bluuebunny/crossref_metadata_2025 huggingface dataset:
The Titan -1:0 Nodal Bending Wave in Saturn's Ring C
Authors: Rosen Paul A. , Lissauer Jack J.
Published: October 2006

The most prominent oscillatory feature observed in the Voyager 1 radio occultation of Saturn's rings is identified as a one-armed spiral bending wave excited by Titan's -1:0 nodal inner vertical resonance. Ring particles in a bending wave move in coherently inclined orbits, warping the local mean plane of the rings. The Titan -1:0 wave is the only known bending wave that propagates outward, away from Saturn, and the only spiral wave yet observed in which the wave pattern rotates opposite to the orbital direction of the ring particles. It is also the first bending wave identified in ring C. Modeling the observed feature with existing bending wave theory gives a surface mass density of ∼0.4 g/cm
2
outside the wave region and a local ring thickness of ≲5 meters, and suggests that surface mass density is not constant in the wave region.
Processing Techniques for the 93 K Superconductor Ba
2
YCu
3
O
7
Authors: Murphy D. W. , Johnson D. W. , Jin S. , Howard R. E.
Published: October 2006

Superconductivity above the temperature of liquid nitrogen in copper oxide-based systems has led to optimism that superconductors may at last find wide application. The critical temperature, however, is just one of the required parameters. The materials must be made into usable forms such as wire, thick films, thin films, and bulk ceramics. In addition, the critical current in these various forms is a crucial test of their utility. This article reviews the processing techniques used to fabricate potentially useful forms and assesses remaining problems. Considerable improvement in critical current density is necessary in bulk materials, and thin films need to be made compatible with other thin-film technology.
Neutron Imaging of Laser Fusion Targets
Authors: Ress D. , Lerche R. A. , Ellis R. J. , Lane S. M. , Nugent K. A.
Published: October 2006

A long-term goal of inertial-confinement fusion research is the generation of energy by imploding capsules containing deuterium-tritium fuel. Progress in designing the capsules is aided by accurate imaging of the fusion burn. Penumbral coded-aperture techniques have been used to obtain neutron images that are a direct measurement of the fusion burn region in the capsules.
A Novel Target for Antidiuretic Hormone in Insects
Authors: Spring Jeffrey H. , Morgan Anne M. , Hazelton Shelia R.
Published: October 2006

Diuresis in insects is controlled by two antagonistic hormone groups: diuretic hormones, which promote water loss, and antidiuretic hormones, which inhibit it. All known antidiuretic factors act solely to promote fluid reabsorption by the hindgut and do not affect secretion by the Malpighian tubules. In the house cricket,
Acheta domesticus
, an antidiuretic hormone was found that inhibits fluid secretion by the Malpighian tubules but has no effect on the hindgut. Correlations were found between the density of neurosecretory granules and the presence of antidiuretic hormone in the corpora cardiaca, suggesting that the hormone is released from specific axons. Its release is triggered by dehydration; the hormone is detectable in the hemolymph of water-deprived crickets. These results imply that an unusual mechanism regulates water balance in these insects.
Synthesis and Properties of Metallic Glasses That Contain Aluminum
Authors: He Y. , Poon S. J. , Shiflet G. J.
Published: October 2006

The synthesis and properties of a class of metallic glasses containing up to 90 atomic percent aluminum are reported. The unusual formability of the glasses and their structural features are pointed out. Mechanical properties including tensile fracture strength and Young's modulus are reported along with crystallization temperatures. The unusually high strengths of the aluminum glasses can be of significant importance in obtaining high-strength low-density materials.
Industrial Innovation in Japan and the United States
Authors: Mansfield Edwin
Published: October 2006

Japanese firms tend to be quicker and more economical than U.S. firms at developing and introducing new products and processes, but this advantage seems to exist only among innovations based on external technology, rather than internal technology. Whereas U.S. firms put more emphasis on marketing start-up, they put much less emphasis on tooling, equipment, and manufacturing facilities than do Japanese firms. Applied R&D in Japan, which focuses more on processes than in the United States, seems to have yielded a handsome return; but there is no evidence that the rate of return from basic research has been relatively high in Japan. In robotics, the Japanese edge seems to increase as one moves from R&D toward the market.
Predator-Prey Role Reversal in a Marine Benthic Ecosystem
Authors: Barkai Amos , McQuaid Christopher
Published: October 2006

Two closely located islands on the west coast of South Africa support widely different benthic communities. The biota at Malgas Island is dominated by seaweeds and by rock lobsters that consume settling mussels, thereby preventing the establishment of the mussels. They also prey on whelks, although one species,
Burnupena papyracea,
is protected from predation by a commensal bryozoan that covers its shell. Marcus Island has extensive mussel beds, but rock lobsters and seaweeds are virtually absent; whelks (mostly
Burnupena
spp.) occur at high densities. Rock lobsters transferred to Marcus Island were overwhelmed and consumed by the whelks, reversing the normal predator-prey relation between the two species. These two contrasting communities persisted during 4 years and may represent multiple states of the same ecosystem. This effective change of roles between a prey species and its chief predator may provide an intrinsic mechanism to maintain these states following the initial exclusion of the predator.
Nitrogen Fixation by Anaerobic Cellulolytic Bacteria
Authors: Leschine S. B. , Holwell K. , Canale-Parola E.
Published: October 2006

