bluuebunny/crossref_metadata_2025 huggingface dataset:
Plasma Observations at Venus with Galileo
Authors: Frank L. A. , Paterson W. R. , Ackerson K. L. , Coroniti F. V. , Vasyliunas V. M.
Published: October 2006

Plasma measurements were obtained with the Galileo spacecraft during an approximately 3.5-hour interval in the vicinity of Venus on 10 February 1990. Several crossings of the bow shock in the local dawn sector were recorded before the spacecraft passed into the solar wind upstream from this planet. Although observations of ions of the solar wind and the postshock magnetosheath plasmas were not possible owing to the presence of a sunshade for thermal protection of the instrument, solar wind densities and bulk speeds were determined from the electron velocity distributions. A magnetic field—aligned distribution of hotter electrons or ''strahl'' was also found in the solar wind. Ions streaming into the solar wind from the bow shock were detected. Electron heating at the bow shock, ≤20%, was notably small, with substantial density increases by factors of 2 to 3 at the day side of the shock that decrease for shock crossings further downstream from the planet. A search for pickup ions from the hot hydrogen and oxygen planetary coronas yielded an upper limit for these densities in the range of 10
-3
ion per cubic centimeter, which is consistent with densities expected from current models of neutral gas densities.
Transformation and Plasmacytoid Differentiation of EBV-Infected Human B Lymphoblasts by
ras
Oncogenes
Authors: Seremetis Stephanie , Inghirami Giorgio , Ferrero Dario , Newcomb Elizabeth W. , Knowles Daniel M. , Dotto Gian-Paolo , Dalla-Favera Riccardo
Published: October 2006

The biological effects of
ras
oncogene activation in B cells were studied by using amphotropic retroviral vectors to introduce H- or N-
ras
oncogenes into human B lymphoblasts immortalized by Epstein-Barr virus. Expression of both H- and N-
ras
oncogenes led to malignant transformation of these cells, as shown by clonogenicity in semisolid media and tumorigenicity in immunodeficient mice. In addition, terminal differentiation into plasma cells was detectable as specific changes in morphology, immunoglobulin secretion, and cell surface antigen expression. This combined effect, promoting growth and differentiation in human lymphoblasts, represents a novel biological action of
ras
oncogenes and has implications for the pathogenesis of terminally differentiated B-lymphoid malignancies such as multiple myeloma.
Molecular Modeling of the HIV-1 Protease and Its Substrate Binding Site
Authors: Weber Irene T. , Miller Maria , Jaskólski Mariusz , Leis Jonathan , Skalka Anna Marie , Wlodawer Alexander
Published: October 2006

The human immunodeficiency virus (HIV-1) encodes a protease that is essential for viral replication and is a member of the aspartic protease family. The recently determined three-dimensional structure of the related protease from Rous sarcoma virus has been used to model the smaller HIV-1 dimer. The active site has been analyzed by comparison to the structure of the aspartic protease, rhizopuspepsin, complexed with a peptide inhibitor. The HIV-1 protease is predicted to interact with seven residues of the protein substrate. This information can be used to design protease inhibitors and possible antiviral drugs.
Activity-Dependent Enhancement of Presynaptic Inhibition in
Aplysia
Sensory Neurons
Authors: Small S. A. , Kandel E. R. , Hawkins R. D.
Published: October 2006

Tail shock produces transient presynaptic inhibition and longer lasting presynaptic facilitation of the siphon sensory neurons in
Aplysia
. The facilitation undergoes activity-dependent enhancement that is thought to contribute to classical conditioning of the gill- and siphon-withdrawal reflex. Inhibition of the sensory neurons has now also been shown to undergo activity-dependent enhancement when action potential activity in the sensory neurons is paired with inhibitory transmitter. This effect appears to involve an amplification of the same cellular mechanisms that are involved in normal presynaptic inhibition. These results suggest that activity-dependent enhancement may be a general type of associative cellular mechanism.
Limbic Seizures Increase Neuronal Production of Messenger RNA for Nerve Growth Factor
Authors: Gall Christine M. , Isackson Paul J.
Published: October 2006

