bluuebunny/crossref_metadata_2025 huggingface dataset:
G Protein Activation of a Hormone-Stimulated Phosphatase in Human Tumor Cells
Authors: Pan Ming Gui , Florio Tullio , Stork Philip J. S.
Published: October 2006

The growth-inhibiting peptide hormone somatostatin stimulates phosphotyrosine phosphatase activity in the human pancreatic cell line MIA PaCa-2. This hormonal activation was mediated by a pertussis toxin-sensitive guanosine 5′-triphosphate-binding protein (G protein) in the membranes of these cells. Activation of this G protein by somatostatin stimulated the dephosphorylation of exogenous epidermal growth factor receptor prepared from A-431 cells in vitro. This pathway may mediate the antineoplastic action of somatostatin in these cells and in human tumors and could represent a general mechanism of G protein coupling that is utilized by normal cells in the hormonal control of cell growth.
In Vivo Modulation of Cytolytic Activity and Thy-1 Expression In TCR-γδ
+
Intraepithelial Lymphocytes
Authors: Lefrancois Leo , Goodman Thomas
Published: October 2006

Although the functional aspects of the αβ T cell antigen receptor (TCR) found on most peripheral T cells are well described, the function of the γδ TCR remains unclear. Murine intraepithelial lymphocytes (IEL) of the small intestine are CD8
+
, express the γδ TCR, and are constitutively lytic. Fresh IEL from germ-free mice had no lytic activity. Moreover, whereas IEL from normal mice are 30 to 50 percent Thy-1
+
, IEL from germ-free did not express Thy-1. Acclimation of germ-free mice to nonsterile conditions resulted in the generation of Thy-1
+
IEL and induction of lytic activity. Thus CD8
+
TCR-γδ IEL were regulated by externally derived stimuli via a specific functional interaction between IEL and gut-associated antigens.
Allelotype of Colorectal Carcinomas
Authors: Vogelstein Bert , Fearon Eric R. , Kern Scott E. , Hamilton Stanley R. , Preisinger Ann C. , Nakamura Yusuke , White Ray
Published: October 2006

To examine the extent and variation of allelic loss in a common adult tumor, polymorphic DNA markers were studied from every nonacrocentric autosomal arm in 56 paired colorectal carcinoma and adjacent normal colonic mucosa specimens. This analysis was termed an allelotype, in analogy with a karyotype. Three major conclusions were drawn from this analysis: (i) Allelic deletions were remarkably common; one of the alleles of each polymorphic marker tested was lost in at least some tumors, and some tumors lost more than half of their parental alleles. (ii) In addition to allelic deletions, new DNA fragments not present in normal tissue were identified in five carcinomas; these new fragments contained repeated sequences of the variable number of tandem repeat type. (iii) Patients with more than the median percentage of allelic deletions had a considerably worse prognosis than did the other patients, although the size and stage of the primary tumors were very similar in the two groups. In addition to its implications concerning the genetic events underlying tumorigenesis, tumor allelotype may provide a molecular tool for improved estimation of prognosis in patients with colorectal cancer.
Evidence for Retrograde Lithospheric Subduction on Venus
Authors: Sandwell David T. , Schubert Gerald
Published: October 2006

Annular moats and outer rises around large Venus coronae such as Artemis, Latona, and Eithinoha are similar in arcuate planform and topography to the trenches and outer rises of terrestrial subduction zones. On Earth, trenches and outer rises are modeled as the flexural response of a thin elastic lithosphere to the bending moment of the subducted slab; this lithospheric flexure model also accounts for the trenches and outer rises outboard of the major coronae on Venus. Accordingly, it is proposed that retrograde lithospheric subduction may be occurring on the margins of the large Venus coronae while compensating back-arc extension is occurring in the expanding coronae interiors. Similar processes may be taking place at other deep arcuate trenches or chasmata on Venus such as those in the Dali-Diana chasmata area of eastern Aphrodite Terra.
An Animal Model for Cystic Fibrosis Made by Gene Targeting
Authors: Snouwaert John N. , Brigman Kristen K. , Latour Anne M. , Malouf Nadia N. , Boucher Richard C. , Smithies Oliver , Koller Beverly H.
Published: October 2006

Cystic fibrosis results from defects in the gene encoding a cyclic adenosine monophosphate-dependent chloride ion channel known as the cystic fibrosis transmembrane conductance regulator (CFTR). To create an animal model for cystic fibrosis, mice were generated from embryonic stem cells in which the CFTR gene was disrupted by gene targeting. Mice homozygous for the disrupted gene display many features common to young human cystic fibrosis patients, including failure to thrive, meconium ileus, alteration of mucous and serous glands, and obstruction of glandlike structures with inspissated eosinophilic material. Death resulting from intestinal obstruction usually occurs before 40 days of age.
Mutation of the POU-Specific Domain of Pit-1 and Hypopituitarism Without Pituitary Hypoplasia
Authors: Pfäffle R. W. , DiMattia G. E. , Parks J. S. , Brown M. R. , Wit J. M. , Jansen M. , Van der Nat H. , Van den Brande J. L. , Rosenfeld M. G. , Ingraham H. A.
Published: October 2006