Four strains of anaerobic nitrogen-fixing, cellulose-fermenting bacteria were isolated in pure culture from freshwater mud and soil. Nitrogenase activity was demonstrated in these strains and also in several previously described anaerobic cellulolytic bacteria isolated from various natural environments. These are the first anaerobic bacteria known to use cellulose as an energy source for nitrogen fixation. Because cellulose is a plant polysaccharide that abounds in nature, these results raise the possibility that nitrogen-fixing, cellulose-fermenting bacteria may be widespread and thus play a major role in carbon and nitrogen cycling.
Nucleotide Sequence of a Bovine Clone Encoding the Angiogenic Protein, Basic Fibroblast Growth Factor
Authors: Abraham Judith A. , Mergia Ayalew , Whang Jacqueline L. , Tumolo Annette , Friedman Jeff , Hjerrild Kathryn A. , Gospodarowicz Denis , Fiddes John C.
Published: October 2006

Basic and acidic fibroblast growth factors (FGF's) are potent mitogens for capillary endothelial cells in vitro, stimulate angiogenesis in vivo, and may participate in tissue repair. An oligonucleotide probe for bovine basic FGF was designed from the nucleotide sequence of the amino-terminal exon of bovine acidic FGF, taking into account the 55 percent amino acid sequence homology between the two factors. With this oligonucleotide probe, a full length complementary DNA for basic FGF was isolated from bovine pituitary. Basic FGF in bovine hypothalamus was shown to be encoded by a single 5.0-kilobase messenger RNA; in a human hepatoma cell line, both 4.6- and 2.2-kilobase basic FGF messenger RNA's were present. Both growth factors seem to be synthesized with short amino-terminal extensions that are not found on the isolated forms for which the amino acid sequences have been determined. Neither basic nor acidic FGF has a classic signal peptide.
Altered Regulation of Airway Epithelial Cell Chloride Channels in Cystic Fibrosis
Authors: Frizzell Raymond A. , Rechkemmer Gerhard , Shoemaker Richard L.
Published: October 2006

In many epithelial cells the chloride conductance of the apical membrane increases during the stimulation of electrolyte secretion. Single-channel recordings from human airway epithelial cells showed that β-adrenergic stimulation evoked apical membrane chloride channel activity, but this response was absent in cells from patients with cystic fibrosis (CF). However, when membrane patches were excised from CF cells into media containing sufficient free calcium (approximately 180 nanomolar), chloride channels were activated. The chloride channels of CF cells were similar to those of normal cells as judged by their current-voltage relations, ion selectivity, and kinetic behavior. These findings demonstrate the presence of chloride channels in the apical membranes of CF airway cells. Their regulation by calcium appears to be intact, but cyclic adenosine monophosphate (cAMP)-dependent control of their activity is defective.
Ion Channels in Yeast
Authors: Gustin Michael C. , Martinac Boris , Saimi Yoshiro , Culbertson Michael R. , Kung Ching
Published: October 2006

Voltage-dependent ion channels have been found in the plasma membrane of the yeast
Saccharomyces cerevisiae
. Ion channel activities were recorded from spheroplasts or patches of plasma membrane with the patch-clamp technique. The most prominent activities came from a set of potassium channels with the properties of activation by positive but not negative voltages, high selectivity for potassium over sodium ion, unit conductance of 20 picosiemens, inhibition by tetraethylammonium or barium ions, and bursting kinetics.
Nature and Nurture in Development of the Autonomic Neuron
Authors: Bunge Richard , Johnson Mary , Ross C. David
Published: October 2006

Arguments are presented for the hypothesis that during an early stage of development the cells which become principal neurons of the autonomic nervous system possess information regarding the positions they will occupy within the body. A second stage of development, during which a decision is made regarding which neurotransmitter to employ, is delayed until each neuron has assumed its permanent position in the body and has sampled, presumably via its growing axons, the peripheral field which it will innervate. The development of cholinergic mechanisms takes precedence; adrenergic neurons may develop only when cholinergic sites have been occupied. An extended period during which the differentiation of transmitter mechanisms may be modulated permits the neuron to adequately sample the periphery prior to commitment to a specific transmitter economy.
Cloud-Radiative Forcing and Climate: Results from the Earth Radiation Budget Experiment
Authors: Ramanathan V. , Cess R. D. , Harrison E. F. , Minnis P. , Barkstrom B. R. , Ahmad E. , Hartmann D.
Published: October 2006

The study of climate and climate change is hindered by a lack of information on the effect of clouds on the radiation balance of the earth, referred to as the cloud-radiative forcing. Quantitative estimates of the global distributions of cloud-radiative forcing have been obtained from the spaceborne Earth Radiation Budget Experiment (ERBE) launched in 1984. For the April 1985 period, the global shortwave cloud forcing [-44.5 watts per square meter (W/m
2
)] due to the enhancement of planetary albedo, exceeded in magnitude the longwave cloud forcing (31.3 W/m
2
) resulting from the greenhouse effect of clouds. Thus, clouds had a net cooling effect on the earth. This cooling effect is large over the mid- and high-latitude oceans, with values reaching -100 W/m
2
. The monthly averaged longwave cloud forcing reached maximum values of 50 to 100 W/m
2
over the convectively disturbed regions of the tropics. However, this heating effect is nearly canceled by a correspondingly large negative shortwave cloud forcing, which indicates the delicately balanced state of the tropics. The size of the observed net cloud forcing is about four times as large as the expected value of radiative forcing from a doubling of CO
2
. The shortwave and longwave components of cloud forcing are about ten times as large as those for a CO
2
doubling. Hence, small changes in the cloud-radiative forcing fields can play a significant role as a climate feedback mechanism. For example, during past glaciations a migration toward the equator of the field of strong, negative cloud-radiative forcing, in response to a similar migration of cooler waters, could have significantly amplified oceanic cooling and continental glaciation.
Involvement of Juvenile Hormone in the Regulation of Pheromone Release Activities in a Moth
Authors: Cusson Michel , McNeil Jeremy N.
Published: October 2006

