bluuebunny/crossref_metadata_2025 huggingface dataset:
The CML-Specific P210
bcr
/
abl
Protein, Unlike v-
abl
, Does Not Transform NIH/3T3 Fibroblasts
Authors: Daley George Q. , McLaughlin Jami , Witte Owen N. , Baltimore David
Published: October 2006

The v-
abl
oncogene of the Abelson murine leukemia virus (A-MuLV) is known to efficiently transform NIH/3T3 fibroblasts in vitro and to cause an acute lymphosarcoma in susceptible murine hosts. The role of its relative, the
bcr
/
abl
gene product, in the etiology of human chronic myelogenous leukemia (CML) remains speculative. To assess the transforming properties of the
bcr
/
abl
gene product, complementary DNA clones encoding the CML-specific P210
bcr
/
abl
protein were expressed in NIH/3T3 fibroblasts. In contrast to the v-
abl
oncogene product P160, the P210
bcr
/
abl
gene product did not transform NIH/3T3 cells. Cell lines were isolated that expressed high levels of the P210
bcr
/
abl
protein but were morphologically normal. During the course of these experiments, a transforming recombinant of
bcr
/
abl
was isolated which fuses
gag
determinants derived from helper virus to the NH
2
-terminus of the
bcr
/
abl
protein. This suggests that a property of viral
gag
sequences, probably myristylation-dependent membrane localization, must be provided to
bcr
/
abl
for it to transform fibroblasts.
Rapid Change in the Symbolic Functioning of Very Young Children
Authors: DeLoache Judy S.
Published: October 2006

A remarkable difference in the understanding of the symbolic relation between a scale model and the larger space that it represented was displayed by two age groups of young children. Three-year-old children who observed an object being hidden in a model knew where to find an analogous object hidden in the corresponding location in a room, but 2.5-year-old children did not. The success of the group of older children reveals an advance in their cognitive flexibility: they think of a model in two ways at the same time--both as the thing itself and as a symbol for something else.
GaAs Clusters in the Quantum Size Regime: Growth on High Surface Area Silica by Molecular Beam Epitaxy
Authors: Sandroff C. J. , Harbison J. P. , Ramesh R. , Andrejco M. J. , Hegde M. S. , Hwang D. M. , Chang C. C. , Vogel E. M.
Published: October 2006

Molecular beam epitaxy has been used to grow microcrystalline clusters of gallium arsenide (GaAs) in the size range from 2.5 to 60 nanometers on high-purity, amorphous silica supports. High-resolution transmission electron microscopy reveals that clusters as small as 3.5 nanometers have good crystalline order with a lattice constant equal to that of bulk GaAs. Study of the microcrystallite surfaces by x-ray photoelectron spectroscopy shows that they are covered with a shell (1.0 to 1.5 nanometers thick) of native oxides of gallium and arsenic (Ga
2
O
3
and As
2
O
3
), whose presence could explain the low luminescence efficiency of the clusters. Optical absorption spectra of the supported GaAs are consistent with the blue-shifted band edge expected for semiconductor microcrystallites in the quantum size regime.
Lignin-Like Compounds and Sporopollen in
Coleochaete
, an Algal Model for Land Plant Ancestry
Authors: Delwiche Charles F. , Graham Linda E. , Thomson Norman
Published: October 2006

Unusual cell wall structure and resistance to microbial degradation led to an investigation of resistant biopolymers in
Coleochaete
(Chlorophyta, class Charophyceae), a green alga on the evolutionary lineage that led to land plants. In
Coleochaete
that are undergoing sexual reproduction, vegetative cell walls contain material similar to lignin, a substance generally thought absent from green algae, and the zygote wall includes sporopollenin. Knowledge of chemically resistant compounds in
Coleochaete
may facilitate interpretation of the fossil record. Placental transfer cells in
Coleochaete orbicularis
and in the hornwort
Anthoceros
survive acetolysis and contain lignin-like compounds, implying a close relation between these taxa.
Negative Differential Resistance on the Atomic Scale: Implications for Atomic Scale Devices
Authors: Lyo In-Whan , Avouris Phaedon
Published: October 2006

Negative differential resistance (NDR) is the essential property that allows fast switching in certain types of electronic devices. With scanning tunneling microscopy (STM) and scanning tunneling spectroscopy, it is shown that the current-voltage characteristics of a diode configuration consisting of an STM tip over specific sites of a boron-exposed silicon(111) surface exhibit NDR. These NDR-active sites are of atomic dimensions (∼1 nanometer). NDR in this case is the result of tunneling through localized, atomic-like states. Thus, desirable device characteristics can be obtained even on the atomic scale.
Dextran Sulfate Suppression of Viruses in the HIV Family: Inhibition of Virion Binding to CD4
+
Cells
Authors: Mitsuya Hiroaki , Looney David J. , Kuno Sachiko , Ueno Ryuji , Wong-Staal Flossie , Broder Samuel
Published: October 2006

The first step in the infection of human T lymphocytes by human immunodeficiency virus type 1 (HIV-1) is attachment to the target cell receptor, the CD4 antigen. This step may be vulnerable to attack by antibodies, chemicals, or small peptides. Dextran sulfate (molecular weight approximately 8000), which has been given to patients as an anticoagulant or antilipemic agent for more than two decades, was found to block the binding of virions to various target T lymphocytes, inhibit syncytia formation, and exert a potent inhibitory effect against HIV-1 in vitro at concentrations that may be clinically attainable in human beings. This drug also suppressed the replication of HIV-2 in vitro. These observations could have theoretical and clinical implications in the strategy to develop drugs against HIV types 1 and 2.
Highly Cooperative Opening of Calcium Channels by Inositol 1,4,5-Trisphosphate
Authors: Meyer Tobias , Holowka David , Stryer Lubert
Published: October 2006