A point mutation in the POU-specific portion of the human gene that encodes the tissue-specific POU-domain transcription factor, Pit-1, results in hypopituitarism, with deficiencies of growth hormone, prolactin, and thyroid-stimulating hormone. In two unrelated Dutch families, a mutation in Pit-1 that altered an alanine in the first putative α helix of the POU-specific domain to proline was observed. This mutation generated a protein capable of binding to DNA response elements but unable to effectively activate its known target genes, growth hormone and prolactin. The phenotype of the affected individuals suggests that the mutant Pit-1 protein is competent to initiate other programs of gene activation required for normal proliferation of somatotrope, lactotrope, and thyrotrope cell types. Thus, a mutation in the POU-specific domain of Pit-1 has a selective effect on a subset of
Pit-1
target genes.
Defective Epithelial Chloride Transport in a Gene-Targeted Mouse Model of Cystic Fibrosis
Authors: Clarke Lane L. , Grubb Barbara R. , Gabriel Sherif E. , Smithies Oliver , Koller Beverly H. , Boucher Richard C.
Published: October 2006

The cystic fibrosis transmembrane conductance regulator (CFTR) gene encodes an adenosine 3′,5′-monophosphate (cyclic AMP)—activated chloride channel. In cystic fibrosis (CF) patients, loss of CFTR function because of a genetic mutation results in defective cyclic AMP—mediated chloride secretion across epithelia. Because of their potential role as an animal model for CF, mice with targeted disruption of the murine CFTR gene [CFTR(-/-)] were tested for abnormalities in epithelial chloride transport. In both freshly excised tissue from the intestine and in cultured epithelia from the proximal airways, the cyclic AMP—activated chloride secretory response was absent in CFTR(-/-) mice as compared to littermate controls. Thus, disruption of the murine CFTR gene results in the chloride transport abnormalities predicted from studies of human CF epithelia.
Tumor Suppressor Genes: The Puzzle and the Promise
Authors: Sager Ruth
Published: October 2006

Tumor suppressor genes are wild-type alleles of genes that play regulatory roles in cell proliferation, differentiation, and other cellular and systemic processes. It is their loss or inactivation that is oncogenic. The first evidence of tumor suppressor genes appeared in the early 1970s, but only within the past few years has a wealth of new information illuminated the central importance of these genes. Two or more different suppressor genes may be inactivated in the same tumors, and the same suppressors may be inactive in different tumor types (for example, lung, breast, and colon). The suppressor genes already identified are involved in cell cycle control, signal transduction, angiogenesis, and development, indicating that they contribute to a broad array of normal and tumor-related functions. It is proposed that tumor suppressor genes provide a vast untapped resource for anticancer therapy.
Two Distinct Populations of Calcium Channels in a Clonal Line of Pituitary Cells
Authors: Armstrong C. M. , Matteson D. R.
Published: October 2006

The whole-cell variant of the patch clamp technique was used to study calcium channels in GH3 cells. Two distinct populations of calcium channels, first recognized from their closing kinetics, were observed. The slowly closing channels are activated in a relatively negative voltage range and are inactivated within 100 milliseconds. They conduct barium and calcium about equally well. The fast closing channels are activated at more positive voltages, are not inactivated during a 100-millisecond pulse, conduct barium in preference to calcium, and are activated slightly more rapidly than the slowly closing channels.
Myosin: A Link Between Streptococci and Heart
Authors: Krisher Karen , Cunningham Madeleine W.
Published: October 2006

Murine monoclonal antibodies to
Streptococcus pyogenes
reacted with skeletal muscle myosin. High molecular weight proteins in extracts of human heart tissue that reacted with an antibody to
S. pyogenes
also reacted with a monoclonal antibody to ventricular myosin. Adsorption of the antibody to streptococci with
S. pyogenes
simultaneously removed reactivity of the antibody for either
S. pyogenes
or myosin. These results indicate that myosin shares immunodeterminants with a component of
S. pyogenes
.
Nucleotide Sequence and Expression of an AIDS-Associated Retrovirus (ARV-2)
Authors: Sanchez-Pescador Ray , Power Michael D. , Barr Philip J. , Steimer Kathelyn S. , Stempien Michelle M. , Brown-Shimer Sheryl L. , Gee Wendy W. , Renard Andre , Randolph Anne , Levy Jay A. , Dina Dino , Luciw Paul A.
Published: October 2006

The nucleotide sequence of molecular clones of DNA from a retrovirus, ARV-2, associated with the acquired immune deficiency syndrome (AIDS) was determined. Proviral DNA of ARV-2 (9737 base pairs) has long terminal repeat structures (636 base pairs) and long open reading frames encoding
gag
(506 codons),
pol
(1003 codons), and
env
(863 codons) genes. Two additional open reading frames were identified. Significant amino acid homology with several other retroviruses was noted in the predicted product of
gag
and
pol
, but ARV-2 was as closely related to murine and avian retroviruses as it was to human T-cell leukemia viruses (HTLV-I and HTLV-II). By means of an SV-40 vector in transfected simian cells, the cloned
gag
and
env
genes of ARV-2 were shown to express viral proteins.
Microbial Control of Silicate Weathering in Organic-Rich Ground Water
Authors: Hiebert Franz K. , Bennett Philip C.
Published: October 2006

An in situ microcosm study of the influence of surface-adhering bacteria on silicate diagenesis in a shallow petroleum-contaminated aquifer showed that minerals were colonized by indigenous bacteria and chemically weathered at a rate faster than theoretically predicted. Feldspar and quartz fragments were placed in anoxic, organic-rich ground water, left for 14 months, recovered, and compared to unreacted controls with scanning electron microscopy. Ground-water geochemistry was characterized before and after the experiment. Localized mineral etching probably occurred in a reaction zone at the bacteria-mineral interface where high concentrations of organic acids, formed by bacteria during metabolism of hydrocarbon, selectively mobilized silica and aluminum from the mineral surface.
Regulation of the Amount of Starch in Plant Tissues by ADP Glucose Pyrophosphorylase
Authors: Stark David M. , Timmerman Kurt P. , Barry Gerard F. , Preiss Jack , Kishore Ganesh M.
Published: October 2006