Juvenile hormone has been implicated in the mediation of several reproduction-related events in adult insects, but had previously been found to play no role in the regulation of sex pheromone production and release behavior ("calling") in moths. In females of the true armyworm moth,
Pseudaletia unipuncta
, juvenile hormone is shown to be essential to the initiation of both calling behavior and pheromone production. Females without corpora allata, the source of juvenile hormone, do not call and do not produce pheromone, but injection of juvenile hormone into allatectomized females restored these activities. The armyworm's control system has likely evolved in response to the adults' migratory behavior which may necessitate that mating be restricted to the period following migration.
Atomic Resolution Imaging of Adsorbates on Metal Surfaces in Air: Iodine Adsorption on Pt(111)
Authors: Schardt Bruce C. , Yau Shueh-Lin , Rinaldi Frank
Published: October 2006

The adsorption of iodine on platinum single crystals was studied with the scanning tunneling microscope (STM) to define the limits of resolution that can be obtained while imaging in air and to set a target resolution for STM imaging of metal surfaces immersed in an electrochemical cell. Two iodine adlattice unit cells of slightly different iodine packing density were clearly imaged: (√7 × √7)
R
19.1°-I, surface coverage θ
I
= 3/7; and (3 × 3)-I, θ
I
= 4/9. The three iodine atoms in the (√7 × √7) unit cell form a regular hexagonal lattice interatomic distance
d
I
= 0.424 nanometer, with two atoms adsorbed in threefold hollow sites and one atom adsorbed at an atop site. The (3 × 3) unit cell showed two different packing arrangements of the four iodine atoms exit. In one of the (3 × 3) structures, the iodine atoms pack to form a hexagonal lattice,
d
I
= 0.417 nanometer, with three of the iodine atoms at twofold adsorption sites and one atom at an atop site. Another packing arrangement of iodine into the (3 × 3) unit cell was imaged in which the iodine atoms are not arranged symmetrically.
Oligodendrocyte Adhesion Activates Protein Kinase C-Mediated Phosphorylation of Myelin Basic Protein
Authors: Vartanian Timothy , Szuchet Sara , Dawson Glyn , Campagnoni Anthony T.
Published: October 2006

When isolated adult oligodendrocytes adhere to a substratum myelinogenesis occurs. Investigation of the mechanism by which this happens indicated that the oligodendrocyte-substratum interaction (i) activated protein kinase C-dependent phosphorylation of myelin basic protein and (ii) promoted the synthesis of myelin basic protein. In addition, when agents that activate protein kinase C (second messenger diacylglycerol or a tumor-promoting phorbol ester) were added to nonattached oligodendrocytes, they mimicked the influence of the substratum by inducing phosphorylation of myelin basic protein; and reagents that increase cellular adenosine 3′, 5′-monophosphate (cyclic AMP) inhibited phosphorylation of myelin basic protein. Thus, at least in vitro, the interaction between oligodendrocytes and the substratum may mediate myelinogenic events, and phosphorylation of myelin basic protein may be an early requirement in the sequence of steps that ultimately results in myelin formation.
Forskolin and Phorbol Esters Reduce the Same Potassium Conductance of Mouse Neurons in Culture
Authors: Grega Debra S. , Werz Mary Ann , MacDonald Robert L.
Published: October 2006

Second messenger systems may modulate neuronal activity through protein phosphorylation. However, interactions between two major second messenger pathways, the cyclic AMP and phosphatidylinositol systems, are not well understood. The effects of activators of cyclic AMP-dependent protein kinase and protein kinase C on resting membrane properties, action potentials, and currents recorded from mouse dorsal root ganglion neurons and cerebral hemisphere neurons grown in primary dissociated cell culture were investigated. Neither forskolin (FOR) nor phorbol 12,13-dibutyrate (PDBu) altered resting membrane properties but both increased the duration of calcium-dependent action potentials in both central and peripheral neurons. By means of the single-electrode voltage clamp technique, FOR and PDBu were shown to decrease the same voltage-dependent potassium conductance. This suggests that two independent second messenger systems may affect the same potassium conductance.
Characterization and Clinical Association of Antibody Inhibitory to HIV Reverse Transcriptase Activity
Authors: Laurence Jeffrey , Saunders Anne , Kulkosky Joseph
Published: October 2006

Reverse transcriptase activity of the human immunodeficiency virus (HIV) was blocked in vitro by immunoglobulin G (IgG) derived from certain individuals infected with this retrovirus. A heterogeneous immune response for inhibition of enzyme function was noted. Catalytic activity was depressed by 50% or more with the use of 10 micrograms of IgG from 11 of 16 HIV-seropositive asymptomatic carriers, but from 0 of 8 seronegative controls and 2 of 12 patients with acquired immune deficiency syndrome (AIDS) or the AIDS-related complex (ARC). The inhibitor was confined to the F(ab′)
2
fragment. It was not directed against the poly(rA) ⋅ oligo(dT) template, nor against major envelope or structural viral antigens, and did not cross-react with bacterial, avian, or other mammalian DNA polymerases. It did not correlate with recognition of polymerase antigens by radioimmunoprecipitation. Loss of this inhibitor may be associated with development of clinical disease. Ten asymptomatic HIV-seropositive carriers with high titers of IgG antibodies to reverse transcriptase were followed for a mean of 3 years. All of four lost inhibitory capability prior to development of AIDS or ARC, while titers persist in the six who remain clinically healthy.
The α Subunit of the GTP Binding Protein G
k
Opens Atrial Potassium Channels
Authors: Codina Juan , Yatani Atsuko , Grenet Dagoberto , Brown Arthur M. , Birnbaumer Lutz
Published: October 2006