The kinetics of calcium release by inositol 1,4,5-trisphosphate (IP
3
) in permeabilized rat basophilic leukemia cells were studied to obtain insight into the molecular mechanism of action of this intracellular messenger of the phosphoinositide cascade. Calcium release from intracellular storage sites was monitored with fura-2, a fluorescent indicator. The dependence of the rate of calcium release on the concentration of added IP
3
in the 4 to 40 n
M
range showed that channel opening requires the binding of at least three molecules of IP
3
. Channel opening occurred in the absence of added adenosine triphosphate, indicating that IP
3
acts directly on the channel or on a protein that gates it. The channels were opened by IP
3
in less than 4 seconds. The highly cooperative opening of calcium channels by nanomolar concentrations of IP
3
enables cells to detect and amplify very small changes in the concentration of this messenger in response to hormonal, sensory, and growth control stimuli.
Synthetic Amphiphilic Peptide Models for Protein Ion Channels
Authors: Lear J. D. , Wasserman Z. R. , DeGrado W. F.
Published: October 2006

Ion channel proteins are important for the conduction of ions across biological membranes. Recent analyses of their sequences have suggested that they are composed of bundles of α-helices that associate to form ion-conducting channels. To gain insight into the mechanisms by which α-helices can aggregate and conduct ions, three model peptides containing only leucine and serine residues were synthesized and characterized. A 21-residue peptide, H
2
N-(Leu-Ser-Ser-Leu-Leu-Ser-Leu)
3
-CONH
2
, which was designed to be a membrane-spanning amphiphilic α-helix, formed well-defined ion channels with ion permeability and lifetime characteristics resembling the acetylcholine receptor. In contrast, a 14-residue version of this peptide, which was too short to span the phospholipid bilayer as an α-helix, failed to form discrete, stable channels. A third peptide, H
2
N-(Leu-Ser-Leu-Leu-Leu-Ser-Leu)
3
-CONH
2
, in which one serine per heptad repeat was replaced by leucine, produced proton-selective channels. Computer graphics and energy minimization were used to create molecular models that were consistent with the observed properties of the channels.
The Gramicidin Pore: Crystal Structure of a Cesium Complex
Authors: Wallace B. A. , Ravikumar K.
Published: October 2006

Gramicidin, a linear polypeptide composed of hydrophobic amino acids with alternating L- and D- configurations, forms transmembrane ion channels. The crystal structure of a gramicidin-cesium complex has been determined at 2.0 angstrom resolution. In this structure, gramicidin forms a 26 angstrom long tube comprised of two polypeptide chains arranged as antiparallel beta strands that are wrapped into a left-handed helical coil with 6.4 residues per turn. The polypeptide backbone forms the interior of the hydrophilic, solvent-filled pore and the side chains form a hydrophobic and relatively regular surface on the outside of the pore. This example of a crystal structure of a solvent-filled ion pore provides a basis for understanding the physical nature of ion translocation.
Antisense RNA Directed Against the 3′ Noncoding Region Prevents Dormant mRNA Activation in Mouse Oocytes
Authors: Strickland Sidney , Huarte Joaquin , Belin Dominique , Vassalli Anne , Rickles Richard J. , Vassalli Jean-Dominique
Published: October 2006

Primary mouse oocytes contain untranslated stable messenger RNA for tissue plasminogen activator (t-PA). During meiotic maturation, this maternal mRNA undergoes a 3′-polyadenylation, is translated, and is degraded. Injections of maturing oocytes with different antisense RNA's complementary to both coding and noncoding portions of t-PA mRNA all selectively blocked t-PA synthesis. RNA blot analysis of t-PA mRNA in injected, matured oocytes suggested a cleavage of the RNA⋅RNA hybrid region, yielding a stable 5′ portion, and an unstable 3′ portion. In primary oocytes, the 3′ noncoding region was susceptible to cleavage, while the other portions of the mRNA were blocked from hybrid formation until maturation occurred. Injection of antisense RNA complementary to 103 nucleotides of its extreme 3′ untranslated region was sufficient to prevent the polyadenylation, translational activation, and destabilization of t-PA mRNA. These results demonstrate a critical role for the 3′ noncoding region of a dormant mRNA in its translational recruitment during meiotic maturation of mouse oocytes.
Effect of Neuropeptides on Production of Inflammatory Cytokines by Human Monocytes
Authors: Lotz Martin , Vaughan John H. , Carson Dennis A.
Published: October 2006

Two groups of mediators, the neuropeptides substance P and K and the monocyte-derived cytokines, interact in the neural regulation of immunological and inflammatory responses. Substance P, substance K, and the carboxyl-terminal peptide SP(4-11) induce the release of interleukin-1, tumor necrosis factor-α, and interleukin-6 from human blood monocytes. The neuropeptide effects occur at low doses, are specific as shown by inhibition studies with a substance P antagonist, and require de novo protein synthesis. Since monocyte-derived cytokines regulate multiple cellular functions in inflammation and immunity and since neuropeptides can be released from peripheral nerve endings into surrounding tissues, these findings identify a potent mechanism for nervous system regulation of host defense responses.
Site-Directed Neovessel Formation in Vivo
Authors: Thompson John A. , Anderson Kathryn D. , DiPietro Judith M. , Zwiebel James A. , Zametta Massimo , Anderson W. French , Maciag Thomas
Published: October 2006