Starch, a major storage metabolite in plants, positively affects the agricultural yield of a number of crops. Its biosynthetic reactions use adenosine diphosphate glucose (ADPGlc) as a substrate; ADPGlc pyrophosphorylase, the enzyme involved in ADPGlc formation, is regulated by allosteric effectors. Evidence that this plastidial enzyme catalyzes a rate-limiting reaction in starch biosynthesis was derived by expression in plants of a gene that encodes a regulatory variant of this enzyme. Allosteric regulation was demonstrated to be the major physiological mechanism that controls starch biosynthesis. Thus, plant and bacterial systems for starch and glycogen biosynthesis are similar and distinct from yeast and mammalian systems, wherein glycogen synthase has been demonstrated to be the rate-limiting regulatory step.
Age and Duration of Weathering by
40
K-
40
Ar and
40
Ar/
39
Ar Analysis of Potassium-Manganese Oxides
Authors: Vasconcelos Paulo M. , Becker Tim A. , Renne Paul R. , Brimhall George H.
Published: October 2006

Supergene cryptomelane [K
1–2
(Mn
3+
Mn
4+
)
8
O
16
⋅ χH
2
O] samples from deeply weathered pegmatites in southeastern Brazil subjected to
40
K-
40
Ar and
40
Ar/
39
Ar analysis yielded
40
K-
40
Ar dates ranging from 10.1 ± 0.5 to 5.6 ± 0.2 Ma (million years ago). Laser-probe
40
Ar/
39
Ar step-heating of the two most disparate samples yielded plateau dates of 9.94 ± 0.05 and 5.59 ± 0.10 Ma, corresponding, within 2 σ, to the
40
K-
40
Ar dates. The results imply that deep weathering profiles along the eastern Brazilian margin do not reflect present climatic conditions but are the result of a long-term process that was already advanced by the late Miocene. Weathering ages predate pulses of continental sedimentation along the eastern Brazilian margin and suggest that there was a time lag between weathering and erosion processes and sedimentation processes.
Mercury Radar Imaging: Evidence for Polar Ice
Authors: Slade Martin A. , Butler Bryan J. , Muhleman Duane O.
Published: October 2006

The first unambiguous full-disk radar mapping of Mercury at 3.5-centimeter wavelength, with the Goldstone 70-meter antenna transmitting and 26 antennas of the Very Large Array receiving, has provided evidence for the presence of polar ice. The radar experiments, conducted on 8 and 23 August 1991, were designed to image the half of Mercury not photographed by Mariner 10. The orbital geometry allowed viewing beyond the north pole of Mercury; a highly reflective region was clearly visible on the north pole during both experiments. This polar region has areas in which the circular polarization ratio (μ
c
) was 1.0 to 1.4; values < ∼0.1 are typical for terrestrial planets. Such high values of μ
c
have hitherto been observed in radar observations only from icy regions of Mars and icy outer planet satellites.
The Thermal Stability of Water Ice at the Poles of Mercury
Authors: Paige David A. , Wood Stephen E. , Vasavada Ashwin R.
Published: October 2006

Recent radar observations of Mercury have revealed the presence of anomalous radar reflectivity and polarization features near its north and south poles. Thermal model calculations show that, despite Mercury's proximity to the sun, the temperatures of flat, low-reflectivity surfaces at Mercury's poles are not expected to exceed 167 kelvin. The locations of the anomalous polar radar features appear to be correlated with the locations of large, high-latitude impact craters. Maximum surface temperatures in the permanently shadowed regions of these craters are expected to be significantly colder, as low as 60 kelvin in the largest craters. These results are consistent with the presence of water ice, because at temperatures lower than 112 kelvin, water ice should be stable to evaporation over time scales of billions of years.
Managing Insect Resistance to
Bacillus thuringiensis
Toxins
Authors: McGaughey William H. , Whalon Mark E.
Published: October 2006

Bacillus thuringiensis
(
B.t.
) δ-endotoxins provide an alternative to chemical insecticides for controlling many species of pest insects. Recent biotechnological developments offer the promise of even greater use of
B.t.
toxins in genetically transformed pest-resistant crops. However, the discovery that insects can adapt to these toxins raises concerns about the long-term usefulness of
B.t.
toxins. Several methods for managing the development of resistance to
B.t.
toxins have been suggested, but none of these approaches offer clear advantages in all situations.
Himalayan Tectonics, Weathering Processes, and the Strontium Isotope Record in Marine Limestones
Authors: Edmond J. M.
Published: October 2006

The time evolution of the isotopic composition of seawater strontium (the ratio of strontium-87 to strontium-86) over the last 500 million years has the form of an asymmetric trough. The values are highest in the Cambrian and Recent (0.7091) and lowest in the Jurassic (0.7067). Superimposed on this trend are a number of smaller oscillations. Consideration of the geochemical cycle of strontium and the dynamics of weathering shows that only Himalayan-style continental collisions can influence the isotope ratio on the scale observed. The contemporary Himalayan orogeny is by far the largest since the late Precambrian Pan-African event that produced the high in the Cambrian.
Terrestrial Carbon and Nitrogen Isotopic Ratios from Cretaceous-Tertiary Boundary Nanodiamonds
Authors: Gilmour I. , Russell S. S. , Arden J. W. , Lee M. R. , Franchi I. A. , Pillinger C. T.
Published: October 2006