Guanine nucleotide binding (G) proteins (subunit composition αβγ) dissociate on activation with guanosine triphosphate (GTP) analogs and magnesium to give α-guanine nucleotide complexes and free βγ subunits. Whether the opening of potassium channels by the recently described G
k
in isolated membrane patches from mammalian atrial myocytes was mediated by the α
k
subunit or βγ dimer was tested. The α
k
subunit was found to be active, while the βγ dimer was inactive in stimulating potassium channel activity. Thus, G
k
resembles G
s
, the stimulatory regulatory component of adenylyl cyclase, and transducin, the regulatory component of the visual system, in that it regulates its effector function—the activity of the ligand-gated potassium channel—through its guanine nucleotide binding subunit.
Seasonal Microhabitat Selection by an Endoparasitoid Through Adaptive Modification of Host Behavior
Authors: Brodeur Jacques , McNeil Jeremy N.
Published: October 2006

Differences in the distribution of parasitized and unparasitized hosts has been used to infer modification of host behavior by insect parasitoids. Data are presented showing that not only do parasitized hosts behave differently from unparasitized ones, but that the behavior of parasitized hosts varies in function of the physiological state of the parasitoid. Aphids containing nondiapausing parasitoids leave the aphid colony and mummify on the upper surface of the leaves, whereas those containing diapausing parasitoids leave the host plant and mummify in concealed sites. Modification of host behavior by diapausing parasitoids results in the selection of a suitable microhabitat that reduces the incidence of hyperparasitism and should decrease the action of adverse climatic conditions during the lengthy dormant period.
Air Pollution and Forest Decline in a Spruce (
Picea abies
) Forest
Authors: Schulze E.-D.
Published: October 2006

Symptoms of forest decline of spruce in Europe range from needle yellowing and loss to tree and stand mortality. In a study area in northeast Bavaria, West Germany, where forest decline was initially detected, exposure to high concentrations of gaseous pollutants, SO
2,
NO

x

, and ozone has had no long-lasting direct effect on needles, and pathogens have only been secondary agents. Deposition of sulfur, nitrate, and ammonium, however, have significantly modified plant nutrition and soil chemistry. Spruce roots apparently take up ammonium rather than nitrate with an antagonistic effect on uptake of Mg. Nitrate left in the soil solution is leached together with sulfate to ground water, accelerating soil acidification and decreasing Ca/Al and Mg/Al ratios in the soil solution. Soil solution chemistry affects root development, and water and nutrient uptake. Had all nutrients become equally deficient, spruce trees probably could have adjusted by retarding their growth. However, canopy uptake of atmospheric nitrogen in addition to root uptake stimulated growth and caused a nitrogen to cation imbalance to develop; this imbalance resulted in the decline symptoms.
Mammal-Like Dentition in a Mesozoic Crocodylian
Authors: Clark James M. , Jacobs Louis L. , Downs William R.
Published: October 2006

Crocodylian teeth are generally conical with little differentiation in shape along the tooth row. The mandible is incapable of any fore-aft movement, and feeding typically involves little or no intraoral processing. Complex, multi-cusped, mammal-like teeth differentiated along the tooth row have been found in a Cretaceous crocodylian from Malawi. The morphology of the teeth and mandible indicates that food items were processed by back-to-front (proal) movement of the mandible, unlike living crocodylians but as in some mammals and
Sphenodon
(the tuatara).
Model Substrates for an RNA Enzyme
Authors: McClain William H. , Guerrier-Takada Cecilia , Altman Sidney
Published: October 2006

M1 RNA, the catalytic RNA subunit of
Escherichia coli
ribonuclease P, can cleave novel transfer RNA (tRNA) precursors that lack specific domains of the normal tRNA sequence. The smallest tRNA precursor that was cleaved efficiently retained only the domain of the amino acid acceptor stem and the T stem and loop. The importance of the 3′ terminal CCA nucleotide residues in the processing of both novel and normal tRNA precursors implies that the same enzymatic function of M1 RNA is involved.
Effect of Membrane Potential Changes on the Calcium Transient in Single Rat Cardiac Muscle Cells
Authors: Cannell Mark B. , Berlin Joshua R. , Lederer William J.
Published: October 2006

The mechanism that links membrane potential changes to the release of calcium from internal stores to cause contraction of cardiac cells is unclear. By using the calcium indicator fura-2 under voltage-clamp conditions, changes in intracellular calcium could be monitored in single rat ventricular cells while controlling membrane potential. The voltage dependence of the depolarization-induced increase in intracellular calcium was not the same as that of the calcium current (
I
si
), which suggests that only a small fraction of
I
si
is required to trigger calcium release from the sarcoplasmic reticulum. In addition, sarcoplasmic reticulum calcium release may be partly regulated by membrane potential, since repolarization could terminate the rise in intracellular calcium. Thus, changes in the action potential will have immediate effects on the time course of the calcium transient beyond those associated with its effects on
I
si
.
Magnification of Secondary Production by Kelp Detritus in Coastal Marine Ecosystems
Authors: Duggins D. O. , Simenstad C. A. , Estes J. A.
Published: October 2006

