bluuebunny/crossref_metadata_2025 huggingface dataset:
Preceramic Occupations in the Orinoco River Valley
Authors: Barse William P.
Published: October 2006

Two sites in the Orinoco Valley containing preceramic remains from excavated contexts are described. Radiocarbon dating and stylistic comparisons indicate that the northern tropical lowlands were inhabited at the onset of the Holocene, suggesting a time depth of 9000 years before the present for tropical forest-savanna adaptations in northern South America.
Oxygen Isotope Effect and Structural Phase Transitions in La
2
CuO
4
-Based Superconductors
Authors: Crawford M. K. , Farneth W. E. , McCarron E. M. , Harlow R. L. , Moudden A. H.
Published: October 2006

The oxygen isotope effect on the superconducting transition temperature (α
o
) varies as a function of
x
in La

2-
x

Sr

x

CuO
4
and La

2-
x

Ba

x

CuO
4
, with the maximum α
o
values (α
o
≥ 0.5) found for
x
near 0.12. This unusual
x
dependence implies that the isotope effect is influenced by proximity to the
Abma
→

P4
2
/ncm

structural phase transition in these systems. Synchrotron x-ray diffraction measurements reveal little change in lattice parameters or orthorhombicity due to isotope exchange in strontium-doped materials where α
o
> 0.5, eliminating static structural distortion as a cause of the large isotope effects. The anomalous behavior of α
o
in both strontium- and barium-doped materials, in combination with the previously discovered
Abma
→

P4
2
/ncm

structural phase-transition in La
1.88
Ba
0.12
CuO
4
, suggests that an electronic contribution to the lattice instability is present and maximizes at ∼1/8 hole per copper atom. These observations indicate a close connection between hole doping of the Cu-O sheets, tilting instabilities of the CuO
6
octahedra, and superconductivity in La
2
CuO
4
-based superconductors.
Targeting of Nonexpressed Genes in Embryonic Stem Cells Via Homologous Recombination
Authors: Johnson Randall S. , Sheng Morgan , Greenberg Michael E. , Kolodner Richard D. , Papaioannou Virginia E. , Spiegelman Bruce M.
Published: October 2006

Gene targeting via homologous recombination-mediated disruption in murine embryonic stem (ES) cells has been described for a number of different genes expressed in these cells; it has not been reported for any nonexpressed genes. Pluripotent stem cell lines were isolated with homologously recombined insertions at three different loci: c-
fos
, which is expressed at a low level in ES cells, and two genes, adipsin and adipocyte P2 (aP2), which are transcribed specifically in adipose cells and are not expressed at detectable levels in ES cells. The frequencies at which homologous recombination events occurred did not correlate with levels of expression of the targeted genes, but did occur at rates comparable to those previously reported for genes that are actively expressed in ES cells. Injection of successfully targeted cells into mouse blastocysts resulted in the formation of chimeric mice. These studies demonstrate the feasibility of altering genes in ES cells that are expressed in a tissue-specific manner in the mouse, in order to study their function at later developmental stages.
Approaches for Optimizing the First Electronic Hyperpolarizability of Conjugated Organic Molecules
Authors: Marder S. R. , Beratan D. N. , Cheng L.-T.
Published: October 2006

A two-state, four-orbital, independent electron analysis of the first optical molecular hyperpolarizability, β, leads to the prediction that |β| maximizes at a combination of donor and acceptor strengths for a given conjugated bridge. Molecular design strategies that focus on the energetic manipulations of the bridge states are proposed for the optimization of β. The limitations of molecular classes based on common bridge structures are highlighted and more promising candidates are described. Experimental results supporting the validity of this approach are presented.
Crystal Structure of Osmylated C
60
: Confirmation of the Soccer Ball Framework
Authors: Hawkins Joel M. , Meyer Axel , Lewis Timothy A. , Loren Stefan , Hollander Frederick J.
Published: October 2006

An x-ray crystal structure that confirms the soccer ball-shaped carbon framework of C
60
(buckminsterfullerene) is reported. An osmyl unit was added to C
60
in order to break its pseudospherical symmetry and give an ordered crystal. The crystal structure of this derivative, C
60
(OsO
4
)(4-
tert
-butylpyridine)
2
, reveals atomic positions within the carbon cluster.
Environmental Patterns in the Origins of Higher Taxa: The Post-Paleozoic Fossil Record
Authors: Jablonski David , Bottjer David J.
Published: October 2006

Of the 26 well-preserved orders of benthic marine invertebrates that have originated since the beginning of the Mesozoic, 20 first appear in onshore environments. This distribution differs significantly from that shown by well-preserved genera and families, and by the 16 poorly preserved orders. These discordances suggest that the pattern of preferential onshore origination is not an artifact of preservation or collection and that the origin of higher taxa cannot be regarded as a simple extrapolation of rates and patterns at lower levels. The onshore environment fosters production or enhances survivorship of species that initiate lineages tending to accumulate suites of derived characters and that thus are ultimately afforded high taxonomic rank.
Celestial Mechanics on a Microscopic Scale
Authors: Uzer T. , Farrelly David , Milligan John A. , Raines Paul. E. , Skelton Joel P.
Published: October 2006

Classical and semiclassical methods are unrivaled in providing an intuitive and computationally tractable approach to the study of atomic, molecular, and nuclear dynamics. An important advantage of such methods is their ability to uncover in a single picture underlying structures that may be hard to extract from the profusion of data supplied by detailed quantum calculations. Modern trends in semiclassical mechanics are described, particularly the combination of group theoretical methods with techniques of nonlinear dynamics. Application is made to intramolecular energy transfer and to the electronic structure of atomic Rydberg states in external electric and magnetic fields.
Numerical Models of Extragalactic Radio Sources
Authors: Burns Jack O. , Norman Michael L. , Clarke David A.
Published: October 2006