One hypothesis for the origin of the nanometer-size diamonds found at the Cretaceous-Tertiary (K-T) boundary is that they are relict interstellar diamond grains carried by a postulated asteroid. The
13
C/
12
C and
15
N/
14
N ratios of the diamonds from two sites in North America, however, show that the diamonds are two component mixtures differing in carbon and nitrogen isotopic composition and nitrogen abundance. Samples from a site from Italy show no evidence for either diamond component. All the isotopic signatures obtained from the K-T boundary are material well distinguished from known meteoritic diamonds, particularly the fine-grain interstellar diamonds that are abundant in primitive chondrites. The K-T diamonds were most likely produced during the impact of the asteroid with Earth or in a plasma resulting from the associated fireball.
Electronic, Magnetic, and Geometric Structure of Metallo-Carbohedrenes
Authors: Reddy B. V. , Khanna S. N. , Jena P.
Published: October 2006

The energetics and the electronic, magnetic, and geometric structure of the metallocarbohedrene Ti
8
C
12
have been calculated self-consistently in the density functional formulation. The structure of Ti
8
C
12
is a distorted dodecahedron with a binding energy of 6.1 electron volts per atom. The unusual stability is derived from covalent-like bonding between carbon atoms and between titanium and carbon atoms with no appreciable interaction between titanium atoms. The density of states at the Fermi energy is high and is derived from a strong hybridization between titanium 3
d
and carbon
sp
electrons. Titanium sites carry a small magnetic moment of 0.35 Bohr magneton per atom and the cluster is only weakly magnetic.
The Chaotic Obliquity of Mars
Authors: Touma Jihad , Wisdom Jack
Published: October 2006

Numerical integration of the rotation of Mars shows that the obliquity of Mars undergoes large chaotic variations. These variations occur as the system evolves in the chaotic zone associated with a secular spin-orbit resonance.
Turning Down the Heat: Design and Mechanism in Solid-State Synthesis
Authors: Stein Andreas , Keller Steven W. , Mallouk Thomas E.
Published: October 2006

Solid-state compounds have historically been prepared through high-temperature solid-solid reactions. New mechanistic understanding of these reactions suggests possible routes to metastable compositions and structures as well as to thermodynamically stable, low-temperature phases that decompose at higher temperatures. Intermediate-temperature synthetic techniques, including flux and hydrothermal methods, as well as low-temperature intercalation and coordination reactions, have recently been developed and have been used to prepare unprecedented materials with interesting electronic, optical, and catalytic properties. The trend in modern solid-state synthesis resembles increasingly the approach used in small-molecule chemistry, in the sense that attention to reaction mechanism and the use of molecular building blocks result in an ability to prepare new materials of designed structure.
A Decipherment of Epi-Olmec Hieroglyphic Writing
Authors: Justeson John S. , Kaufman Terrence
Published: October 2006

The decipherment of part of the epi-Olmec script of ancient Mexico, which yields the earliest currently readable texts in Mesoamerica, has been achieved over the last 2 years. This was made possible by the discovery of a stela with a long inscription at La Mojarra, Veracruz, Mexico, in 1986. This decipherment is based on both a reconstruction of the early stages of languages spoken in the region and semantic clues provided by comparison with cultural practices and other script traditions of early southern Mesoamerica. Summarized here is the current state of the phonetic decipherment, the methods used for the decipherment, and results concerning the epi-Olmec language and script. The language identified in the inscriptions is pre—proto-Zoquean, the ancestor of four languages now spoken in the states of Veracruz, Tabasco, Chiapas, and Oaxaca. The decipherment contributes to knowledge of early Mixe-Zoquean language history. The script is more closely related to Mayan hieroglyphic writing than to other early Mesoamerican scripts, and this relation is closer than previously recognized.
Silica Precipitation in Fractures and the Evolution of Permeability in Hydrothermal Upflow Zones
Authors: Lowell Robert P. , Van Cappellen Philippe , Germanovich Leonid N.
Published: October 2006

Analytical models are used to compare the rates at which an isolated fracture and vertical, parallel fracture sets in hydrothermal upflow zones can be closed by silica precipitation and thermoelastic stress. Thermoelastic sealing is an order of magnitude faster than sealing by silica precipitation. In vertical fracture sets, both the amount of silica precipitation resulting from cooling and the total thermal expansion of the country rock may be insufficient to seal cracks at depth. These crack systems may ultimately close because the pressure dependence of silica solubility maintains precipitation during upflow even after the temperature gradient vanishes.
Seismicity Remotely Triggered by the Magnitude 7.3 Landers, California, Earthquake
Authors: Hill D. P. , Reasenberg P. A. , Michael A. , Arabaz W. J. , Beroza G. , Brumbaugh D. , Brune J. N. , Castro R. , Davis S. , dePolo D. , Ellsworth W. L. , Gomberg J. , Harmsen S. , House L. , Jackson S. M. , Johnston M. J. S. , Jones L. , Keller R. , Malone S. , Munguia L. , Nava S. , Pechmann J. C. , Sanford A. , Simpson R. W. , Smith R. B. , Stark M. , Stickney M. , Vidal A. , Walter S. , Wong V. , Zollweg J.
Published: October 2006