Kelps are highly productive seaweeds found along most temperate latitude coastlines, but the fate and importance of kelp production to nearshore ecosystems are largely unknown. The trophic role of kelp-derived carbon in a wide range of marine organisms was assessed by a natural experiment. Growth rates of benthic suspension feeders were greatly increased in the presence of organic detritus (particulate and dissolved) originating from large benthic seaweeds (kelps). Stable carbon isotope analysis confirmed that kelp-derived carbon is found throughout the nearshore food web.
The Applications of Closure Phase to Astronomical Imaging
Authors: Cornwell T. J.
Published: October 2006

Closure phase is a number measured by triplets of Michelson interferometers that is completely independent of certain types of otherwise severe instrumental errors. In the 30 years since closure phase was invented, it has been applied to a diverse number of different problems in astronomical imaging. Methods based on the closure phase now allow imaging of complex objects in the presence of severe aberrations and are vital to the success of modern, high-resolution astronomical imaging both at radio and at optical wavelengths. Over the past 10 to 15 years, the concept of closure phase has been extended and generalized. One of the most important advances has been the development of automatic or self-calibration techniques. This article reviews closure phase methods and some of the many spin-offs and related ideas.
The Photosynthetic Reaction Center from the Purple Bacterium
Rhodopseudomonas viridis
Authors: Deisenhofer Johann , Michel Hartmut
Published: October 2006

The history and methods of membrane protein crystallization are described. The solution of the structure of the photosynthetic reaction center from the bacterium
Rhodopseudomonas viridis
is described, and the structure of this membrane protein complex is correlated with its function as a light-driven electron pump across the photosynthetic membrane. Conclusions about the structure of the photosystem II reaction center from plants are drawn, and aspects of membrane protein structure are discussed.
The α Subunit of the GTP Binding Protein Activates Muscarinic Potassium Channels of the Atrium
Authors: Cerbai E. , Klöckner U. , Isenberg G.
Published: October 2006

It has been debated whether the potassium channel of the atrium is activated by the α subunit or by the βγ subunits of guanine nucleotide binding (G) proteins, which dissociate on activation with guanosine triphosphate (GTP). Therefore, the channel-activating effectiveness of these subunits on isolated guinea pig atrial cells was tested. The activated α
K
subunit from human erythrocytes activated the channel in subpicomolar concentrations. The βγ dimer from bovine brain activated the channel in nanomolar concentrations. These results support the view that, physiologically, the α subunit activates the channel.
Three-Dimensional Structure at 0.86 Å of the Uncomplexed form of the Transmembrane Ion Channel Peptide Gramicidin A
Authors: Langs David A.
Published: October 2006

The crystal structure of the uncomplexed orthorhombic form of gramicidin A has been determined at 120 K and at 0.86 angstrom resolution. The pentadecapeptide crystallizes as a left-handed antiparallel double-stranded helical dimer with 5.6 amino acid residues per turn. The helix has an overall length of 31 angstroms and an average inner channel diameter of 4.80 angstroms. The channel of this crystalline form is void of ions or solvent molecules. The channel diameter varies from a minimum of 3.85 angstroms to a maximum of 5.47 angstroms and contains three pockets where the cross-channel contacts are 5.25 angstroms or greater. The range of variation seen for the φ and ψ torsion angles of the backbone of the helix suggests that these potential ion binding sites can be induced to travel the length of the channel in a peristaltic manner by cooperatively varying these angles. The indole rings of the eight tryptophan residues of the dimer are overlapped in three separate regions on the outer surface of the helix when viewed down the barrel of the channel. This arrangement would permit long-chained lipid molecules to nest parallel to the outer channel surface between these protruding tryptophan regions and act like molecular splines to constrain helical twist deformations of the channel.
The Coupling of Neurotransmitter Receptors to Ion Channels in the Brain
Authors: Nicoll Roger A.
Published: October 2006

Recent studies on the action of neurotransmitters on hippocampal pyramidal cells indicate that different neurotransmitter receptors that use either the same or different coupling mechanisms converge onto the same ion channel. Conversely, virtually all of the neurotransmitters act on at least two distinct receptor subtypes coupled to different ion channels on the same cell. The existence of both convergence and divergence in the action of neurotransmitters results in a remarkable diversity in neuronal signaling.
Amyloid Protein Precursor Messenger RNAs: Differential Expression in Alzheimer's Disease
Authors: Palmert M. R. , Golde T. E. , Cohen M. L. , Kovacs D. M. , Tanzi R. E. , Gusella J. F. , Usiak M. F. , Younkin L. H. , Younkin S. G.
Published: October 2006

In situ hybridization was used to assess total amyloid protein precursor (APP) messenger RNA and the subset of APP mRNA containing the Kunitz protease inhibitor (KPI) insert in 11 Alzheimer's disease (AD) and 7 control brains. In AD, a significant twofold increase was observed in total APP mRNA in nucleus basalis and locus ceruleus neurons but not in hippocampal subicular neurons, neurons of the basis pontis, or occipital cortical neurons. The increase in total APP mRNA in locus ceruleus and nucleus basalis neurons was due exclusively to an increase in APP mRNA lacking the KPI domain. These findings suggest that increased production of APP lacking the KPI domain in nucleus basalis and locus ceruleus neurons may play an important role in the deposition of cerebral amyloid that occurs in AD.
Movement Protein of Tobacco Mosaic Virus Modifies Plasmodesmatal Size Exclusion Limit
Authors: Wolf Shmuel , Lucas William J. , Deom Carl M. , Beachy Roger N.
Published: October 2006