Angiogenesis is an important component of organogenesis and wound repair and occurs during the pathology of oncogenesis, atherogenesis, and other disease processes. Thus, it is important to understand the physiological mechanisms that control neovascularization, especially with methods that permit the molecular dissection of the phenomenon in vivo. Heparin-binding growth factor-1 was shown to bind to collagen type I and type IV. When complexed with gelatin, heparin-binding growth factor-1 can induce neovascularization at polypeptide concentrations that are consistent with the biological activity of the mitogen in vitro. The adsorption strategy induces rapid blood vessel formation at and between organ- and tissue-specific sites and permits recovery of the site-specific implant for examination and manipulation by molecular methods.
Ryanodine Receptor of Skeletal Muscle Is a Gap Junction-Type Channel
Authors: Ma Jianjie , Fill Michael , Knudson C. Michael , Campbell Kevin P. , Coronado Roberto
Published: October 2006

In the sarcoplasmic reticulum membrane of skeletal muscle, the ryanodine receptor forms an aqueous pore identified as the calcium-release pathway that operates during excitation-contraction coupling. The purified ryanodine receptor channel has now been shown to have four properties usually associated with gap junction channels: (i) a large nonspecific voltage-dependent conductance consisting of several open states; (ii) an inhibition of open probability by low
p
H; (iii) an inhibition of open probability by calcium; and (iv) a sensitivity to blockade by heptanol and octanol but not other alcohols. This functional homology may provide an insight into the mechanism of how muscle cells transduce depolarization into an intracellular release of calcium.
Angiogenic Properties of Kaposi's Sarcoma-Derived Cells After Long-Term Culture in Vitro
Authors: Salahuddin S. Zaki , Nakamura Shuji , Biberfeld Peter , Kaplan Mark H. , Markham Phillip D. , Larsson Lena , Gallo Robert C.
Published: October 2006

Cells derived from lung biopsies and pleural effusions from AIDS patients with Kaposi's sarcoma (KS) of the lungs were established in long-term culture with the aid of conditioned medium from HTLV-II-transformed T cells (HTLV-II CM). These AIDS-KS cells were similar to the so-called spindle cells in KS lesions and had some of their features. They produced factors that supported their own growth (autocrine) and the growth of other cells (paracrine), including umbilical vein endothelium and fibroblasts. That the AIDS-KS cells also expressed potent angiogenic activity was demonstrated by the chorioallantoic membrane assay and by subcutaneous inoculation of AIDS-KS cells into nude mice, which resulted in the development of angiogenic lesions composed of mouse cells and showing histological features similar to those of human KS lesions. These data suggest that AIDS-associated KS and possibly other types of KS may be initiated by signals that induce the growth of particular cells (spindle cells of lymphatic or vascular origin) and the expression of autocrine and paracrine activities.
Systems Analysis at the Molecular Scale
Authors: Rabitz Herschel
Published: October 2006

Problems involving physiochemical phenomena on both the microscopic and macroscopic scales often raise similar sets of generic issues and questions. The complexity of these problems is beginning to make inoperative the traditional intuition-based approaches to their analysis and solution. The common characteristics of large, multivariable, complex molecular systems call for a new, more systematic approach to guide theoretical and experimental efforts. With mathematical modeling becoming an essential ingredient in the studies, it is argued that molecular systems analysis and especially the systematic tools of sensitivity analysis can play an increasingly important role in understanding and finding solutions to complex, chemically based problems.
A Devonian Spinneret: Early Evidence of Spiders and Silk Use
Authors: Shear William A. , Palmer Jacqueline M. , Coddington Jonathan A. , Bonamo Patricia M.
Published: October 2006

A nearly complete spider spinneret was found in Middle Devonian rocks (about 385 to 380 million years old) near Gilboa, New York. This is the earliest evidence yet discovered for silk production from opisthosomal spigots, and therefore for spiders. Two previously known Devonian fossils described as spiders lack any apomorphies of the order Araneae and are probably not spiders. The spigots of the Devonian spinneret resemble those of members of the living suborder Mesothelae, but the number of spigots and their distribution are like those of members of the suborder Opisthothelae, infraorder Mygalomorphae. The Devonian spider belonged to a clade that may be the sister group of all other spiders, of Mesothelae, or of Opisthothelae.
Preparation of Organometallic Compounds from Highly Reactive Metal Powders
Authors: Rieke Reuben D.
Published: October 2006

The formation of novel organometallic compounds by the reaction of organic substrates with finely divided metal powders represents a powerful tool for the synthetic chemist. The direct reaction with a zerovalent metal is the only viable method of synthesis for many of these compounds. Accordingly, chemists have been actively developing new methods for increasing the reactivity of metal powders toward organic substrates. Three principal approaches have been developed in recent years: the metal vaporization method, sonochemistry, and the preparation of finely divided metal powders by the reduction of metal salts. A number of new methods of synthesis have resulted from these studies.
Origins of Agriculture in Eastern North America
Authors: Smith Bruce D.
Published: October 2006