The magnitude 7.3 Landers earthquake of 28 June 1992 triggered a remarkably sudden and widespread increase in earthquake activity across much of the western United States. The triggered earthquakes, which occurred at distances up to 1250 kilometers (17 source dimensions) from the Landers mainshock, were confined to areas of persistent seismicity and strike-slip to normal faulting. Many of the triggered areas also are sites of geothermal and recent volcanic activity. Static stress changes calculated for elastic models of the earthquake appear to be too small to have caused the triggering. The most promising explanations involve nonlinear interactions between large dynamic strains accompanying seismic waves from the mainshock and crustal fluids (perhaps including crustal magma).
Paleoatmospheric Signatures in Neogene Fossil Leaves
Authors: Van Der Burgh Johan , Visscher Henk , Dilcher David L. , Kürschner Wolfram M.
Published: October 2006

An increase in the atmospheric carbon dioxide (CO
2
) concentration results in a decrease in the number of leaf stomata. This relation is known both from historical observations of vegetation over the past 200 years and from experimental manipulations of microenvironments. Evidence from stomatal frequencies of fossil
Quercus petraea
leaves indicates that this relation can be applied as a bioindicator for changes in paleoatmospheric CO
2
concentrations during the last 10 million years. The data suggest that late Neogene CO
2
concentrations fluctuated between about 280 and 370 parts per million by volume.
Ecological Roulette: The Global Transport of Nonindigenous Marine Organisms
Authors: Cariton James T. , Geller Jonathan B.
Published: October 2006

Ocean-going ships carry, as ballast, seawater that is taken on in port and released at subsequent ports of call. Plankton samples from Japanese ballast water released in Oregon contained 367 taxa. Most taxa with a planktonic phase in their life cycle were found in ballast water, as were all major marine habitat and trophic groups. Transport of entire coastal planktonic assemblages across oceanic barriers to similar habitats renders bays, estuaries, and inland waters among the most threatened ecosystems in the world. Presence of taxonomically difficult or inconspicuous taxa in these samples suggests that ballast water invasions are already pervasive.
A 50,000-Year Record of Climate Oscillations from Florida and Its Temporal Correlation with the Heinrich Events
Authors: Grimm Eric C. , Jacobson George L. , Watts William A. , Hansen Barbara C. S. , Maasch Kirk A.
Published: October 2006

Oscillations of
Pinus
(pine) pollen in a 50,000-year sequence from Lake Tulane, Florida, indicate that there were major vegetation shifts during the last glacial cycle. Episodes of abundant
Pinus
populations indicate a climate that was more wet than intervening phases dominated by
Quercus
(oak) and
Ambrosia
-type (ragweed and marsh-elder). The
Pinus
episodes seem to be temporally correlated with the North Atlantic Heinrich events, which were massive, periodic advances of ice streams from the eastern margin of the Laurentide Ice Sheet. Possible links between the Tulane
Pinus
and Heinrich events include hemispheric cooling, the influences of Mississippi meltwater on sea-surface temperatures in the Gulf of Mexico, and the effects of North Atlantic thermohaline circulation on currents in the Gulf.
Surface Tension Measurements of Surface Freezing in Liquid Normal Alkanes
Authors: Wu X. Z. , Ocko B. M. , Sirota E. B. , Sinha S. K. , Deutsch M. , Cao B. H. , Kim M. W.
Published: October 2006

Surface tension measurements reveal surface freezing in liquid
n
-alkanes. A solid monolayer of molecules is found to exist up to 30°C above the bulk freezing point. This surface phase exists only for carbon numbers 14 <
n
≤ 50. The measured carbon number and temperature dependence of the surface tension is interpreted within a simple thermodynamical model based on known bulk latent heat data and surface energy considerations. The vanishing of the surface phase for
n
≤ 14 is a possible transition from surface freezing to surface melting behavior.
Hydrogen in Stishovite, with Implications for Mantle Water Content
Authors: Pawley Alison R. , McMillan Paul F. , Holloway John R.
Published: October 2006

Stishovite, the highest pressure polymorph of silicon dioxide, may be an important mineral in some regions of the Earth's mantle. Fourier transform infrared spectroscopy has been used to determine the hydrogen content of synthetic stishovite. The concentration of hydrogen depends on the aluminum content of the sample and reaches a maximum of 549 ± 23 hydrogen atoms per 10
6
silicon atoms for an Al
2
O
3
content of 1.51 percent by weight. Stishovite could be a storage site for water in deep subducting slabs and in regions of the mantle that are too hot for hydrous minerals to be stable.
Rhenium-Osmium Evidence for Regional Mineralization in Southwestern North America
Authors: McCandless T. E. , Ruiz J.
Published: October 2006

More than 40 base metal porphyry ore deposits in southwestern North America are associated with the Laramide orogeny (about 90 million to 50 million years ago). Rhenium-osmium dates on molybdenite, a rhenium-enriched sulfide common in many of the deposits, reveal that in individual deposits mineralization occurs near the final stages of magmatic activity irrespective of the time of inception, magnitude, or duration of magmatism. Deposits that differ widely in location and in the extent and timing of magmatism have nearly identical ages for mineralization. Rhenium-osmium-ages suggest that mineralization occurred during two distinct intervals from about 74 million to 70 million years ago and from 60 million to 55 million years ago. Most deposits that formed in the oldest interval are within the older Precambrian basement of northwestern Arizona, whereas the younger deposits are restricted to the younger Precambrian basement in southern Arizona and northern Mexico. Synchronous, widespread mineralization indicates that similar crust-mantle interaction occurred on a regional scale for ore deposits once thought to be the product of localized processes.
Discovery of Vapor Deposits in the Lunar Regolith
Authors: Keller Lindsay P. , McKay David S.
Published: October 2006