The function of the 30-kilodalton movement protein (MP) of tobacco mosaic virus is to facilitate cell-to-cell movement of viral progeny in an infected plant. A novel method for delivering non-plasmalemma-permeable fluorescent probes to the cytosol of spongy mesophyll cells of tobacco leaves was used to study plasmodesmatal size exclusion limits in transgenic plants that express the MP gene. Movement of fluorescein isothiocyanate-labeled dextran (F-dextran) with an average molecular mass of 9400 daltons and an approximate Stokes radius of 2.4 nanometers was detected between cells of the transgenic plants, whereas the size exclusion limit for the control plants was 700 to 800 daltons. No evidence of F-dextran metabolism in the leaves of the transgenic plants was found. Thus, the tobacco mosaic virus movement protein has a direct effect on a plasmodesmatal function.
The Unending Deposit Insurance Mess
Authors: Kane Edward J.
Published: October 2006

The thrift institution deposit insurance mess is rooted in defects in political and bureaucratic accountability. Under existing incentives, covering up evidence of poor regulatory performance and relaxing binding capital requirements are rational governmental responses to widespread industry insolvency. Similarly, aggressive industry risk taking is a rational response by thrift managers to regulatory forbearances. Far from acknowledging these incentive defects, the Bush plan for cleaning up the mess adopts theories that spotlight other causes: specifically, poor thrift management and the deregulation of thrift institution activities and of deposit interest rates. To end the mess, politicians and regulators must jettison these comfortable theories and surrender discretion that permits them to finesse the need to budget for governmental financial commitments.
Thermomolecular Pressure in Surface Melting: Motivation for Frost Heave
Authors: Dash J. G.
Published: October 2006

A thermomolecular pressure is associated with surface melting, and it can drive mass flow along an interface under a lateral temperature gradient. The pressure is a universal thermodynamic function in the limit of thick films. It may be responsible for frost heave in frozen ground.
A c-
myb
Antisense Oligodeoxynucleotide Inhibits Normal Human Hematopoiesis in Vitro
Authors: Gewirtz Alan M. , Calabretta Bruno
Published: October 2006

The nuclear protein encoded by the proto-oncogene c-
myb
has been hypothesized to play an important role in the process of hematopoiesis, but direct proof of this function has been lacking. To address this issue, normal human bone marrow mononuclear cells were exposed to c-
myb
sense and antisense synthetic oligodeoxynucleotides, and the effects on hematopoietic colony formation and maturation were examined. Exposure of these cells to c-
myb
antisense, oligodeoxynucleotides resulted in a decrease in both colony size and number, without apparent effect on the maturation of residual colony cells. Exposure to c-
myb
sense, or irrelevant antisense, oligonucleotides had no such effect. These results show that (i) c-
myb
plays a critical role in regulating normal human hematopoiesis and (ii) the combined use of antisense oligodeoxynucleotides and hematopoietic cell culture techniques will provide a powerful tool for studying the role of proteins encoded by proto-oncogenes, or other specific genes, in normal human hematopoiesis.
Evidence That the M2 Membrane-Spanning Region Lines the Ion Channel Pore of the Nicotinic Receptor
Authors: Leonard Reid J. , Labarca Cesar G. , Charnet Pierre , Davidson Norman , Lester Henry A.
Published: October 2006

Site-directed mutagenesis and expression in Xenopus oocytes were used to study acetylcholine receptors in which serine residues (i) were replaced by alanines (α, δ subunits) or (ii) replaced a phenylalanine (β subunit) at a postulated polar site within the M2 transmembrane helix. As the number of serines decreased, there were decreases in the residence time and consequently the equilibrium binding affinity of QX-222, a quaternary ammonium anesthetic derivative thought to bind within the open channel. Receptors with three serine-to-alanine mutations also displayed a selective decrease in outward single-channel currents. Both the direction of this rectification and the voltage dependence of QX-222 blockade suggest that the residues mutated are within the aqueous pore of the receptor and near its cytoplasmic (inner) surface.
Antisense RNA-Induced Reduction in Murine TIMP Levels Confers Oncogenicity on Swiss 3T3 Cells
Authors: Khokha Rama , Waterhouse Paul , Yagel Simcha , Lala Peeyush K. , Overall Christopher M. , Norton Gill , Denhardt David T.
Published: October 2006

Mouse 3T3 cell lines capable of constitutively synthesizing an RNA complementary to the messenger RNA encoding TIMP, tissue inhibitor of metalloproteinases, were constructed by transfection with appropriate plasmid constructs. Many of the lines were down-modulated for TIMP messenger RNA levels and secreted less TIMP into the culture medium. In comparison to noninvasive, nontumorigenic controls, these cells not only were invasive in a human amnion invasion assay, but also were tumorigenic and metastatic in athymic mice. These results indicate that TIMP suppresses oncogenicity, at least in immortal murine 3T3 cells.
Control of Angiogenesis with Synthetic Heparin Substitutes
Authors: Folkman Judah , Weisz Paul B. , Joullié Madeleine M. , Li William W. , Ewing William R.
Published: October 2006