As a result of research carried out over the past decade, eastern North America now provides one of the most detailed records of the origins of agriculture available. Spanning a full three millennia, the transition from forager to farmer in eastern North America involved the domestication of four North American seed plants during the second millennium B.C., the initial emergence of food production economies based on local crop plants between 250 B.C. and A.D. 200, and the rapid and broad-scale shift to maize-centered agriculture during the three centuries from A.D. 800 to 1100.
A cAMP-Regulated Chloride Channel in Lymphocytes That Is Affected in Cystic Fibrosis
Authors: Chen Jennifer H. , Schulman Howard , Gardner Phyllis
Published: October 2006

A defect in regulation of a chloride channel appears to be the molecular basis for cystic fibrosis (CF), a common lethal genetic disease. It is shown here that a chloride channel with kinetic and regulatory properties similar to those described for secretory epithelial cells is present in both T and B lymphocyte cell lines. The regulation of the channels by adenosine 3′,5′-monophosphate (cAMP)-dependent protein kinase in transformed B cells from CF patients is defective. Thus, lymphocytes may be an accessible source of CF tissue for study of this defect, for cloning of the chloride channel complex, and for diagnosis of the disease.
Role of Phosphatidylinositol Kinase in PDGF Receptor Signal Transduction
Authors: Coughlin Shaun R. , Escobedo Jaime A. , Williams Lewis T.
Published: October 2006

The molecules with which the platelet-derived growth factor (PDGF) receptor interacts to elicit the biochemical reactions responsible for cell proliferation have not been identified. Antisera directed against specific PDGF receptor peptides coprecipitated a phosphatidylinositol (PI) kinase and the PDGF receptor. Immunoprecipitates from PDGF-stimulated cells contained 10 to 50 times as much PI kinase as those from unstimulated cells. Mutation of the PDGF receptor by deletion of its kinase insert region resulted in a receptor markedly less effective than the wild type in eliciting cell proliferation and defective in PDGF-stimulated PI kinase, but still capable of PDGF-induced receptor autophosphorylation and phosphoinositide hydrolysis. These data show that the PDGF receptor is physically associated with a PDGF-sensitive PI kinase that is distinct from tyrosine kinase and is not required for PDGF-induced PI hydrolysis. The finding that the mutant PDGF receptor missing the kinase insert domain elicited known early biochemical responses to PDGF, but did not associate with or regulate PI kinase, suggests a novel role for the receptor-associated PI kinase in the transmission of mitogenic signals.
Ceramic Thin Films: Fabrication and Applications
Authors: Sayer M. , Sreenivas K.
Published: October 2006

Ceramics are a distinct class of materials whose properties range from extreme hardness to unique electrical behavior. New methods of creating thin films of complex oxides and electronic ceramics allow the integration of these properties with semiconductor technology and raise the possibility of a new range of electronic devices.
Venus: A Contrast in Evolution to Earth
Authors: Kaula William M.
Published: October 2006

Of the planets, Venus and Earth are by far the most similar in primary properties, yet they differ markedly in secondary properties. A great impact into Earth is believed to have created its moon and removed its atmosphere; the lack of such an impact into Venus apparently led to a greatly differing atmospheric evolution. The lack of an ocean on Venus prevents the recycling of volatiles and inhibits subduction, so that its crust is probably more voluminous than Earth's, although distorted and quite variable in thickness. Venus's upper mantle appears to be depleted in both volatiles and energy sources because, in addition to the lack of volatile recycling, melts of mantle rocks are more dense than their solid matrix at pressures above 8 gigapascals and hence sink if they occur at depths below 250 kilometers. Appreciable energy sources persist at great depths to sustain the few great mountain complexes. The greatest current problem is reconciling the likelihood of a voluminous crust with indications of considerable strength at shallow depths of 20 to 100 kilometers.
Deep Magma Body Beneath the Summit and Rift Zones of Kilauea Volcano, Hawaii
Authors: Delaney Paul T. , Fiske Richard S. , Miklius Asta , Okamura Arnold T. , Sako Maurice K.
Published: October 2006

A magnitude 7.2 earthquake in 1975 caused the south flank of Kilauea Volcano, Hawaii, to move seaward in response to slippage along a deep fault. Since then, a large part of the volcano's edifice has been adjusting to this perturbation. The summit of Kilauea extended at a rate of 0.26 meter per year until 1983, the south flank uplifted more than 0.5 meter, and the axes of both the volcano's rift zones extended and subsided; the summit continues to subside. These ground-surface motions have been remarkably steady and much more widespread than those caused by either recurrent inflation and deflation of the summit magma chamber or the episodic propagation of dikes into the rift zones. Kilauea's magmatic system is, therefore, probably deeper and more extensive than previously thought; the summit and both rift zones may be underlain by a thick, near vertical dike-like magma system at a depth of 3 to 9 kilometers.
Stereochemical Course of Catalysis by the
Tetrahymena
Ribozyme
Authors: Rajagopal Jayaraj , Doudna Jennifer A. , Szostak Jack W.
Published: October 2006

The group I intron from
Tetrahymena
catalyzes phosphodiester transfer reactions on various RNA substrates. A modified RNA substrate with a phosphorothioate group in one stereoisomeric form at the site of reaction was synthesized in order to determine the stereochemical course of an RNA-catalyzed reaction. The reaction product was digested with a stereospecific nuclease to determine the configuration of the product phosphorothioate. The reaction occurs with inversion of configuration at phosphorus, implying an in-line pathway for the reaction.
Regulation of Chloride Channels by Protein Kinase C in Normal and Cystic Fibrosis Airway Epithelia
Authors: Li Ming , McCann John D. , Anderson Matthew P. , Clancy John P. , Liedtke Carole M. , Nairn Angus C. , Greengard Paul , Welsch Michael J.
Published: October 2006