Nerve growth factor (NGF) produced by telencephalic neurons provides critical trophic support for cholinergic neurons of the basal forebrain. In situ hybridization and nuclease protection analyses demonstrate that limbic seizures dramatically increase the amount of messenger RNA for NGF in the neurons of the hippocampal dentate gyrus within 1 hour of seizure onset and in broadly distributed neocortical and olfactory forebrain neurons some hours later. The increased messenger RNA species is indistinguishable from messenger RNA for transcript B of the β subunit of NGF from mouse submandibular gland. Thus, the expression of a known growth factor is affected by unusual physiological activity, suggesting one route through which trophic interactions between neurons in adult brain can be modified.
Compressibility of M3C60Fullerene Superconductors: Relation BetweenTcand Lattice Parameter
Authors: Zhou Otto , Zhu Qing , Fischer John E. , Coustel Nicole , Vaughan Gavin B. M. , Heiney Paul A. , McCauley John P. , Smith Amos B.
Published: October 2006

X-ray diffraction and diamond anvil techniques were used to measure the isothermal compressibility of K3C60and Rb3C60, the superconducting, binary alkali-metal intercalation compounds of solid buckminsterfullerene. These results, combined with the pressure dependence of the superconducting onset temperatureTcmeasured by other groups, establish a universal first-order relation betweenTcand the lattice parameteraover a broad range, between 13.9 and 14.5 angstroms. A small second-order intercalate-specific effect was observed that appears to rule out the participation of intercalate-fullerene optic modes in the pairing interaction.
Early Evolution of Avian Flight and Perching: New Evidence from the Lower Cretaceous of China
Authors: Sereno Paul C. , Chenggang Rao
Published: October 2006

Fossil bird skeletons discovered in Lower Cretaceous lake deposits in China shed new light on the early evolution of avian flight and perching. The 135 million-year-old sparrow-sized skeletons represent a new avian,
Sinornis santensis
, n. gen. n. sp., that preserves striking primitive features such as a flexible manus with unguals, a footed pubis, and stomach ribs (gastralia). In contrast to
Archaeopteryx
, however,
Sinornis
exhibits advanced features such as a broad sternum, wing-folding mechanism, pygostyle, and large fully reversed hallux. Modern avian flight function and perching capability, therefore, must have evolved in small-bodied birds in inland habitats not long after
Archaeopteryx
.
Calcium-Regulated Phosphorylation Within the Leucine Zipper of C/EBPβ
Authors: Wegner Michael , Cao Zhaodan , Rosenfeld Michael G.
Published: October 2006

Alterations in intracellular calcium levels activate several signal transduction pathways resulting in distinct patterns of gene expression. Here, a pathway for calcium-mediated signals is demonstrated that involves C/EBPβ, a member of the bZip family of transcription factors. In pituitary cells C/EBPβ was phosphorylated in response to increased intracellular calcium concentrations as a consequence of the activation of a calcium-calmodulin— dependent protein kinase. Phosphorylation of serine at position 276 within the leucine zipper of C/EBPβ appeared to confer calcium-regulated transcriptional stimulation of a promoter that contained binding sites for C/EBPβ.
Molecular Epidemiology of HIV Transmission in a Dental Practice
Authors: Ou Chin-Yih , Ciesielski Carol A. , Myers Gerald , Bandea Claudiu I. , Luo Chi-Cheng , Korber Bette T. M. , Mullins James I. , Schochetman Gerald , Berkelman Ruth L. , Economou A. Nikki , Witte John J. , Furman Lawrence J. , Satten Glen A. , Maclnnes Kersti A. , Curran James W. , Jaffe Harold W. ,   Laboratory Investigation Group,   Epidemiologic Investigation Group
Published: October 2006

Human immunodeficiency virus type 1 (HIV-1) transmission from infected patients to health-care workers has been well documented, but transmission from an infected healthcare worker to a patient has not been reported. After identification of an acquired immunodeficiency syndrome (AIDS) patient who had no known risk factors for HIV infection but who had undergone an invasive procedure performed by a dentist with AIDS, six other patients of this dentist were found to be HIV-infected. Molecular biologic studies were conducted to complement the epidemiologic investigation. Portions of the HIV proviral envelope gene from each of the seven patients, the dentist, and 35 HIV-infected persons from the local geographic area were amplified by polymerase chain reaction and sequenced. Three separate comparative genetic analyses—genetic distance measurements, phylogenetic tree analysis, and amino acid signature pattern analysis—showed that the viruses from the dentist and five dental patients were closely related. These data, together with the epidemiologic investigation, indicated that these patients became infected with HIV while receiving care from a dentist with AIDS.
Near-Field Optics: Microscopy, Spectroscopy, and Surface Modification Beyond the Diffraction Limit
Authors: Betzig Eric , Trautman Jay K.
Published: October 2006