Numerical simulations with supercomputers allow analysis of the wide range of nonlinear physics inherent in the hydrodynamic and magnetohydrodynamic equations. When applied to extragalactic radio sources, these numerical models have begun to reproduce many of the complex structures observed on telescopic images. This combination of telescopic and numerical observations provides powerful probes of the physics of radio galaxies. In this review, some of the recent results from both two-dimensional and three-dimensional numerical simulations of the formation and evolution of extended radio morphologies are described. These numerical models have allowed the exploration of important physical phenomena including the role of magnetic fields in the dynamics and emissivity of extended radio galaxies, intermittent outflow from the cores of active galaxies, instabilities and disruption of fluid jets, and the bending of collimated outflows by motion through the intergalactic medium.
Formation of Fullerides and Fullerene-Based Heterostructures
Authors: Poirier D. M. , Ohno T. R. , Kroll G. H. , Chen Y. , Benning P. J. , Weaver J. H. , Chibante L. P. F. , Smalley R. E.
Published: October 2006

Two potassium fulleride phases, metallic K
3
C
60
and nonmetallic K
6
C
60
, are formed when potassium is incorporated into thin C
60
films under ultrahigh vacuum conditions. Phase separation is observed for intermediate stoichiometries. Results obtained for the C
60
-K
3
C
60
heterostructure demonstrate that it is stable against potassium migration from the K
3
C
60
phase. In contrast, the C
60
-K
6
C
60
interface is not stable and K
3
C
60
is formed.
elk
, Tissue-Specific
ets
-Related Genes on Chromosomes X and 14 Near Translocation Breakpoints
Authors: Rao Veena N. , Huebner Kay , Isobe Masaharu , ar-Rushdi Abbas , Croce Carlo M. , Reddy Shyam P.
Published: October 2006

The
myb
-
ets
-containing acute leukemia virus, E26, transforms myeloblasts and erythroblasts in culture and causes a mixed erythroid and myeloid leukemia in chicks. Genes (
ets
-1,
ets
-2, and
erg
) with variable relatedness to the v-
ets
oncogene of the E26 virus have been identified, cloned, and characterized in several species. Two new members (
elk
-1 and
elk
-2) of the
ets
oncogene superfamily have now been identified. Nucleotide sequence analysis of the
elk
-1 cDNA clone revealed that this gene encodes a 428-residue protein whose predicted amino acid sequence showed 82% similarity to the 3′ region of v-
ets
. The
elk
or related sequences appear to be transcriptionally active in testis and lung. The
elk
cDNA probe detects two loci in the human genome,
elk
-1 and
elk
-2, which map to chromosome regions Xp11.2 and 14q32.3, respectively. These loci are near the translocation breakpoint seen in the t(X;18) (p11.2;q11.2), which is characteristic of synovial sarcoma, and the chromosome 14q32 breakpoints seen in ataxia telangiectasia and other T cell malignancies. This suggests the possibility that rearrangements of
elk
loci may be involved in pathogenesis of certain tumors.
Latitudinal and Longitudinal Oscillations of Cloud Features on Neptune
Authors: Sromovsky Lawrence A.
Published: October 2006

Voyager observations suggest that three of Neptune's major cloud features oscillate in latitude by 2° to 4° and that two of them simultaneously oscillate in longitude by 7.8° and 98° about their mean drift longitudes. The observations define most convincingly the two orthogonal oscillations of the second dark spot (near 53° south). These oscillations have similar periods near 800 hours and approximately satisfy a simple advective model in which a latitudinal oscillation produces a phase-shifted longitudinal oscillation proportional to the local wind shear. The latitudinal motion of the Great Dark Spot can be fit with an oscillation period of about 2550 hours, whereas its dominant longitudinal motion, if oscillatory at all, has such a long period that it is not well constrained by the Voyager data.
X-ray Damage to CF
3
CO
2
-Terminated Organic Monolayers on Si/Au: Principal Effect of Electrons
Authors: Laibinis Paul E. , Graham Robert L. , Biebuyck Hans A. , Whitesides George M.
Published: October 2006

The relative importance of x-rays alone and of x-ray-generated primary and secondary electrons in damaging organic materials was explored by use of self-assembled monolayers (SAMs) on multilayer thin-film supports. The substrates were prepared by the deposit of thin films of silicon (0, 50, 100, and 200 angstroms) on thick layers of gold (2000 angstroms). These systems were supported on chromium-primed silicon wafers. Trifluoroacetoxy-terminated SAMs were assembled on these substrates, and the samples were irradiated with common fluxes of monochromatic aluminum K
α
x-rays. The fluxes and energy distributions of the electrons generated by interactions of the x-rays with the various substrates, however, differed. The substrates that emitted a lower flux of electrons exhibited a slower loss of fluorine from the SAMs. This observation indicated that the electrons—and not the x-rays themselves—were largely responsible for the damage to the organic monolayer.
Subterranean Waterworks of Biblical Jerusalem: Adaptation of a Karst System
Authors: Gill Dan
Published: October 2006