Many diseases are dominated by persistent growth of capillary blood vessels. Tumor growth is also angiogenesis-dependent. Safe and effective angiogenesis inhibitors are needed to determine whether control of angiogenesis would be therapeutic. Heparin and certain steroids, administered together, can inhibit angiogenesis in a synergistic manner. This "pair" effect suggested that specific hydrophilic cycloamyloses may be suitable heparin substitutes. β-Cyclodextrin tetradecasulfate administered with a steroid inhibits angiogenesis at 100 to 1000 times the effectiveness of heparin in the chick embryo bioassay. This cyclic oligosaccharide also augments the anti-angiogenic effect of angiostatic steroids against corneal neovascularization in rabbits when β-cyclodextrin tetradecasulfate and a steroid are inserted into the cornea or applied topically as eyedrops.
On Finding All Suboptimal Foldings of an RNA Molecule
Authors: Zuker Michael
Published: October 2006

An algorithm and a computer program have been prepared for determining RNA secondary structures within any prescribed increment of the computed global minimum free energy. The mathematical problem of determining how well defined a minimum energy folding is can now be solved. All predicted base pairs that can participate in suboptimal structures may be displayed and analyzed graphically. Representative suboptimal foldings are generated by selecting these base pairs one at a time and computing the best foldings that contain them. A distance criterion that ensures that no two structures are "too close" is used to avoid multiple generation of similar structures. Thermodynamic parameters, including free-energy increments for single-base stacking at the ends of helices and for terminal mismatched pairs in interior and hairpin loops, are incorporated into the underlying folding model of the above algorithm.
Stellar Activity and Brightness Variations: A Glimpse at the Sun's History
Authors: Radick Richard R. , Lockwood G. W. , Baliunas Sallie L.
Published: October 2006

Radiometric measurements during the past decade from the Solar Maximum Mission and Nimbus 7 satellites have shown that the total solar irradiance varies in step with the sun's 11-year magnetic activity cycle. Stellar observations from the Lowell and Mount Wilson observatories now confirm and elaborate this discovery. These measurements show that older stars similar to the sun tend to become brighter as their magnetic activity level increases, just as the sun does during its 11-year activity cycle. Younger stars, however, tend to become fainter as their magnetic activity level increases. This contrasting behavior suggests that the balance between the competing phenomena that influence solar brightness variability has shifted during the sun's lifetime.
The Loma Prieta, California, Earthquake: An Anticipated Event
Authors:   U.S. Geological Survey Staff
Published: October 2006

The first major earthquake on the San Andreas fault since 1906 fulfilled a long-term forecast for its rupture in the southern Santa Cruz Mountains. Severe damage occurred at distances of up to 100 kilometers from the epicenter in areas underlain by ground known to be hazardous in strong earthquakes. Stronger earthquakes will someday strike closer to urban centers in the United States, most of which also contain hazardous ground. The Loma Prieta earthquake demonstrated that meaningful predictions can be made of potential damage patterns and that, at least in well-studied areas, long-term forecasts can be made of future earthquake locations and magnitudes. Such forecasts can serve as a basis for action to reduce the threat major earthquakes pose to the United States.
Direct Observation and Analysis of CuO
2
Shear Defects in La
2-x
Sr
x
CuO
4
Authors: Gai Pratibha L. , McCarron Eugene M.
Published: October 2006

Direct observations of CuO
2
sheet defect structures in superconducting La

2-
x

Sr

x

CuO
4
, with
x
in the range 0.05 ≤
x
≤ 0.15, are reported. Electron microscopy shows that extended line defects are generated in {010} planes, along <206> crystallographic directions, by a pure shear mechanism along the edge of the octahedral copper-oxygen units. The line defects are partial screw dislocations, with characteristic displacement vectors of the type <(
a
/2), 0, (
c
/6)>, bounding the stacking faults. The existence of this type of defect demonstrates that there is an oxygen deficiency within the CuO
2
layers. However, unlike the open ReO
3
type-related structures, the packing density of the K
2
NiF
4
structure necessarily requires that anion defects be accompanied by the loss of cations of the A type (lanthanum, strontium). Under identical synthesis conditions, no defects are observed in the parent compound La
2
CuO
4
.
Stereochemistry of RNA Cleavage by the
Tetrahymena
Ribozyme and Evidence that the Chemical Step Is Not Rate-Limiting
Authors: McSwiggen James A. , Cech Thomas R.
Published: October 2006

The intervening sequence of the ribosomal RNA precursor of
Tetrahymena
is a catalytic RNA molecule, or ribozyme. Acting as a sequence-specific endoribonuclease, it cleaves single-stranded RNA substrates with concomitant addition of guanosine. The chemistry of the reaction has now been studied by introduction of a single phosphorothioate in the substrate RNA at the cleavage site. Kinetic studies show no significant effect of this substitution on
k
cat
(rate constant) or
K
m
(Michaelis constant), providing evidence that some step other than the chemical step is rate-limiting. Product analysis reveals that the reaction proceeds with inversion of configuration at phosphorus, consistent with an in-line, S
N
2 (P) mechanism. Thus, the ribozyme reaction is in the same mechanistic category as the individual displacement reactions catalyzed by protein nucleotidyltransferases, phosphotransferases, and nucleases.
Prevention of Translational Frameshifting by the Modified Nucleoside 1-Methylguanosine
Authors: Björk Glenn R. , Wikström P. Mikael , Byström Anders S.
Published: October 2006