The near-field optical interaction between a sharp probe and a sample of interest can be exploited to image, spectroscopically probe, or modify surfaces at a resolution (down to ∼12 nm) inaccessible by traditional far-field techniques. Many of the attractive features of conventional optics are retained, including noninvasiveness, reliability, and low cost. In addition, most optical contrast mechanisms can be extended to the near-field regime, resulting in a technique of considerable versatility. This versatility is demonstrated by several examples, such as the imaging of nanometric-scale features in mammalian tissue sections and the creation of ultrasmall, magneto-optic domains having implications for highdensity data storage. Although the technique may find uses in many diverse fields, two of the most exciting possibilities are localized optical spectroscopy of semiconductors and the fluorescence imaging of living cells.
Predatorial Borings in Late Precambrian Mineralized Exoskeletons
Authors: Bengtson Stefan , Zhao Yue
Published: October 2006

The late Precambrian tube-forming
Cloudina
, the earliest known animal to produce a mineralized exoskeleton, shows evidence of having been attacked by shell-boring organisms. Of more than 500 tubes from Shaanxi Province, China, 2.7% have rounded holes 40 to 400 micrometers in diameter. The relation between the size of the holes and the width of the bored tubes suggests that the attacking organism was a predator, selecting its prey for size. If true, this would be the oldest case of predation in the fossil record and would support the hypothesis that selection pressures from predation was a significant factor in the evolution of animal skeletons around the Precambrian-Cambrian boundary.
Ocean Warming and Sea Level Rise Along the Southwest U.S. Coast
Authors: Roemmich Dean
Published: October 2006

Hydrographic time-series data recorded during the past 42 years in the upper 500 meters off the coast of southern California indicate that temperatures have increased by 0.8°C uniformly in the upper 100 meters and that temperatures have risen significantly to depths of about 300 meters. The effect of warming the surface layer of the ocean and thereby expanding the water column has been to raise sea level by 0.9 ± 0.2 millimeter per year. Tide gauge records along the coast are coherent with steric height and show upward trends in sea level that vary from about 1 to 3 millimeters per year.
Innovation in San Francisco
Authors: Travis John
Published: October 2006

In San Francisco 2 weeks ago, AAAS and
Science
sponsored a new meeting, Science Innovation '92. The unusual gathering focused not on research results but on new techniques and instruments, particularly for biomedical science. As seen in the stories below, some of the most eye-catching innovations emerged at the intersection of physics and biology.
Coeval
40
Ar/
39
Ar Ages of 65.0 Million Years Ago from Chicxulub Crater Melt Rock and Cretaceous-Tertiary Boundary Tektites
Authors: Swisher Carl C. , Grajales-Nishimura José M. , Montanari Alessandro , Margolis Stanley V. , Claeys Philippe , Alvarez Walter , Renne Paul , Cedillo-Pardoa Esteban , Maurrasse Florentin J-M. R. , Curtis Garniss H. , Smit Jan , McWilliams Michael O.
Published: October 2006

40
Ar/
39
Ar dating of drill core samples of a glassy melt rock recovered from beneath a massive impact breccia contained within the 180-kilometer subsurface Chicxulub crater in Yucatán, Mexico, has yielded well-behaved incremental heating spectra with a mean plateau age of 64.98 ± 0.05 million years ago (Ma). The glassy melt rock of andesitic composition was obtained from core 9 (1390 to 1393 meters) in the Chicxulub 1 well. The age of the melt rock is virtually indistinguishable from
40
Ar/
39
Ar ages obtained on tektite glass from Beloc, Haiti, and Arroyo el Mimbral, northeastern Mexico, of 65.01 ± 0.08 Ma (mean plateau age for Beloc) and 65.07 ± 0.10 Ma (mean total fusion age for both sites). The
40
Ar/
39
Ar ages, in conjunction with geochemical and petrological similarities, strengthen the recent suggestion that the Chicxulub structure is the source for the Haitian and Mexican tektites and is a viable candidate for the Cretaceous-Tertiary boundary impact site.
Epidemiology of Drug Resistance: Implications for a Post—Antimicrobial Era
Authors: Cohen Mitchell L.
Published: October 2006