Ancient Jerusalem has long been known to possess a system of subterranean waterworks by which the spring of Gihon, which issues outside the walls, could be approached from within the city, and its waters diverted to an intramural pool. Most scholars regarded these waterworks as man-made, but the techniques of underground orientation and ventilation employed by the builders, as well as the numerous anomalies and ostensible mistakes in design, mystified investigators. Geological investigation has revealed the waterworks to be part of a well-developed karst system, a network of natural dissolution channels and shafts, in the limestone and dolomite underlying the city. Thus, it was not through primary planning but by means of skillful adaptation of these pre-existing natural features that the city was ensured of a dependable water supply during both war and peace. Likewise, knowledge of the subterranean access may have played a role in David's capture of the Jebusite city.
Electrical Resistivity and Stoichiometry of K
χ
C
60
Films
Authors: Kochanski G. P. , Hebard A. F. , Haddon R. C. , Fiory A. T.
Published: October 2006

Electrical resistances of polycrystalline fullerene (C
60
) films were monitored while the films were being doped in ultrahigh vacuum with potassium from a molecular-beam effusion source. Temperature- and concentration-dependent resistivities of K

x

C
60
films in equilibrium near room temperature were measured. The resistance changes smoothly from metallic at
x
≈ 3 to activated as
x
→ 0 or
x
→ 6. The minimum resistivity for K
3
C
60
films is 2.2 milliohm-centimeters, near the Mott limit. The resistivities are interpreted in terms of a granular microstructure where K
3
C
60
regions form nonpercolating grains, except perhaps at
x
≈ 3. Stoichiometries at the resistivity extrema were determined by ex situ Rutherford backscattering spectrometry to be
x
= 3 ± 0.05 at the resistance minimum and
x
= 6 ± 0.05 at the fully doped resistance maximum.
New Mechanism of Nonequilibrium Polymer Adsorption
Authors: Johnson Harry E. , Granick Steve
Published: October 2006

Nonequilibrium states of surface composition can be extremely long-lived when polymer chains adsorb competitively. In a model system (polymethylmethacrylate adsorbed from CCl
4
onto oxidized silicon previously saturated with polystyrene), it is shown that a weakly adsorbing polymer was sterically pinned to a surface by a more strongly adsorbing polymer. The dynamical evolution of the surface composition was strongly nonexponential in time and non-Arrhenius in temperature; the phenomenology is analogous to bulk glasses. This interpretation offers a new mechanism to explain why weakly adsorbing chains may bind to surfaces, as well as a direction in which to look for a method to release them.
Identification of a Naturally Occurring Transforming Variant of the p65 Subunit of NF-κB
Authors: Narayanan Ramaswamy , Klement John F. , Ruben Steven M. , Higgins Kimberly A. , Rosen Craig A.
Published: October 2006

Transcription factor NF-κB comprises two proteins, p50 and p65, that have sequence similarity to the v-
rel
oncogene. In primary hematopoietic cell populations an alternatively spliced form of NF-κB p65 mRNA was observed that encoded a protein designated p65Δ. Expression of the p65Δ cDNA in Rat-1 fibroblasts resulted in focus formation, anchorage-independent growth in soft agar, and tumor formation in athymic nude mice, effects not obtained with expression of p65 or a p65Δ mutant that contains a disruption within the transcriptional activation domain. Thus, p65Δ, which associated weakly and interfered with DNA binding by p65, may sequester an essential limiting regulatory factor or factors required for NF-κB function.
Bond Selectivity in Silicon Film Growth
Authors: Boland John J. , Parsons Gregory N.
Published: October 2006

Hydrogen atoms can selectively eliminate strained bonds that form during the growth of amorphous silicon films. By periodically interrupting the growth and exposing the grown material to hydrogen, the film composition can be varied continuously from a non-equilibrium amorphous structure to that of a crystalline solid. Furthermore, by tuning the hydrogen exposure it is possible to discriminate between Si—Si bonds formed on different substrates, thereby allowing substrate-selective growth. The evolution of the film structure during hydrogen exposure is directly observed by scanning tunneling microscopy, and a model describing the role of hydrogen is presented.
Chromosome Mapping and Expression of a Putative Testis-Determining Gene in Mouse
Authors: Nagamine Claude M. , Chan Kaimin , Kozak Christine A. , Lau Yun-Fat
Published: October 2006

Isolation and mapping of a mouse complementary DNA sequence (mouse Y-finger) encoding a multiple, potential zinc-binding, finger protein homologous to the candidate human testis-determining factor gene is reported. Four similar sequences were identified in Hind III-digested mouse genomic DNA. Two (7.2 and 2.0 kb) were mapped to the Y chromosome. Only the 2.0-kb fragment, however, was correlated with testis determination. Polymerase chain reaction analysis suggests both Y loci are transcribed in adult testes. A 3.6-kb fragment was mapped to the X chromosome between the T16H and T6R1 translocation breakpoints, and a fourth (6.0 kb) was mapped to chromosome 10. Hence, mYfin sequences have been duplicated several times in the mouse, although they are not duplicated in humans.
A Truncated Erythropoietin Receptor That Fails to Prevent Programmed Cell Death of Erythroid Cells
Authors: Nakamura Yukio , Komatsu Norio , Nakauchi Hiromitsu
Published: October 2006

A form of the human erythropoietin receptor (EPOR) was identified in which the cytoplasmic region is truncated by alternative splicing. The truncated form of the receptor (EPOR-T) is the most prevalent form of EPOR in early-stage erythroid progenitor cells, but the full-length EPOR (EPOR-F) becomes the most prevalent form in late-stage progenitors. EPOR-T can transduce a mitogenic signal. However, cells transfected with EPOR-T are more prone to programmed cell death than those expressing EPOR-F. EPOR-F may transduce a signal to prevent programmed cell death that is independent of the mitogenic signal, and alternative splicing of the EPOR gene may have an important role in erythropoiesis.
The Protein Kinase Domain of the ANP Receptor Is Required for Signaling
Authors: Chinkers Michael , Garbers David L.
Published: October 2006