Apical membrane chloride channels control chloride secretion by airway epithelial cells. Defective regulation of these channels is a prominent characteristic of cystic fibrosis. In normal intact cells, activation of protein kinase C (PKC) by phorbol ester either stimulated or inhibited chloride secretion, depending on the physiological status of the cell. In cell-free membrane patches, PKC also had a dual effect: at a high calcium concentration, PKC inactivated chloride channels; at a low calcium concentration, PKC activated chloride channels. In cystic fibrosis cells, PKC-dependent channel inactivation was normal, but activation was defective. Thus it appears that PKC phosphorylates and regulates two different sites on the channel or on an associated membrane protein, one of which is defective in cystic fibrosis.
Activation of Apical Chloride Channels in the Gastric Oxyntic Cell
Authors: Demarest Jeffery R. , Loo Donald D. F. , Sachs George
Published: October 2006

Oxyntic cells that retain distinct morphological polarity between apical and basolateral membranes were isolated from the gastric mucosa of the amphibian
Necturus
. Patch-clamp techniques were applied to these cells to identify apical membrane ion channels associated with hydrochloric acid secretion. A single class of voltage-dependent, inwardly rectifying chloride channels was observed in the apical membranes of both resting and stimulated (acid-secreting) oxyntic cells. Stimulation of the cells with dibutyryladenosine 3′,5′-monophosphate and isobutylmethylxanthine increased channel open probability and simultaneously increased apical membrane surface area. This chloride channel is probably responsible for electrogenic chloride secretion by the gastric mucosa and may also participate in the fluid- and enzyme-secretory functions of the oxyntic cell, analogous to the chloride channels found in the apical membranes of other exocrine cells.
Neurotoxicity of a Fragment of the Amyloid Precursor Associated with Alzheimer's Disease
Authors: Yankner Bruce A. , Dawes Linda R. , Fisher Shannon , Villa-Komaroff Lydia , Oster-Granite Mary Lou , Neve Rachael L.
Published: October 2006

Amyloid deposition in senile plaques and the cerebral vasculature is a marker of Alzheimer's disease. Whether amyloid itself contributes to the neurodegenerative process or is simply a by-product of that process is unknown. Pheochromocytoma (PC12) and fibroblast (NIH 3T3) cell lines were transfected with portions of the gene for the human amyloid precursor protein. Stable PC12 cell transfectants expressing a specific amyloid-containing fragment of the precursor protein gradually degenerated when induced to differentiate into neuronal cells with nerve growth factor. Conditioned medium from these cells was toxic to neurons in primary hippocampal cultures, and the toxic agent could be removed by immunoabsorption with an antibody directed against the amyloid polypeptide. Thus, a peptide derived from the amyloid precursor may be neurotoxic.
Isolation of Human Transcribed Sequences from Human-Rodent Somatic Cell Hybrids
Authors: Liu Pu , Legerski Randy , Siciliano Michael J.
Published: October 2006

A method was developed for selectively isolating genes from localized regions of the human genome that are contained in interspecific hybrid cells. Complementary human DNA was prepared from a human-rodent somatic cell hybrid that contained less than 1% human DNA, by using consensus 5′ intron splice sequences as primers. These primers would select immature, unspliced messenger RNA (still retaining species-specific repeat sequences) as templates. Screening a derived complementary DNA library for human repeat sequences resulted in the isolation of human clones at the anticipated frequency with characteristics expected of exons of transcribed human genes—single copy sequences that hybridized to discrete bands on Northern (RNA) blots.
Vaccination with a Synthetic Zona Pellucida Peptide Produces Long-Term Contraception in Female Mice
Authors: Millar Sarah E. , Chamow Steven M. , Baur Anne W. , Oliver Constance , Robey Frank , Dean Jurrien
Published: October 2006

The zona pellucida surrounding mouse oocytes is an extracellular matrix composed of three sulfated glycoproteins, ZP1, ZP2, and ZP3. It has been demonstrated that a monoclonal antibody to ZP3 injected into female mice inhibits fertilization by binding to the zona pellucida and blocking sperm penetration. A complementary DNA encoding ZP3 was randomly cleaved and 200- to 1000-base pair fragments were cloned into the expression vector λgt11. This epitope library was screened with the aforementioned contraceptive antibody, and the positive clones were used to map the seven-amino acid epitope recognized by the antibody. Female mice were immunized with a synthetic peptide containing this B cell epitope coupled to a carrier protein to provide helper T cell epitopes. The resultant circulating antibodies to ZP3 bound to the zona pellucida of immunized animals and produced long-lasting contraception. The lack of ovarian histopathology or cellular cytotoxicity among the immunized animals may be because of the absence of zona pellucida T cell epitopes in this vaccine.
Supply and Demand for Scientists and Engineers: A National Crisis in the Making
Authors: Atkinson Richard C.
Published: October 2006

Projections are analyzed for the future supply and demand of scientists and engineers. The demographics of the college-age population combined with estimates of the percentage of students who will pursue careers in science and engineering indicate significant shortfalls between supply and demand for the next several decades at both the baccalaureate and Ph.D. levels. If these projections are realized, the shortage of technical personnel will have a major impact on economic growth, international competitiveness, and national security. Various strategies for recruiting and retaining students in science and engineering are considered.
Atomistic Mechanisms and Dynamics of Adhesion, Nanoindentation, and Fracture
Authors: Landman Uzi , Luedtke W. D. , Burnham Nancy A. , Colton Richard J.
Published: October 2006