In the last several years, the frequency and spectrum of antimicrobial-resistant infections have increased in both the hospital and the community. Certain infections that are essentially untreatable have begun to occur as epidemics both in the developing world and in institutional settings in the United States. The increasing frequency of drug resistance has been attributed to combinations of microbial characteristics, selective pressures of antimicrobial use, and societal and technologic changes that enhance the transmission of drug-resistant organisms. Antimicrobial resistance is resulting in increased morbidity, mortality, and health-care costs. Prevention and control of these infections will require new antimicrobial agents, prudent use of existing agents, new vaccines, and enhanced public health efforts to reduce transmission.
The Role of Hemoglobin Denaturation and Band 3 Clustering in Red Blood Cell Aging
Authors: Low Philip S. , Waugh Stephen M. , Zinke Karen , Drenckhahn Detlev
Published: October 2006

As hemoglobin begins to denature, it forms hemichromes that cross-link the major erythrocyte membrane-spanning protein, band 3, into clusters. These clusters provide the recognition site for antibodies directed against senescent cells. These antibodies bind to the aged red cell and trigger its removal from circulation.
Observations of the Liquid-Crystal Analog of the Abrikosov Phase
Authors: Ihn K. J. , Zasadzinski J. A. N. , Pindak R. , Slaney A. J. , Goodby J.
Published: October 2006

Freeze-fracture transmission electron micrographs of the smectic A
*
phase confirm the twist grain boundary model of Renn and Lubensky. The fracture surface has an undulating structure with a 0.5-micrometer helical pitch parallel to 4.1-nanometer smectic layers. The layers are disrupted by a lattice of screw dislocations oriented normal to the helical axis. Optical diffraction shows that rotation of smectic blocks occurs in discrete steps of about 17°; hence, the screw dislocations are 14 to 15 nanometers apart and the grain boundaries are 24 nanometers apart. These observations show that the SmA
*
phase is the liquid-crystal analog of the Abrikosov phase in superconductors.
Complete Wetting from Polymer Mixtures
Authors: Steiner Ullrich , Klein Jacob , Eiser Erika , Budkowski Andrzej , Fetters Lewis J.
Published: October 2006

Coexisting polymer phases are characterized by very small interfacial energies, even well below their critical solution temperature. This situation should readily lead to the exclusion of one of the phases from any interface that favors the other. Such complete wetting behavior from a binary mixture of statistical olefinic copolymers is reported. By means of a self-regulating geometry, it is found that the thickness of a wetting layer of one of the phases at the polymer-air interface, growing from the other coexisting phase, attains macroscopic dimensions, increasing logarithmically with time. These results indicate that binary polymer mixtures could be attractive models for the study of wetting phenomena.
Manipulation of the Reconstruction of the Au(111) Surface with the STM
Authors: Hasegawa Y. , Avouris Ph.
Published: October 2006

Modification of the reconstruction of an Au(111) surface with a scanning tunneling microscope (STM) is demonstrated. This modification is accomplished by transferring a number of surface atoms to the STM tip to generate a surface multivacancy (hole), which modifies the stress distribution at the surface. The structural changes that follow the tip-induced surface perturbation are imaged in a time-resolved manner. The structural modification is the result of both short-range interactions, which lead to local atomic relaxation, and long-range elastic interactions, which produce large-scale rearrangements.
Mechanism Diversity of the Loma Prieta Aftershocks and the Mechanics of Mainshock-Aftershock Interaction
Authors: Beroza Gregory C. , Zoback Mark D.
Published: October 2006

The diverse aftershock sequence of the 1989 Loma Prieta earthquake is inconsistent with conventional models of mainshock-aftershock interaction because the aftershocks do not accommodate mainshock-induced stress changes. Instead, the sense of slip of the aftershocks is consistent with failure in response to a nearly uniaxial stress field in which the maximum principal stress acts almost normal to the mainshock fault plane. This orientation implies that (i) stress drop in the mainshock was nearly complete, (ii) mainshock-induced decreases of fault strength helped were important in controlling the occurrence of aftershocks, and (iii) mainshock rupture was limited to those sections of the fault with preexisting shear stress available to drive fault slip.
Export of North American Ozone Pollution to the North Atlantic Ocean
Authors: Parrish David D. , Holloway John S. , Trainer Michael , Murphy Paul C. , Fehsenfeld Fred C. , Forbes Gerry L.
Published: October 2006