A plasma membrane form of guanylate cyclase is a cell surface receptor for atrial natriuretic peptide (ANP). In response to ANP binding, the receptor-enzyme produces increased amounts of the second messenger, guanosine 3′,5′-monophosphate. Maximal activation of the cyclase requires the presence of adenosine 5′-triphosphate (ATP) or nonhydrolyzable ATP analogs. The intracellular region of the receptor contains at least two domains with homology to other proteins, one possessing sequence similarity to protein kinase catalytic domains, the other to regions of unknown function in a cytoplasmic form of guanylate cyclase and in adenylate cyclase. It is now shown that the protein kinase-like domain functions as a regulatory element and that the second domain possesses catalytic activity. When the kinase-like domain was removed by deletion mutagenesis, the resulting ANP receptor retained guanylate cyclase activity, but this activity was independent of ANP and its stimulation by ATP was markedly reduced. A model for signal transduction is suggested in which binding of ANP to the extracellular domain of its receptor initiates a conformational change in the protein kinase-like domain, resulting in derepression of guanylate cyclase activity.
Accumulation of Suspended Barite at Mesopelagic Depths and Export Production in the Southern Ocean
Authors: Dehairs Frank , Baeyens Willy , Goeyens Leo
Published: October 2006

The relation between the accumulation of barite (BaSO
4
) microcrystals in suspended matter from the mesopelagic depth region (100 to 600 meters) and the type of production in the euphotic layer (new versus recycled) was studied for different Southern Ocean environments. Considerable subsurface barite accumulated in waters characterized by maintained new production and limited grazing pressure during the growth season. On the other hand, little if any barite accumulated in areas where relatively large amounts of photosynthetically fixed carbon were transferred to the microheterotrophic community and where recycled production became predominant.
Synthesis of Two-Dimensional Polymers
Authors: Stupp S. I. , Son S. , Lin H. C. , Li L. S.
Published: October 2006

A synthetic pathway is described to construct "in bulk" two-dimensional (2D) polymers shaped as molecular sheets. A chiral oligomeric precursor is used that contains two reactive sites, a polymerizable group at one terminus and a reactive stereogenic center near the middle of the molecule. The bulk reaction yields bilayer 2D polymers of molecular weight in the order of millions and a monodisperse thickness of 50.2 angstroms. The 2D molecular objects form through molecular recognition by the oligomers, which self-organize into layers that place the reactive groups within specific planes. The oligomers become catenated by two different stitching reactions involving the reactive sites. At room temperature, stacks of these molecular objects can organize as single crystals and at higher temperatures melt into smectic liquid crystals. Nonlinear optical experiments reveal that solid films containing the 2D polymers form structures that are thermally and temporally more stable than those containing analogous 1D polymers. This observation suggests that the transformation of common polymers from a 1D to a 2D architecture may produce generations of organic materials with improved properties.
Rates of Electron Emission from Negatively Charged, Impact-Heated Fullerenes
Authors: Yeretzian Chahan , Hansen Klavs , Whetten Robert L.
Published: October 2006

Thermal emission of electrons is ordinarily considered to be exclusively a property of macroscopic condensed matter. Slow electron emission occurs for certain small metal clusters as well as for silicon and carbon clusters, but the nature of this process has not been established. Electron emission rates have been obtained and analyzed from extensive real-time measurements on negatively charged fullerenes for several sizes and over a wide, continuous range of energies. These results confirm that delayed electron emission is a simple activated process that depends strongly on the internal energy and size of the cluster and that it has a common underlying mechanism, independent of size. However, the Arrhenius form deduced is inconsistent with the emission rate theory used for bulk surfaces. These results allow the question of the correct microscopic description of this newly observed electron emission process to be assessed.
A Photomicrodynamic System with a Mechanical Resonator Monolithically Integrated with Laser Diodes on Gallium Arsenide
Authors: Ukita Hiroo , Uenishi Yuji , Tanaka Hidenao
Published: October 2006

A cantilever resonant microbeam, laser diodes, and a photodiode have been fabricated on the surface of a gallium arsenide substrate. The microbeam is excited photothermally by light from a laser diode. The vibration is detected with a photodiode as the variation in light output caused by the difference in optical length between the microbeam and another laser diode. A high carrier-to-noise ratio (45 decibels) is achieved with a short (3 micrometers) external cavity length. Such a small distance allows a lensless system, which increases the ease of fabrication. This work could lead to applications in which photomicrodynamic systems are monolithically integrated on a gallium arsenide substrate with surface micromachining technology.
Controlled Deposition, Soft Landing, and Glass Formation in Nanocluster-Surface Collisions
Authors: Cheng Hai-Ping , Landman Uzi
Published: October 2006

Molecular dynamics simulations have been used to investigate the dynamics and redistribution of energy during the impact of a nanocrystal with adsorbed liquid films. Although impact of a 32-molecule NaCl cluster on a solid surface at 3 kilometers per second leads to melting, disordering, fragmentation, and rebounding, the same size cluster colliding with a liquid neon film transfers its energy efficiently to the liquid for a controlled soft landing. Impact on a higher density film (argon) leads to rapid attenuation of the cluster velocity, accompanied by fast heating. Subsequent disordering, melting, and fast cooling by evaporation of argon quench the cluster to a glassy state. These results suggest a method for the controlled growth of nanophase materials.
Interlayer Tunneling and Gap Anisotropy in High-Temperature Superconductors
Authors: Chakravarty Sudip , Sudbø Asle , Anderson Philip W. , Strong Steven
Published: October 2006