Molecular dynamics simulations and atomic force microscopy are used to investigate the atomistic mechanisms of adhesion, contact formation, nanoindentation, separation, and fracture that occur when a nickel tip interacts with a gold surface. The theoretically predicted and experimentally measured hysteresis in the force versus tip-to-sample distance relationship, found upon approach and subsequent separation of the tip from the sample, is related to inelastic deformation of the sample surface characterized by adhesion of gold atoms to the nickel tip and formation of a connective neck of atoms. At small tip-sample distances, mechanical instability causes the tip and surface to jump-to-contact, which in turn leads to adhesion-induced wetting of the nickel tip by gold atoms. Subsequent indentation of the substrate results in the onset of plastic deformation of the gold surface. The atomic-scale mechanisms underlying the formation and elongation of a connective neck, which forms upon separation, consist of structural transformations involving elastic and yielding stages.
Upper Eocene Gilled Mushroom from the Dominican Republic
Authors: Poinar George O. , Singer Rolf
Published: October 2006

Coprinites dominicana
gen.nov., spec.nov. (Coprinaceae) found in amber from the Dominican Republic is the earliest known gilled mushroom, the first fossil fleshy agaric determinable, and the only known fossil "mushroom" (Agaricales) from the tropics. This find is of significance with respect to the evolutionary development of the Basidiomycetes. Because the appearance of this fossil is quite modern, it suggests that mushrooms as a group probably arose much earlier than the early to mid-Tertiary.
Axial Oxygen-Centered Lattice Instabilities and High-Temperature Superconductivity
Authors: Conradson Steven D. , Raistrick Ian D. , Bishop Alan R.
Published: October 2006

Copper K-edge x-ray absorption data indicate that an axial oxygen-centered lattice instability accompanying the 93 K superconducting transition in YBa
2
Cu
3
O
7
is of a pseudo-(anti)ferroelectric type, in that it appears to involve the softening of a double potential well into a structure in which the difference between the two copper-oxygen distances and the barrier height have both decreased. This softer structure is present only at temperatures within a fluctuation region around the transition. A similar process involving the analogous axial oxygen atom also accompanies the superconducting transition in TlBa
2
Ca
3
Cu
4
O
11
, where the superconducting transition temperature
T
c
is ∼120 K. The mean square relative displacement of this oxygen atom in YBa
2
Cu
3
O
7
is also specifically affected by a reduction in the oxygen content and by the substitution of cobalt for copper, providing further evidence for the sensitivity of the displacement to additional factors that also influence the superconductivity. On the basis of the implied coupling of this ionic motion to the superconductivity, a scenario for high-temperature superconductivity is presented in which both phonon and electronic (charge transfer) channels are synergistically involved.
RNA Editing in Plant Mitochondria
Authors: Hiesel Rudolf , Wissinger Bernd , Schuster Wolfgang , Brennicke Axel
Published: October 2006

Comparative sequence analysis of genomic and complementary DNA clones from several mitochondrial genes in the higher plant
Oenothera
revealed nucleotide sequence divergences between the genomic and the messenger RNA-derived sequences. These sequence alterations could be most easily explained by specific post-transcriptional nucleotide modifications. Most of the nucleotide exchanges in coding regions lead to altered codons in the mRNA that specify amino acids better conserved in evolution than those encoded by the genomic DNA. Several instances show that the genomic arginine codon CGG is edited in the mRNA to the tryptophan codon TGG in amino acid positions that are highly conserved as tryptophan in the homologous proteins of other species. This editing suggests that the standard genetic code is used in plant mitochondria and resolves the frequent coincidence of CGG codons and tryptophan in different plant species. The apparently frequent and non-species-specific equivalency of CGG and TGG codons in particular suggests that RNA editing is a common feature of all higher plant mitochondria.
A Molecular Ferromagnet with a Curie Temperature of 6.2 Kelvin: [Mn(C
5
(CH
3
)
5
)
2
]
+
[TCNQ]
-
Authors: Broderick W. E. , Thompson J. A. , Day E. P. , Hoffman B. M.
Published: October 2006

The study of magnetic phase transitions in insulating molecular solids provides new insights into mechanisms of magnetic coupling in the solid state and into critical phenomena associated with these transitions. Only a few such materials are known to display cooperative magnetic properties. The use of high-spin molecular components would enhance intermolecular spin-spin interactions and thus a series of charge-transfer (CT) salts have been synthesized that utilize the spin
S
= 1 molecular cation, [Mn(C
5
(CH
3
)
5
)
2
]
+
(decamethylmanganocenium). The structure and cooperative magnetic behavior of [Mn(C
5
(CH
3
)
5
)
2
]
+
[TCNQ]
-
(decamethylmanganocenium 7,7,8,8-tetracyano-
p
-quinodimethanide) are reported. This salt is a bulk molecular ferromagnet with the highest critical (Curie) temperature (
T
c
= 6.2 K) and coercive field (3.6 × 10
3
gauss), yet reported for such a material.
From Force Fields to Dynamics: Classical and Quantal Paths
Authors: Truhlar Donald G. , Gordon Mark S.
Published: October 2006