The methylated nucleoside 1-methylguanosine (m
1
G) is present next to the 3′ end of the anticodon (position 37) in all transfer RNAs (tRNAs) that read codons starting with C except in those tRNAs that read CAN codons. All of the three proline tRNA species, which read CCN codons in
Salmonella typhimurium
, have been sequenced and shown to contain m
1
G in position 37. A mutant of
S. typhimurium
that lacks m
1
G in its tRNA when grown at temperatures above 37°C, has now been isolated. The mutation (
trmD3
) responsible for this methylation deficiency is in the structural gene (
trmD
) for the tRNA(m
1
G37)methyltransferase. Therefore, the three proline tRNAs in the
trmD3
mutant have an unmodified guanosine at position 37. Furthermore, the
trmD3
mutation also causes at least one of the tRNA
Pro
species to frequently shift frame when C's are present successively in the message. Thus, m
1
G appears to prevent frameshifting. The data from eubacteria apply to both eukaryotes and archaebacteria.
Persistence of Abnormal Chloride Conductance Regulation in Transformed Cystic Fibrosis Epithelia
Authors: Jetten Anton M. , Yankaskas James R. , Stutts M. Jackson , Willumsen Niels J. , Boucher Richard C.
Published: October 2006

An airway epithelial cell line (CF/T43) was developed by infecting cultured airway epithelial cells from patients with cystic fibrosis (CF) with the pZIPneoSV(X)1/SV40T retrovirus and selecting for G418 resistance and ion transport properties. The distinctive chloride secretory phenotypes of the CF cell line CF/T43 and a normal cell line (NL/T4) were not perturbed by SV40T-induced cell transformation. Epithelial cell lines generated from CF cells with the SV40T gene can be used to test candidate CF genes and to evaluate the molecular mechanisms responsible for the CF phenotype.
Adenylyl Cyclase Amino Acid Sequence: Possible Channel- or Transporter-Like Structure
Authors: Krupinski John , Coussen Françoise , Bakalyar Heather A. , Tang Wei-Jen , Feinstein Paul G. , Orth Kim , Slaughter Clive , Reed Randall R. , Gilman Alfred G.
Published: October 2006

Complementary DNA's that encode an adenylyl cyclase were isolated from a bovine brain library. Most of the deduced amino acid sequence of 1134 residues is divisible into two alternating sets of hydrophobic and hydrophilic domains. Each of the two large hydrophobic domains appears to contain six transmembrane spans. Each of the two large hydrophilic domains contains a sequence that is homologous to a single cytoplasmic domain of several guanylyl cyclases; these sequences may represent nucleotide binding sites. An unexpected topographical resemblance between adenylyl cyclase and various plasma membrane channels and transporters was observed. This structural complexity suggests possible, unappreciated functions for this important enzyme.
In Vitro Transcription Enhancement by Purified Derivatives of the Glucocorticoid Receptor
Authors: Freedman Leonard P. , Yoshinaga Steven K. , Vanderbilt Jeff N. , Yamamoto Keith R.
Published: October 2006

Mammalian glucocorticoid receptors enhance transcription from linked promoters by binding to glucocorticoid response element (GRE) DNA sequences. Understanding the mechanism of receptor action will require biochemical studies with purified components. Enhancement was observed in vitro with derivatives of the receptor that were expressed in
Escherichia coli
, purified, and added to a cell-free extract from
Drosophila
embryo nuclei. Transcription from promoters linked to one or multiple GREs was selectively enhanced by as much as six times. The effect was weaker with only one GRE, and enhancement was abolished by a point mutation that inactivates the GRE in vivo.
Increase in the Stratospheric Background Sulfuric Acid Aerosol Mass in the Past 10 Years
Authors: Hofmann D. J.
Published: October 2006

Data obtained from measurements of the stratospheric aerosol at Laramie, Wyoming (41°N), indicate that the background or nonvolcanic stratospheric sulfuric acid aerosol mass at northern mid-latitudes has increased by about 5 ± 2 percent per year during the past 10 years. Whether this increase is natural or anthropogenic could not be determined at this time because of inadequate information on sulfur sources, in particular, carbonyl sulfide, which is thought to be the dominant nonvolcanic source of stratospheric sulfuric acid vapor. An increase in stratospheric sulfate levels has important climatic implications as well as heterogeneous chemical effects that may alter the concentration of stratospheric ozone.
North-South Contraction of the Mojave Block and Strike-Slip Tectonics in Southern California
Authors: Bartley J. M. , Glazner A. F. , Schermer E. R.
Published: October 2006

The Mojave block of southern California has undergone significant late Cenozoic north-south contraction. This previously unappreciated deformation may account for part of the discrepancy between neotectonic and plate-tectonic estimates of Pacific-North American plate motion, and for part of the Big Bend in the San Andreas fault. In the eastern Mojave block, contraction is superimposed on early Miocene crustal extension. In the western Mojave block, contractional folds and reverse faults have been mistaken for extensional structures. The three-dimensional complexity of the contractional structures may mean that rigid-block tectonic models of the region based primarily on paleomagnetic data are unreliable.
Influence of Environmental Quality on Pollen Competitive Ability in Wild Radish
Authors: Young Helen J. , Stanton Maureen L.
Published: October 2006

Pollen of
Raphanus raphanistrum
produced under low nutrient conditions sired fewer seeds than pollen produced under better conditions when the two types were applied on a stigma together. No difference was seen in single-donor crosses. Male mating success can be strongly influenced by the environmental conditions of pollen-bearing plants, a factor overlooked in studies of plant reproductive biology and in standard quantitative genetic crossing designs, where effects of male parent are equated with heritable genetic variation.