A quantitative analysis of a recent model of high-temperature superconductors based on an interlayer tunneling mechanism is presented. This model can account well for the observed magnitudes of the high transition temperatures in these materials and implies a gap that does not change sign, can be substantially anisotropic, and has the same symmetry as the crystal. The experimental consequences explored so far are consistent with the observations.
Parallel Scientific Computation
Authors: Hillis W. Daniel , Boghosian Bruce M.
Published: October 2006

Massively parallel computers offer scientists a new tool for computation, with capabilities and limitations that are substantially different from those of traditional serial computers. Most categories of large-scale scientific computations have proven remarkably amenable to parallel computation, but often the algorithms involved are different from those used on sequential machines. By surveying a range of examples of parallel scientific computations, this article summarizes our current understanding of the issues of applicability and programming of parallel computers for scientific applications.
Probing Chemical Reactions: Evidence for Exploration of an Excited Potential Energy Surface at Thermal Energies
Authors: Barnes Michael D. , Brooks Philip R. , Curl R. F. , Johnson Bruce R.
Published: October 2006

The reaction K + NaBr → KBr + Na is probed during the reactive collision by a continuous wave laser tuned to frequencies not resonant with excitation in either reagents or products. Transient [K⋅⋅Br⋅⋅Na] absorbs a laser photon giving [K⋅⋅Br⋅⋅Na]
*
, which can decompose to Na
*
+ KBr. Emission from excited Na
*
at the sodium
D
lines provides direct evidence of laser absorption during the reaction. Different excitation spectra were observed, depending on which sodium
D
line was monitored. This difference is explicable if, in the absence of the laser, the reaction flux partially bifurcates to a second potential energy surface during the reaction.
Quantum Confinement in Size-Selected, Surface-Oxidized Silicon Nanocrystals
Authors: Wilson William L. , Szajowski P. F. , Brus L. E.
Published: October 2006

The dynamics and spectroscopy of silicon nanocrystals that emit at visible wavelengths were analyzed. Size-selective precipitation and size-exclusion chromatography cleanly separate the silicon nanocrystals from larger crystallites and aggregates and provide direct evidence for quantum confinement in luminescence. Measured quantum yields are as high as 50 percent at low temperature, principally as a result of efficient oxide passivation. Despite a 0.9—electron-volt shift of the band gap to higher energy, the nanocrystals behave fundamentally as indirect gap materials with low oscillator strength.
Photon Tunneling Microscopy of Polymeric Surfaces
Authors: Guerra John M. , Srinivasarao Mohan , Stein Richard S.
Published: October 2006

With photon tunneling microscopy it is possible to image polymeric and other dielectric surfaces by means of the unusual properties of photon tunneling or evanescent waves. Vertical resolution is 1 nanometer, limited by the detector, over a vertical range of half a wavelength. Lateral resolution is better than a quarter of a wavelength over a field of view up to 125 micrometers. Samples can be surveyed in real time in air, with no need for metallization, and without shadowing or the intrusive effects of electrons or scanning probes. The use of this technique to study single crystals of polyethylene and processes such as latex film formation and the evolution of polystyrene topography while dewetting above the glass transition temperature are described.
Upper Limit of 3.3 Astronomical Units to the Diameter of the Galactic Center Radio Source Sgr A
*
Authors: Backer D. C. , Zensus J. A. , Kellermann K. I. , Reid M. , Moran J. M. , Lo K. Y.
Published: October 2006

Sagittarius (Sgr) A
*
is a unique radio source located at the center of our galaxy. The radiation from Sgr A
*
may be generated in matter accreting onto a massive black hole. In observations at long wavelengths, the apparent angular size of Sgr A
*
decreases in the manner expected for emission from a point source scattered by electron density fluctuations along the line of sight. Measurements at a wavelength of 7 millimeters with the nearly completed Very Long Baseline Array indicate a size of 0.7 milliarc seconds, which is consistent with an extrapolation from results at longer wavelengths. The true size of Sgr A
*
must be less than 0.4 milliarc seconds, or 3.3 astronomical units. The inferred black hole mass is less than 1.5 × 10
6
solar masses according to a recent model for the emission.
Human Chromosome 12 Is Required for Elevated HIV-1 Expression in Human-Hamster Hybrid Cells
Authors: Hart Clyde E. , Ou Chin-Yih , Galphin Judith C. , Moore Jennifer , Bacheler Lee T. , Wasmuth John J. , Petteway Steven R. , Schochetman Gerald
Published: October 2006

Host cell factors act together with regulatory genes of the human immunodeficiency virus (HIV) to control virus production. Human-Chinese hamster ovary hybrid cell clones were used to probe for human chromosomes involved in regulating HIV gene expression. DNA transfection experiments showed that 4 of 18 clones had high levels of HIV gene expression measured by both extracellular virus production and transactivation of the HIV long terminal repeat in the presence of the trans-activator (
tat
) gene. Karyotype analyses revealed a 94% concordance (17/18) between human chromosome 12 and HIV gene expression. Other chromosomes had an 11 to 72% concordance with virus production.
Functional Analysis of CAR, the Target Sequence for the Rev Protein of HIV-1
Authors: Dayton Elahe T. , Powell Douglas M. , Dayton Andrew I.
Published: October 2006