Reaction path methods provide a powerful tool for bridging the gap between electronic structure and chemical dynamics. Classical mechanical reaction paths may usually be understood in terms of the force field in the vicinity of a minimum energy path (MEP). When there is a significant component of hydrogenic motion along the MEP and a barrier much higher than the average energy of reactants, quantal tunneling paths must be considered, and these tend to be located on the corner-cutting side of the MEP. As the curvature of the MEP in mass-scaled coordinates is increased, the quantal reaction paths may deviate considerably from the classical ones, and the force field must be mapped out over a wider region, called the reaction swath. The required force fields may be represented by global or semiglobal analytic functions, or the dynamics may be computed "directly" from the electronic structure results without the intermediacy of potential energy functions. Applications to atom and diatom reactions in the gas phase and at gas-solid interfaces and to reactions of polyatomic molecules in the gas phase, in clusters, and in aqueous solution are discussed as examples.
Seismic Trapped Modes in the Oroville and San Andreas Fault Zones
Authors: Li Yong-Gang , Leary Peter , Aki Keiiti , Malin Peter
Published: October 2006

Three-component borehole seismic profiling of the recently active Oroville, California, normal fault and microearthquake event recording with a near-fault three-component borehole seismometer on the San Andreas fault at Parkfield, California, have shown numerous instances of pronounced dispersive wave trains following the shear wave arrivals. These wave trains are interpreted as fault zone-trapped seismic modes. Parkfield earthquakes exciting trapped modes have been located as deep as 10 kilometers, as shallow as 4 kilometers, and extend 12 kilometers along the fault on either side of the recording station. Selected Oroville and Parkfield wave forms are modeled as the fundamental and first higher trapped SH modes of a narrow low-velocity layer at the fault. Modeling results suggest that the Oroville fault zone is 18 meters wide at depth and has a shear wave velocity of 1 kilometer per second, whereas at Parkfield, the fault gouge is 100 to 150 meters wide and has a shear wave velocity of 1.1 to 1.8 kilometers per second. These low-velocity layers are probably the rupture planes on which earthquakes occur.
Negative Pressure-Temperature Slopes for Reactions Formign MgSiO
3
Perovskite from Calorimetry
Authors: Ito E. , Akaogi M. , Topor L. , Navrotsky A.
Published: October 2006

A new and sensitive differential drop solution calorimetric technique was developed for very small samples. A single experiment using one 5.18-milligram sample of perovskite, synthesized at 25 gigapascals and 1873 Kelvin, gave 110.1 ± 4.1 kilojoules per mole for the enthalpy of the ilmenite-perovskite transition in MgSiO
3
. The thermodynamics of the reaction of MgSiO
3
(ilmenite) to MgSiO
3
(perovskite) and of Mg
2
SiO
4
(spinel) to MgSiO
3
(perovskite) and MgO (periclase) were assessed. Despite uncertainties in heat capacity and molar volume at high pressure and temperature, both reactions clearly have negative pressure-temperature slopes, -0.005 ± 0.002 and -0.004 ± 0.002 gigapascals per Kelvin, respectively. The latter may be insufficiently negative to preclude whole-mantle convection.
Innovative Approaches to Plasminogen Activator Therapy
Authors: Haber Edgar , Quertermous Thomas , Matsueda Gary R. , Runge Marschall S.
Published: October 2006

Plasminogen activator therapy for acute myocardial infarction has become standard medical practice. Bleeding complications, however, limit the utility of the currently available agents. This article reviews how the tools of molecular biology and protein engineering are being used to develop safer and more effective plasminogen activators.
Female Preference Predates the Evolution of the Sword in Swordtail Fish
Authors: Basolo Alexandra L.
Published: October 2006

The study of female preferences and the evolution of male traits has until recently centered on genetic coevolutionary mechanisms. An alternative mechanism posits that a preference results from a preestablished bias in the female information-processing system arising from sources independent of sexual selection. Male traits then arise that are selected by this preexisting preference. The genus
Xiphophorus
consists of swordless platyfish and swordtails. Swordlessness is the primitive state. In this study, female platyfish,
X. maculatus
, were found to prefer conspecific males with artificial swords over those without swords, despite evidence that the common ancestor of platyfish and swordtails was swordless. These results suggest that the evolution of the sword in the swordtail clade was a consequence of selection arising from a preexisting bias.
Effects of Fish in River Food Webs
Authors: Power Mary E.
Published: October 2006

Experimental manipulations of fish in a Northern California river during summer base flow reveal that they have large effects on predators, herbivores, and plants in river food webs. California roach and juvenile steelhead consume predatory insects and fish fry, which feed on algivorous chironomid larvae. In the presence of fish, filamentous green algae are reduced to low, prostrate webs, infested with chironomids. When the absence of large fish releases smaller predators that suppress chironomids, algal biomass is higher, and tall upright algal turfs become covered with diatoms and cyanobacteria. These manipulations provide evidence that the Hairston, Smith, Slobodkin–Fretwell theory of trophic control, which predicts that plants will be alternately limited by resources or herbivores in food webs with odd and even numbers of trophic levels, has application to river communitics.
Modern Cyanobacterial Analogs of Paleozoic Stromatoporoids
Authors: Kaźmierczak Józef , Kempe Stephan
Published: October 2006