Lunar soils contain micrometer-sized mineral grains surrounded by thin amorphous rims. Similar features have been produced by exposure of pristine grains to a simulated solar wind, leading to the widespread belief that the amorphous rims result from radiation damage. Electron microscopy studies show, however, that the amorphous rims are compositionally distinct from their hosts and consist largely of vapor-deposited material generated by micrometeorite impacts into the lunar regolith. Vapor deposits slow the lunar erosion rate by solar wind sputtering, influence the optical properties of the lunar regolith, and may account for the presence of sodium and potassium in the lunar atmosphere.
Late Cretaceous Precessional Cycles in Double Time: A Warm-Earth Milankovitch Response
Authors: Park J. , D'Hondt S. L. , King J. W. , Gibson C.
Published: October 2006

Late Cretaceous climatic cycles are reflected in lithological and magnetic variations in carbonate sediments from South Atlantic Deep-Sea Drilling Project site 516F at a paleolatitude of roughly 30°S. Magnetic susceptibility cycles 20 to 60 centimeters in length appear to be controlled by the precession of the equinoxes. Cyclicity is particularly robust within a 24-meter interval in the lower Campanian, where overtone spectral peaks are observed as well as secondary susceptibility maxima within individual precession cycles. One model for this behavior is that sedimentation in the narrow Cretaceous South Atlantic was controlled by equatorial climate dynamics, with the precessional insolation signal rectified by the large land masses surrounding the ocean basin.
Activation of Floral Homeotic Genes in
Arabidopsis
Authors: Weigel Detlef , Meyerowitz Elliot M.
Published: October 2006

The identity of floral organs in
Arabidopsis thaliana
is determined by homeotic genes, which are expressed in specific regions of the developing flower. The initial activation of homeotic genes is accomplished at least in part by the products of two earlier acting genes with overlapping functions. These are the floral meristem—identity genes
LEAFY
and
APETALA1
. The requirements of
LEAFY
and
APETALA1
activity vary for different homeotic genes.
Anatomy of the Photodissociation Region in the Orion Bar
Authors: Tielens A. G. G. M. , Meixner M. M. , van der Werf P. P. , Bregman J. , Tauber J. A. , Stutzki J. , Rank D.
Published: October 2006

Much of the interstellar gas resides in photodissociation regions whose chemistry and energy balance is controlled by the flux of far-ultraviolet radiation upon them. These photons can ionize and dissociate molecules and heat the gas through the photoelectric effect working on dust grains. These regions have been extensively modeled theoretically, but detailed observational studies are few. Mapping of the prominent Orion Bar photodissociation region at wavelengths corresponding to the carbon-hydrogen stretching mode of polycyclic aromatic hydrocarbons, the 1-0 S(1) line of molecular hydrogen, and the
J
= 1-0 rotational line of carbon monoxide allows the penetration of the far-ultraviolet radiation into the cloud to be traced. The results strongly support the theoretical models and show conclusively that the incident far-ultraviolet radiation field, not shocks as has sometimes been proposed, is responsible for the emission in the Orion Bar.
Dissipation of Marine Stratiform Clouds and Collapse of the Marine Boundary Layer Due to the Depletion of Cloud Condensation Nuclei by Clouds
Authors: Ackerman Andrew S. , Toon Owen B. , Hobbs Peter V.
Published: October 2006

When the production of cloud condensation nuclei in the stratocumulus-topped marine boundary layer is low enough, droplet collisions can reduce concentrations of cloud droplet numbers to extremely low values. At low droplet concentrations a cloud layer can become so optically thin that cloud-top radiative cooling cannot drive vertical mixing. Under these conditions, model simulations indicate that the stratocumulus-topped marine boundary layer collapses to a shallow fog layer. Through this mechanism, marine stratiform clouds may limit their own lifetimes.
Laser Ablation and the Production of Polymer Films
Authors: Blanchet Graciela B. , Fincher C. R. , Jackson C. L. , Shah S. I. , Gardner K. H.
Published: October 2006

The formation of high-quality thin films of polytetrafluoroethylene (PTFE) is important in many applications ranging from material reinforcement to molecular electronics. Laser ablation, a technique widely used to deposit a variety of inorganic materials, can also be used as a simple and highly versatile method for forming thin polymer films. The data presented show that PTFE films can be produced on various supports by the evaporation of a solid PTFE target with a pulsed ultraviolet laser. The composition of the ablation plume suggests that PTFE ablation and subsequent film formation occur by way of a laser-induced pyrolitic decomposition with subsequent repolymerization. The polymer films produced by this method are composed of amorphous and highly crystalline regions, the latter being predominantly in a chain-folded configuration with the molecular axis aligned parallel to the substrate surface.
Mississippian Fossils from Southern Appalachian Metamorphic Rocks and Their Implications for Late Paleozoic Tectonic Evolution
Authors: Gastaldo Robert A. , Guthrie Gregory M. , Steltenpohl Mark G. , Gastaldo R. A. , Steltenpohl M. G.
Published: October 2006

Fossils of
Periastron reticulatum
Unger emended. Beck recovered from the Erin Slate of the Talladega slate belt of Alabama establish that these rocks have a Mississippian (Kinderhookian-Tournaisian) age. The Talladega slate belt, the southwestern extension of the western Blue Ridge belt, was interpreted to have been affected by regional dynamothermal metamorphism and coeval deformation as a result of the Acadian orogeny. This fossil find indicates that metamorphism and deformation of the Talladega belt occurred after the Early Carboniferous (Alleghanian), requiring a reevaluation of tectonic interpretations of the southernmost Appalachians.
Fire History and Climate Change in Giant Sequoia Groves
Authors: Swetnam Thomas W.
Published: October 2006