Expression of high levels of the structural proteins of the human immunodeficiency virus type 1 (HIV-1) requires the presence of the protein encoded by the
rev
open reading frame (Rev) and its associated target sequence CAR (cis anti-repression sequence) which is present in the env region of viral RNA. Extensive mutagenesis demonstrated that CAR has a complex secondary structure consisting of a central stem and five stem/loops. Disruption of any of these structures severely impaired the Rev response, but many of the stem/loops contain material that was unnecessary for Rev regulation and must be retained in these structures to avoid disturbing adjacent structures critical for CAR function. Probably no more than two of the described structural components are involved in sequence-specific recognition by regulatory proteins.
Oxidation-Reduction and the Molecular Mechanism of a Regulatory RNA-Protein Interaction
Authors: Hentze Matthias W. , Rouault Tracey A. , Harford Joe B. , Klausner Richard D.
Published: October 2006

Iron-responsive elements (IREs) are RNA motifs that have been identified within the 5′ untranslated region of ferritin messenger RNA and the 3′ untranslated region of transferrin receptor mRNA. A single IRE mediates iron-dependent control of ferritin translation, whereas multiple IREs are found in the region of the transferrin receptor mRNA responsible for iron-dependent control of mRNA stability. A cytosolic protein binds in vitro to the IREs of both mRNAs. The IRE-binding protein (IRE-BP) is shown to require free sulfhydryl groups for its specific interaction with the IRE. Treatment of lysates with reducing agents increases the binding activity, whereas agents that block sulfhydryls inhibit binding. Iron starvation, leading to decreased ferritin translation, results in increased binding activity, which is explained by an increase in the fraction of the IRE-BP that is in a fully reduced state.
Calicheamicin γ
1
I
and DNA: Molecular Recognition Process Responsible for Site-Specificity
Authors: Zein Nada , Poncin Marc , Nilakantan Ramaswamy , Ellestad George A.
Published: October 2006

Calicheamicin γ
1
I
is a recently discovered diyne-ene-containing antitumor antibiotic that cleaves DNA in a double-stranded fashion, a rarity among drugs, at specific sequences. It is proposed that the cutting specificity is due to a combination of the complementarity of the diyne-ene portion of the aglycone with DNA secondary structures and stabilization by association of the thiobenzoate-carbohydrate tail with the minor groove.
Potassium Channels in Cardiac Cells Activated by Arachidonic Acid and Phospholipids
Authors: Kim Donghee , Clapham David E.
Published: October 2006

Two types of potassium-selective channels activated by intracellular arachidonic acid or phosphatidylcholine have been found in neonatal rat atrial cells. In inside-out patches, arachidonic acid and phosphatidylcholine each opened outwardly rectifying potassium-selective channels with conductances of 160 picosiemens (
I
K⋅AA
) and 68 picosiemens (
I
K⋅PC
), respectively. These potassium channels were not sensitive to internally applied adenosine triphosphate (ATP), magnesium, or calcium. Lowering the intracellular
p
H from 7.2 to 6.8 or 6.4 reversibly increased
I
K⋅AA
channel activity three- or tenfold, respectively. A number of fatty acid derivatives were tested for their ability to activate
I
K⋅AA
. These potassium-selective channels may help explain the increase in potassium conductance observed in ischemic cells and raise the possibility that fatty acid derivatives act as second messengers.
Imaging of Memory-Specific Changes in the Distribution of Protein Kinase C in the Hippocampus
Authors: Olds James L. , Anderson Matthew L. , McPhie Donna L. , Staten Latonia D. , Alkon Daniel L.
Published: October 2006

Activation of protein kinase C (PKC) can mimic the biophysical effects of associative learning on neurons. Furthermore, classical conditioning of the rabbit nictitating membrane (a form of associative learning) produces translocation of PKC activity from the cytosolic to the membrane compartments of the CA1 region of the hippocampus. Evidence is provided here for a significant change in the amount and distribution of PKC within the CA1 cell field of the rabbit hippocampus that is specific to learning. This change is seen at 1 day after learning as focal increments of [
3
H]phorbol-12,13-dibutyrate binding to PKC in computer-generated images produced from coronal autoradiographs of rabbit brain. In addition, 3 days after learning, the autoradiographs suggest a redistribution of PKC within CA1 from the cell soma to the dendrites.
Inhibition of a Class C β-Lactamase by a Specific Phosphonate Monoester
Authors: Pratt R. F.
Published: October 2006

A phosphonate monoester,
m
carboxyphenyl phenylacetamidomethylphosphonate, has been found to be a specific inhibitor of the class C β-lactamase of
Enterobacter cloacae
P99. Inactivation is rapid (10
3
per second per molar concentration) and reactivation very slow (2.2 × 10
-6
per second). Apparently concerted with the inactivation, one equivalent (with respect to the enzyme) of
m
hydroxybenzoate is released. Reactivation is accelerated by hydroxylamine and benzohydroxamate. This suggests that the loss of enzyme activity is due to phosphonylation of an active site functional group. This discovery holds the promise of a new general class of β-lactamase inhibitors and, perhaps, antibiotics.
Labeling of Neural Cells by Gold-Filled Sendai Virus Envelopes Before Intracerebral Transplantation
Authors: Ardizzoni Susan C. , Michaels Allan , Arendash Gary W.
Published: October 2006

Gold-filled Sendai virus envelopes were fused with cell suspensions from the basal forebrain of fetal rat donors, and the resulting gold-labeled cells were transplanted into the neocortex of adult rat recipients. Not only did large numbers of labeled cells remain intact through 3 months in the neocortex, but sizable numbers migrated subcortically to the recipient's lesioned nucleus basalis region (a distance of 4 to 5 millimeters). Since this technique is capable of labeling most transplanted cells for long periods of time, it may be useful in determining the survival, migration, and connectivity of intracerebrally transplanted tissues.
HTLV-II Transactivation Is Regulated by the Overlapping
tax
/
rex
Nonstructural Genes
Authors: Rosenblatt Joseph D. , Cann Alan J. , Slamon Dennis J. , Smalberg Ira S. , Shah Neil P. , Fujii Joyce , Wachsman William , Chen Irvin S. Y.
Published: October 2006

