authors: Kay Robert , Chan Amy , Daly Mark , McPherson Joan
Published: October 2006

A variant of the cauliflower mosaic virus 35
S
promoter with transcriptional activity approximately tenfold higher than that of the natural promoter was constructed by tandem duplication of 250 base pairs of upstream sequences. The duplicated region also acted as a strong enhancer of heterologous promoters, increasing the activity of an adjacent and divergently transcribed transferred DNA gene several hundredfold, and to a lesser extent, that of another transferred DNA gene from a remote downstream position. This optimized enhancer element should be very useful for obtaining high levels of expression of foreign genes in transgenic plants.
The Role of Ocular Muscle Proprioception in Visual Localization of Targets
Authors: Gauthier Gabriel M. , Nommay Danielle , Vercher Jean-Louis
Published: October 2006

The role of ocular muscle proprioception in the localization of visual targets has been investigated in normal humans by deviating one eye to create an experimental strabismus. The passively deviated eye was covered and the other eye viewed the target. With a hand-pointing task, targets were systematically mislocalized in the direction of the deviated nonviewing eye. A 4- to 6-degree error resulted when the nonviewing eye was offset 30 degrees from straight ahead. When the eye was deviated, the perceived "straight-ahead" was also displaced, by a similar amount, in the same direction. Since the efferent motor commands to the displaced and to the nondisplaced eyes are presumably identical by the law of equal innervation, the mislocalization of visual objects must be attributed to the change in proprioceptive information issued from the nonviewing, deviated eye. Thus proprioception contributes to the localization of objects in space.
Improved Orbital and Physical Parameters for the Pluto-Charon System
Authors: Tholen David J. , Buie Marc W. , Binzel Richard P. , Frueh Marian L.
Published: October 2006

Analysis of the observations of several Pluto-Charon occultation and transit events in 1985 and 1986 has provided a more detailed knowledge of the system. The sum of the radii of Pluto and Charon is 1786 ± 19 kilometers, but the individual radii are somewhat more poorly determined; Pluto is 1145 ± 46 kilometers in radius and Charon is 642 ± 34 kilometers in radius. The mean density of the system is 1.84 ± 0.19 grams per cubic centimeter, implying that more than half of the mass is due to rock. Charon appears to have hemispheres of two different colors, the Pluto-facing side being neutral in color and the opposite hemisphere being a reddish color similar to Pluto.
An Invariance in the Isoheptanes of Petroleum
Authors: Mango Frank D.
Published: October 2006

Four isoheptanes in petroleum display a remarkable invariance in a ratio of sums of concentrations. The isoheptanes are not at thermodynamic equilibrium, nor are they fixed to some constant composition. The four isomers display coherent change in relative amounts but maintain invariance in the ratio of sums. Within sets of genetically related petroleum samples, invariance reaches levels that approach the limits of our analytical precision. The invariance is inconsistent with a chemical origin that involves the thermal fragmentation of natural products or their derivatives. It suggests a reaction process at steady state, in which relative rates of product formation are constant. A mechanism is proposed in which the four isoheptanes are formed pairwise and sequentially through two intermediates in a catalytic process that operates at steady state.
The Social Process of International Migration
Authors: Massey Douglas S. , España Felipe García
Published: October 2006

The social process of network growth helps to explain the rapid increase in the migration of Mexicans to the United States during the 1970s. Migrant networks are webs of social ties that link potential migrants in sending communities to people in receiving societies, and their existence lowers the costs of international movement. With each person that becomes a migrant, the cost of migration is reduced for a set of friends and relatives, inducing them to migrate and further expanding the network. As a result of this dynamic interaction, network connections to the United States have become widespread throughout Mexico, and the probability of international migration from that country is high.