Recent and subfossil calcareous structures resembling cystose and subclathrate Paleozoic stromatoporoids have been discovered in a sea-linked, stratified, alkaline crater lake on Satonda Island, Indonesia. The structures are produced by mats of coccoid cyanobacteria growing along the lakeshore from the water surface down to the O2-H2S interface located at a depth of 22.8 meters. Calcification of the mats is controlled by seasonal changes in calcium carbonate supersaturation in the epilimnion. The internally complex structures are a product of two different calcification processes: (i) periodic in vivo calcification of the surficial cyanobacterial layers by low-Mg calcite, and (ii) early postmortem calcification of the cyanobacterial aggregates below the mat surface by microbially precipitated aragonite. The finding supports the idea that Paleozoic stromatoporoids represent fossilized cyanobacteria (stromatolites). It also implies that the stromatoporoid-generating epicontinental seas during the early Paleozoic may have been more alkaline and had a higher carbonate mineral supersaturation than modern seawater.
Biomass Burning in the Tropics: Impact on Atmospheric Chemistry and Biogeochemical Cycles
Authors: Crutzen Paul J. , Andreae Meinrat O.
Published: October 2006

Biomass burning is widespread, especially in the tropics. It serves to clear land for shifting cultivation, to convert forests to agricultural and pastoral lands, and to remove dry vegetation in order to promote agricultural productivity and the growth of higher yield grasses. Furthermore, much agricultural waste and fuel wood is being combusted, particularly in developing countries. Biomass containing 2 to 5 petagrams of carbon is burned annually (1 petagram = 1015grams), producing large amounts of trace gases and aerosol particles that play important roles in atmospheric chemistry and climate. Emissions of carbon monoxide and methane by biomass burning affect the oxidation efficiency of the atmosphere by reacting with hydroxyl radicals, and emissions of nitric oxide and hydrocarbons lead to high ozone concentrations in the tropics during the dry season. Large quantities of smoke particles are produced as well, and these can serve as cloud condensation nuclei. These particles may thus substantially influence cloud microphysical and optical properties, an effect that could have repercussions for the radiation budget and the hydrological cycle in the tropics. Widespread burning may also disturb biogeochemical cycles, especially that of nitrogen. About 50 percent of the nitrogen in the biomass fuel can be released as molecular nitrogen. This pyrodenitrification process causes a sizable loss of fixed nitrogen in tropical ecosystems, in the range of 10 to 20 teragrams per year (1 teragram = 1012grams).
Defining the Inside and Outside of a Catalytic RNA Molecule
Authors: Latham John A. , Cech Thomas R.
Published: October 2006

Ribozymes are RNA molecules that catalyze biochemical reactions. Fe(II)-EDTA, a solvent-based reagent which cleaves both double- and single-stranded RNA, was used to investigate the structure of the
Tetrahymena
ribozyme. Regions of cleavage alternate with regions of substantial protection along the entire RNA molecule. In particular, most of the catalytic core shows greatly reduced cleavage. These data constitute experimental evidence that an RNA enzyme, like a protein enzyme, has an interior and an exterior. Determination of positions where the phosphodiester backbone of the RNA is on the inside or on the outside of the molecule provides major constraints for modeling the three-dimensional structure of the
Tetrahymena
ribozyme. This approach should be generally informative for structured RNA molecules.
Subsistence Economy of El Paraíso, an Early Peruvian Site
Authors: Quilter Jeffrey , Ojeda E. Bernardino , Pearsall Deborah M. , Sandweiss Daniel H. , Jones John G. , Wing Elizabeth S.
Published: October 2006

Studies of food remains from the Preceramic monumental site of El Paraíso, Peru (1800 to 1500 B.C.), have shed new light on a debate regarding the relative importance of seafood versus terrestrial resources and the role of cultigens in subsistence economies during the early development of Peruvian civilization. Fish was the primary animal food at the site whereas plant foods consisted of a mixture of cultivated resources (squashes, beans, peppers, and
jicama
) with an additional reliance on fruits (guava,
lucuma
, and
pacae
). Wild plants, especially the roots of sedges and cat-tail, also may have accounted for a substantial part of the diet. Cotton was a chief crop, used in making fishing tackle and the textiles that served as clothing and items of high value and status. As an example of the beginnings of civilization, El Paraíso is a case in which impressive architecture was built on a relatively simple subsistence economy and energy was expended in the production of resources useful in local and regional exchange systems.
An Interplanetary Dust Particle Linked Directly to Type CM Meteorites and an Asteroidal Origin
Authors: Bradley J. P. , Brownlee D. E.
Published: October 2006

Tochilinite, an ordered mixed-layer mineral containing Mg, Al, Fe, Ni, S, and O, has been identified in an interplanetary dust particle (IDP). This mineral is found in only one other class of meteoritic materials, type CM carbonaceous chondrites. The presence of tochilinite in an IDP provides a direct petrogenetic link between a member of the layer-silicate subset of IDPs and a specific class of meteorites and thus establishes that some IDPs collected in the stratosphere have an asteroidal origin. The scarcity of this IDP type suggests that materials with CM mineralogy are not abundant among the dust-producing asteroids.
Modeling of Turing Structures in the Chlorite—Iodide—Malonic Acid—Starch Reaction System
Authors: Lengyel István , Epstein Irving R.
Published: October 2006

Recent experiments on the chlorite-iodide-malonic acid-starch reaction in a gel reactor give the first evidence of the existence of the symmetry breaking, reaction-diffusion structures predicted by Turing in 1952. A five-variable model that describes the temporal behavior of the system is reduced to a two-variable model, and its spatial behavior is analyzed. Structures have been found with wavelengths that are in good agreement with those observed experimentally. The gel plays a key role by binding key iodine species, thereby creating the necessary difference in the effective diffusion coefficients of the activator and inhibitor species, iodide and chlorite ions, respectively.