The human T-cell leukemia virus (HTLV) types I and II have two nonstructural genes that are encoded in overlapping reading frames. One of these genes, known as
tax
, has been shown to encode a protein responsible for enhanced transcription (transactivation) from the viral long terminal repeats (LTRs). Genetic evidence indicates that the second nonstructural gene of HTLV-II, here designated
rex
, acts in trans to modulate
tax
gene-mediated transactivation in a concentration-dependent fashion. The
rex
gene may regulate the process of transactivation during the viral life cycle.
Concerted Nonsyntenic Allelic Loss in Human Colorectal Carcinoma
Authors: Law David J. , Olschwang Sylviane , Monpezat Jean-Philippe , Lefrançois Danielle , Jagelman David , Petrelli Nicholas J. , Thomas Gilles , Feinberg Andrew P.
Published: October 2006

Familial polyposis coli (FPC) is caused by an autosomal dominant gene on chromosome 5, and it has been proposed that colorectal cancer in the general population arises from loss or inactivation of the FPC gene, analogous to recessive tumor genes in retinoblastoma and Wilms' tumor. Since allelic loss can be erroneously scored in nonhomogeneous samples, tumor cell populations were first microdissected from 24 colorectal carcinomas, an additional nine cancers were engrafted in nude mice, and nuclei were flow-sorted from an additional two. Of 31 cancers informative for chromosome 5 markers, only 6 (19%) showed loss of heterozygosity of chromosome 5 alleles, compared to 19 of 34 (56%) on chromosome 17, and 17 of 33 (52%) on chromosome 18. Therefore, it appears that (i) FPC is a true dominant for adenomatosis but not a common recessive gene for colon cancer; and (ii) simple Mendelian models involving loss of alleles at a single locus may be inappropriate for understanding common human solid tumors.
Sevenless
, a Cell-Specific Homeotic Gene of
Drosophila
, Encodes a Putative Transmembrane Receptor with a Tyrosine Kinase Domain
Authors: Hafen Ernst , Basler Konrad , Edstroem Jan-Erik , Rubin Gerald M.
Published: October 2006

The determination of cell fates during the assembly of the ommatidia in the compound eye of
Drosophila
appears to be controlled by cell-cell interactions. In this process, the
sevenless
gene is essential for the development of a single type of photoreceptor cell. In the absence of proper
sevenless
function the cells that would normally become the R7 photoreceptors instead become nonneuronal cells. Previous morphological and genetic analysis has indicated that the product of the
sevenless
gene is involved in reading or interpreting the positional information that specifies this particular developmental pathway. The
sevenless
gene has now been isolated and characterized. The data indicate that
sevenless
encodes a transmembrane protein with a tyrosine kinase domain. This structural similarity between
sevenless
and certain hormone receptors suggests that similar mechanisms are involved in developmental decisions based on cell-cell interaction and physiological or developmental changes induced by diffusible factors.
A New Prosomatostatin-Derived Peptide Reveals a Pattern for Prohormone Cleavage at Monobasic Sites
Authors: Benoit Robert , Ling Nicholas , Esch Frederick
Published: October 2006

Cleavage of the peptide bonds of preprosomatostatin at basic residues near the carboxyl terminus yields somatostatin-14, somatostatin-28, and somatostatin-28 (1-12). However, little is known about the molecular forms derived from the amino terminal portion of the precursor, even though this part of the prohormone is highly conserved through evolution. By using an antibody against the amino terminus of prosomatostatin, a decapeptide with the structure Ala-Pro-Ser-Asp-Pro-Arg-Leu-Arg-Gln-Phe, corresponding to preprosomatostatin (25-34), was isolated from the endocrine portion of the rat stomach, the gastric antrum. The antral decapeptide may represent a bioactive product generated from prosomatostatin after a monobasic cleavage similar to that involved in the formation of somatostatin-28. In fact, a monobasic cleavage requires two basic residues and a domain containing nonpolar amino acids such as alanine or leucine, or both.
Scanning Tunneling Microscopy of Uncoated recA-DNA Complexes
Authors: Amrein M. , Dürr R. , Stasiak A. , Gross H. , Travaglini G.
Published: October 2006

Uncoated recA-DNA complexes were imaged with the scanning tunneling microscope (STM). The images, which reveal the right-handed helical structure of the complexes with subunits clearly resolved, are comparable in quality to STM images of metal-coated specimens. Possible conduction mechanisms that allow STM imaging of biological macromolecules are discussed.
The Fos Complex and Fos-Related Antigens Recognize Sequence Elements That Co ntain AP-1 Binding Sites
Authors: Franza B. Robert , Rauscher Frank J. , Josephs Steven F. , Curran Tom
Published: October 2006

The Fos protein complex and several Fos-related antigens bind directly or indirectly to a common sequence element that is similar to the consensus binding site for HeLa cell activator protein 1 (AP-1). This element is present in a negative regulatory sequence in the differentiation-sensitive adipocyte gene, aP2; in a transcriptional enhancer for the Gibbon ape leukemia virus; and in a region of the human immunodeficiency virus (HIV) long terminal repeat partially characterized as a negative regulatory element. The protein level and binding activity of Fos and Fos-related antigens increase rapidly after calcium ionophore treatment of a CD4
+
human lymphoblast cell line, H9. These data suggest that several proteins may associate with the AP-1 binding site. Moreover, temporally regulated control of the level of each protein could represent a mechanism for modulation of these putative mediators of gene expression.
Assembly of Functional U1 and U2 Human-Amphibian Hybrid snRNPs in
Xenopus laevis
oocytes
Authors: Pan Zhen-Qiang , Prives Carol
Published: October 2006