Measurement of the levels of ozone and carbon monoxide (a tracer of anthropogenic pollution) at three surface sites on the Atlantic coast of Canada allow the estimation of the amount of ozone photochemically produced from anthropogenic precursors over North America and transported to the lower troposphere over the temperate North Atlantic Ocean. This amount is greater than that injected from the stratosphere, the primary natural source of ozone. This conclusion supports the contention that ozone derived from anthropogenic pollution has a hemisphere-wide effect at northern temperate latitudes.
Molecular Interactions and Hydrogen Bond Tunneling Dynamics: Some New Perspectives
Authors: Saykally Richard J. , Blake Geoffrey A.
Published: October 2006

The recent development of tunable far-infrared lasers and other high-resolution spectroscopic probes of weakly bound clusters is having a significant impact on our understanding of intermolecular forces and on the complex quantum tunneling dynamics that occur in hydrogen-bonded systems. Far-infrared studies of a variety of interactions are discussed, including several prototypical water-hydrophobe complexes, the water trimer, and the ammonia dimer. Particular attention is paid to the inversion of spectroscopic data to yield detailed intermolecular potential energy surfaces. Investigations of nonpairwise additivity are also described.
Coherent Control of Quantum Dynamics: The Dream Is Alive
Authors: Warren Warren S. , Rabitz Herschel , Dahleh Mohammed
Published: October 2006

Current experimental and theoretical progress toward the goal of controlling quantum dynamics is summarized. Two key developments have now revitalized the field. First, appropriate ultrafast laser pulse shaping capabilities have only recently become practical. Second, the introduction of engineering control concepts has put the required theoretical framework on a rigorous foundation. Extrapolations to determine what is realistically possible are presented.
Genetic Conversion of a Fungal Plant Pathogen to a Nonpathogenic, Endophytic Mutualist
Authors: Freeman Stanley , Rodriguez Rusty J.
Published: October 2006

The filamentous fungal ascomycete
Colletotrichum magna
causes anthracnose in cucurbit plants. Isolation of a nonpathogenic mutant of this species (path-1) resulted in maintained wild-type levels of in vitro sporulation, spore adhesion, appressorial formation, and infection. Path-1 grew throughout host tissues as an endophyte and retained the wild-type host range, which indicates that the genetics involved in pathogenicity and host specificity are distinct. Prior infection with path-1 protected plants from disease caused by
Colletotrichum
and
Fusarium
. Genetic analysis of a cross between path-1 and wild-type strains indicated mutation of a single locus.
Chips off of Asteroid 4 Vesta: Evidence for the Parent Body of Basaltic Achondrite Meteorites
Authors: Binzel Richard P. , Xu Shui
Published: October 2006

For more than two decades, asteroid 4 Vesta has been debated as the source for the eucrite, diogenite, and howardite classes of basaltic achondrite meteorites. Its basaltic achondrite spectral properties are unlike those of other large main-belt asteroids. Telescopic measurements have revealed 20 small (diameters ≤ 10 kilometers) main-belt asteroids that have distinctive optical reflectance spectral features similar to those of Vesta and eucrite and diogenite meteorites. Twelve have orbits that are similar to Vesta's and were previously predicted to be dynamically associated with Vesta. Eight bridge the orbital space between Vesta and the 3:1 resonance, a proposed source region for meteorites. These asteroids are most probably multikilometer-sized fragments excavated from Vesta through one or more impacts. The sizes, ejection velocities of 500 meters per second, and proximity of these fragments to the 3:1 resonance establish Vesta as a dynamically viable source for eucrite, diogenite, and howardite meteorites.
Ozone Loss Inside the Northern Polar Vortex During the 1991-1992 Winter
Authors: Proffitt M. H. , Aikin K. , Margitan J. J. , Loewenstein M. , Podolske J. R. , Weaver A. , Chan K. R. , Fast H. , Elkins J. W.
Published: October 2006