Fire scars in giant sequoia [
Sequoiadendron giganteum
(Lindley) Buchholz] were used to reconstruct the spatial and temporal pattern of surface fires that burned episodically through five groves during the past 2000 years. Comparisons with independent dendroclimatic reconstructions indicate that regionally synchronous fire occurrence was inversely related to yearly fluctuations in precipitation and directly related to decadal-to-centennial variations in temperature. Frequent small fires occurred during a warm period from about A.D. 1000 to 1300, and less frequent but more widespread fires occurred during cooler periods from about A.D. 500 to 1000 and after A.D. 1300. Regionally synchronous fire histories demonstrate the importance of climate in maintaining nonequilibrium conditions.
Lipid Tubules: A Paradigm for Molecularly Engineered Structures
Authors: Schnur Joel M.
Published: October 2006

The use of molecular self-assembly to fabricate microstructures suitable for advanced material development is described. Templating techniques that transform biomolecular self-assemblies into rugged and stable nano- and microstructures are described. By using a lipid-based microcylinder (tubule) as a paradigm, the path followed from research and development to emerging technological applications is detailed. This process includes modification of the lipid molecular structure, the formation and subsequent characterization of cylindrical microstructures, the use of these structures as templates for metallization, and the characterization and assessment of these hollow metal microcylinders for several potential applications.
Adhesive Electroless Metallization of Fluoropolymeric Substrates
Authors: Vargo Terrence G. , Gardella Joseph A. , Calvert Jeffrey M. , Chen Mu-San
Published: October 2006

A process for producing patterned metal deposits on fluoropolymeric substrates is described. A metal ion—chelating organosilane is chemisorbed by self-assembly onto a fluoropolymer surface after radio-frequency glow discharge plasma surface hydroxylation. Positional modulation of the surface hydrophobicity is illustrated by wetting. The silane covalently binds an aqueous palladium catalyst and subsequent electroless deposition yields homogeneous or patterned metal deposits that exhibit excellent adhesion to the fluoropolymer.
A
Salmonella
Locus that Controls Resistance to Microbicidal Proteins from Phagocytic Cells
Authors: Fields Patricia I. , Groisman Eduardo A. , Heffron Fred
Published: October 2006

Facultative intracellular pathogens pose an important health problem because they circumvent a primary defense mechanism of the host: killing and degradation by professional phagocytic cells. A gene of the intracellular pathogen
Salmonella typhimurium
that is required for virulence and intracellular survival was identified and shown to have a role in resistance to defensins and possibly to other microbicidal mechanisms of the phagocyte. This gene may prove to be a regulatory element in the expression of virulence functions.
Topology and Formation of Triple-Stranded H-DNA
Authors: Htun Han , Dahlberg James E.
Published: October 2006

Repeating copolymers of (dT-dC)

n

⋅(dA-dG)

n

sequences (TC⋅AG

n

) can assume a hinged DNA structure (H-DNA) which is composed of triple-stranded and single-stranded regions. A model for the formation of H-DNA is proposed, based on two-dimensional gel electrophoretic analysis of DNA's with different lengths of (TC⋅AG)

n

copolymers. In this model, H-DNA formation is initiated at a small denaturation bubble in the interior of the copolymer, which allows the duplexes on either side to rotate slightly and to fold back, in order to make the first base triplet. This nucleation establishes which of several nonequivalent H-DNA conformations is to be assumed by any DNA molecule, thereby trapping each molecule in one of several metastable conformers that are not freely interconvertible. Subsequently, the acceptor region spools up single-stranded polypyrimidines as they are released by progressive denaturation of the donor region; both the spooling and the denaturation result in relaxation of negative supercoils in the rest of the DNA molecule. From the model, it can be predicted that the levels of supercoiling of the DNA determine which half of the (dT-dC)

n

repeat is to become the donated third strand.
Class II MHC Molecules Are Specific Receptors for
Staphylococcus
Enterotoxin A
Authors: Mollick Joseph A. , Cook Richard G. , Rich Robert R.
Published: October 2006

T cell proliferation in response to stimulation with
Staphylococcus
enterotoxin A (SEA) requires accessory cells that express class II major histocompatibility complex (MHC) molecules. Murine fibroblasts transfected with genes encoding the α and β subunits of HLA-DR, DQ, or DP were used to show that the proliferative response of purified human T cells to SEA is dependent on class II molecules but is not restricted by the haplotype of the responder. Binding of fluoresceinated SEA to class II transfectants and precipitation of class II heterodimers with SEA-Sepharose show that the proliferative response is a result of SEA binding to class II molecules. The binding is specific for class II molecules and is independent of class II allotype or isotype. The ability of SEA to bind class II molecules may be a general characteristic of this class of antigens, now called "superantigens".
G
1
/S Transition in Normal Human T-Lymphocytes Requires the Nuclear Protein Encoded by c-
myb
Authors: Gewirtz Alan M. , Anfossi Giovanni , Venturelli Donatella , Valpreda Susanna , Sims Robert , Calabretta Bruno
Published: October 2006