Oligonucleotides complementary to regions of U1 and U2 small nuclear RNAs (snRNAs), when injected into
Xenopus laevis
oocytes, rapidly induced the specific degradation of U1 and U2 snRNAs, respectively, and then themselves were degraded. After such treatment, splicing of simian virus 40 (SV40) late pre-mRNA transcribed from microinjected viral DNA was blocked in oocytes. If before introduction of SV40 DNA into oocytes HeLa cell U1 or U2 snRNAs were injected and allowed to assemble into small nuclear ribonucleoprotein particle (snRNP)-like complexes, SV40 late RNA was as efficiently spliced as in oocytes that did not receive U1 or U2 oligonucleotides. This demonstrates that oocytes can form fully functional hybrid U1 and U2 snRNPs consisting of human snRNA and amphibian proteins.
Deregulation of Interleukin-2 Receptor Gene Expression in HTLV-I-Induced Adult T-Cell Leukemia
Authors: Krönke Martin , Leonard Warren J. , Depper Joel M. , Greene Warner C.
Published: October 2006

Infection of human T cells by human T-lymphotropic virus, type I (HTLV-I), a retrovirus, is uniformly associated with the constitutive expression of large numbers of cellular receptors for interleukin-2 (IL-2). Comparison with normal T cells shows that neither IL-2 receptor gene organization nor IL-2 receptor messenger RNA processing are altered in the leukemic cells. However, mitogenic stimuli activate IL-2 receptor gene expression in normal T cells, whereas these stimuli paradoxically inhibit IL-2 receptor gene transcription in HTLV-I-infected leukemic T cells.
Studies of the Putative Transforming Protein of the Type I Human T-Cell Leukemia Virus
Authors: Slamon Dennis J. , Press Michael F. , Souza Lawrence M. , Murdock Douglas C. , Cline Martin J. , Golde David W. , Gasson Judith C. , Chen Irvin S. Y.
Published: October 2006

The putative transforming protein of the type I human T-cell leukemia virus (HTLV-I) is a 40-kilodalton protein encoded by the X region and is termed p40

xI

. On the basis of both subcellular fractionation techniques and immunocytochemical analysis, it is now shown that p40

xI

is a nuclear protein with a relatively short half-life (120 minutes). It is synthesized de novo in considerable quantities in a human T-cell line infected with and transformed by the virus in vitro, and it is not packaged in detectable amounts in the extracellular virus.
Imaging Elemental Distribution and Ion Transport in Cultured Cells with Ion Microscopy
Authors: Chandra Subhash , Morrison George H.
Published: October 2006

Both elemental distribution and ion transport in cultured cells have been imaged by ion microscopy. Morphological and chemical information was obtained with a spatial resolution of approximately 0.5 μm for sodium, potassium, calcium, and magnesium in freeze-fixed, cryofractured, and freeze-dried normal rat kidney cells and Chinese hamster ovary cells. Ion transport was successfully demonstrated by imaging Na
+
-K
+
fluxes after the inhibition of Na
+
- and K
+
-dependent adenosine triphosphatase with ouabain. This method allows measurements of elemental (isotopic) distribution to be related to cell morphology, thereby providing the means for studying ion distribution and ion transport under different physiological, pathological, and toxicological conditions in cell culture systems.
Cyclic AMP Regulation of Eukaryotic Gene Transcription by Two Discrete Molecular Mechanisms
Authors: Waterman Marian , Murdoch Geoffrey H. , Evans Ronald M. , Rosenfeld Michael G.
Published: October 2006

In experiments designed to study the mechanism by which peptide hormones binding to their plasma membrane receptors stimulate the expression of specific genes, the transcription of two neuroendocrine genes, prolactin and growth hormone, was analyzed in a rat pituitary cell line. The results showed that cyclic adenosine monophosphate (cyclic AMP) stimulates the transcription of discrete subsets of eukaryotic genes by at least two independent molecular mechanisms. Cyclic AMP stimulated growth hormone gene transcription and phosphorylation of a 19,000-dalton nuclear protein; this appears to reflect direct nuclear actions of the cyclic AMP-dependent protein kinase. In contrast, the stimulation by cyclic AMP of prolactin gene transcription appears to reflect activation of a discrete calcium-dependent event.
Contribution of Promoter to Tissue-Specific Expression of the Mouse Immunoglobulin Kappa Gene
Authors: Gopal T. Venkat , Shimada Takashi , Baur Anne W. , Nienhuis Arthur W.
Published: October 2006

The immunoglobulin kappa (κ) gene promoter was activated by a "neutral" enhancer derived from Harvey murine sarcoma virus (HaMuSV) in immunoglobulin-producing myeloma cells, regardless of the enhancer's orientation or position in the vector. In one fibroblast line (3T3) the immunoglobulin κ gene promoter was completely inactive when linked to the HaMuSV enhancer, whereas in mouse L cells, promoter activity was observed only with the HaMuSV enhancer in tandem with the immunoglobulin κ gene promoter. The differential behavior of the gene promoter, when activated by a neutral enhancer in these three murine cell lines, suggests that promoter sequences contribute to the tissue-specific expression of this gene.