Exposure of peripheral blood mononuclear cells (PBMC) to an 18-base c-
myb
antisense oligomer before mitogen or antigen stimulation resulted in almost complete inhibition of c-
myb
messenger RNA and protein synthesis and blockade of T lymphocyte proliferation. Expression of early and late activation markers, interleukin-2 receptor and transferrin receptor, respectively, by PBMC was unaffected by antisense oligomer exposure as was the expression of c-
myc
messenger RNA. In contrast, histone H3 messenger RNA levels and DNA content were selectively decreased. These results suggest that c-
myb
protein deprivation does not perturb T lymphocyte activation or early molecular events that may prepare the cell for subsequent proliferation. Rather, it appears to specifically block cells in late G
1
or early S phase of the cell cycle.
The Reservoir for HIV-1 in Human Peripheral Blood Is a T Cell That Maintains Expression of CD4
Authors: Schnittman Steven M. , Psallidopoulos Miltiades C. , Lane H. Clifford , Thompson Louis , Baseler Michael , Massari Ferdinand , Fox Cecil H. , Salzman Norman P. , Fauci Anthony S.
Published: October 2006

Human immunodeficiency virus type 1 (HIV-1) selectively infects cells expressing the CD4 molecule, resulting in substantial quantitative and qualitative defects in CD4
+
T lymphocyte function in patients with acquired immunodeficiency syndrome (AIDS). However, only a very small number of cells in the peripheral blood of HIV-1-infected individuals are expressing virus at any given time. Previous studies have demonstrated that in vitro infection of CD4
+
T cells with HIV-1 results in downregulation of CD4 expression such that CD4 protein is no longer detectable on the surface of the infected cells. In the present study, highly purified subpopulations of peripheral blood mononuclear cells (PBMCs) from AIDS patients were obtained and purified by fluorescence-automated cell sorting. They were examined with the methodologies of virus isolation by limiting dilution analysis, in situ hybridization, immunofluorescence, and gene amplification. Within PBMCs, HIV-1 was expressed in vivo predominantly in the T cell subpopulation which, in contrast to the in vitro observations, continued to express CD4. The precursor frequency of these HIV-1-expressing cells was about 1/1000 CD4
+
T cells. The CD4
+
T cell population contained HIV-1 DNA in all HIV-1-infected individuals studied and the frequency in AIDS patients was at least 1/100 cells. This high level of infection may be the primary cause for the progressive decline in number and function of CD4
+
T cells in patients with AIDS.
Kainic Acid Lesions of the Striatum Dissociate Amphetamine and Apomorphine Stereotypy: Similarities to Huntingdon's Chorea
Authors: Mason S. T. , Sanberg P. R. , Fibiger H. C.
Published: October 2006

Kainic acid lesion of cell bodies in the dorsal striatum enhanced the stereotypy-producing effects ofd-amphetamine without affecting the stereotypy produced by the direct receptor agonist apomorphine. This pattern of results parallels that found in patients suffering from Huntington's chorea, thus strengthening the parallels between the kainic acid animal model and the human disease state initially suggested on biochemical grounds. The present results further suggest a dissociation of the mechanisms involved in the production of stereotypy by these two drugs, perhaps in terms of differential involvement of the striato-nigral negative feedback loop.
Novel Sites of Expression of Functional Angiotensin II Receptors in the Late Gestation Fetus
Authors: Millan Monica A. , Carvallo Pilar , Izumi Shun-Ichiro , Zemel Sharon , Catt Kevin J. , Aguilera Greti
Published: October 2006

In the adult, the peptide hormone angiotensin II (AII) is primarily known as a regulator of circulatory homeostasis, but recent evidence also suggests a role in cell growth. This study of AII in late gestation rat fetuses revealed the unexpected presence of receptors in skeletal muscle and connective tissue, in addition to those in recognized adult target tissues. The AII receptors in this novel location decreased by 80 percent 1 day after birth and were almost undetectable in the adult. Studies in fetal skin fibroblasts showed that the receptors were coupled to phospholipid breakdown, with concomitant increases in inositol phosphate and cytosolic calcium. The abundance, timing of expression, and unique localization of functional AII receptors in the fetus suggest a role for AII in fetal development.
Spatial Selectivity of Rat Hippocampal Neurons: Dependence on Preparedness for Movement
Authors: Foster Tom .C , Castro Carl A. , McNaughton Bruce L.
Published: October 2006

The mammalian hippocampal formation appears to play a major role in the generation of internal representations of spatial relationships. In rats, this role is reflected in the spatially selective discharge of hippocampal pyramidal cells. The principal metric for coding spatial relationships might be the organism's own movements in space, that is, the spatial relationship between two locations is coded in terms of the movements executed in getting from one to the other. Thus, information from the motor programming systems (or "motor set") may contribute to coding of spatial location by hippocampal neurons. Spatially selective discharge of hippocampal neurons was abolished under conditions of restraint in which the animal had learned that locomotion was impossible. Therefore, hippocampal neuronal activity may reflect the association of movements with their spatial consequences.
Histone H5 in the Control of DNA Synthesis and Cell Proliferation
Authors: Sun Jian-Min , Wiaderkiewicz Ryszard , Ruiz-Carrillo Adolfo
Published: October 2006

The linker histones (H1, H5, H1°) are involved in the condensation of chromatin into the 30-nanometer fiber. This supranucleosome organization correlates with the resting state of chromatin, and it is therefore possible that the linker histones play an active role in the control of chromatin activity. The effect of H5 has been directly determined by expression of an inducible transfected H5 gene in rat sarcoma cells, which do not produce H5. Transfection resulted in the reversible inhibition of DNA replication and arrest of cells in G
1
, at which time H5 concentrations approached that of terminally differentiated avian erythrocytes. The arrest of proliferation was accompanied by specific changes in gene expression probably related to the cell cycle block. The selectivity of these effects suggest that H5 plays an active role in the control of DNA replication and cell proliferation.