Measurements made in the outer ring of the northern polar vortex from October 1991 through March 1992 reveal an altitude-dependent change in ozone, with a decrease at the bottom of the vortex and a substantial increase at the highest altitudes accessible to measurement. The increase is the result of ozone-rich air entering the vortex, and the decrease reflects ozone loss accumulated after the descent of the air through high concentrations of reactive chlorine. The depleted air that is released out of the bottom of the vortex is sufficient to significantly reduce column ozone at mid-latitudes.
Ozone and Aerosol Changes During the 1991-1992 Airborne Arctic Stratospheric Expedition
Authors: Browell Edward V. , Butler Carolyn F. , Fenn Marta A. , Grant William B. , Ismail Syed , Schoeberl Mark R. , Toon Owen B. , Loewenstein Max , Podolske James R.
Published: October 2006

Stratospheric ozone and aerosol distributions were measured across the wintertime Arctic vortex from January to March 1992 with an airborne lidar system as part of the 1992 Airborne Arctic Stratospheric Expedition (AASE II). Aerosols from the Mount Pinatubo eruption were found outside and inside the vortex with distinctly different distributions that clearly identified the dynamics of the vortex. Changes in aerosols inside the vortex indicated advection of air from outside to inside the vortex below 16 kilometers. No polar stratospheric clouds were observed and no evidence was found for frozen volcanic aerosols inside the vortex. Between January and March, ozone depletion was observed inside the vortex from 14 to 20 kilometers with a maximum average loss of about 23 percent near 18 kilometers.
Physical Chemistry of the H
2
SO
4
/HNO
3
/H
2
O System: Implications for Polar Stratospheric Clouds
Authors: Molina M. J. , Zhang R. , Wooldridge P. J. , McMahon J. R. , Kim J. E. , Chang H. Y. , Beyer K. D.
Published: October 2006

Polar stratospheric clouds (PSCs) play a key role in stratospheric ozone depletion. Surface-catalyzed reactions on PSC particles generate chlorine compounds that photolyze readily to yield chlorine radicals, which in turn destroy ozone very efficiently. The most prevalent PSCs form at temperatures several degrees above the ice frost point and are believed to consist of HNO
3
hydrates; however, their formation mechanism is unclear. Results of laboratory experiments are presented which indicate that the background stratospheric H
2
SO
4
/H
2
O aerosols provide an essential link in this mechanism: These liquid aerosols absorb significant amounts of HNO
3
vapor, leading most likely to the crystallization of nitric acid trihydrate (NAT). The frozen particles then grow to form PSCs by condensation of additional amounts of HNO
3
and H
2
O vapor. Furthermore, reaction probability measurements reveal that the chlorine radical precursors are formed readily at polar stratospheric temperatures not just on NAT and ice crystals, but also on liquid H
2
SO
4
solutions and on solid H
2
SO
4
hydrates. These results imply that the chlorine activation efficiency of the aerosol particles increases rapidly as the temperature approaches the ice frost point regardless of the phase or composition of the particles.
SSZ-26 and SSZ-33: Two Molecular Sieves with Intersecting 10- and 12-Ring Pores
Authors: Lobo Raul F. , Pan Ming , Chan Ignatius , Li Hong-Xin , Medrud Ronald C. , Zones Stacey I. , Crozier Peter A. , Davis Mark E.
Published: October 2006

The framework structures of two closely related molecular sieves, SSZ-26 and SSZ-33, are described. These materials possess a previously missing but desired structural feature in a group of industrially significant zeolites. They contain a three-dimensional pore system that provides access to the crystal interior through both 10- and 12-rings. This property is a consequence of the organic structure—directing agents used in the synthesis of these materials. These materials are examples of the purposeful design of a micropore architecture. Both SSZ-26 and SSZ-33 contain the 4=4–1 building unit that had been previously found only in natural zeolites.
Superheating Effects on Metal-Silicate Partitioning of Siderophile Elements
Authors: Walker D. , Norby L. , Jones J. H.
Published: October 2006

Liquid metal—liquid silicate partition coefficients for several elements at 100 kilobars and temperatures up to about 3000 kelvin in carbon capsules experimentally converge on unity with increasing temperature. The sense of change of the partition coefficients with temperature resembles the extrapolation of Murthy and may partially contribute to, but by no means provide a complete resolution of, the "excess" siderophile problem in the Earth's mantle. Sulfur and perhaps carbon successfully compete with oxygen for sites in the metallic liquid at these temperatures and pressures. This observation casts doubt upon the hypothesis that oxygen is the light element in the Earth's core.
Altering the Genome by Homologous Recombination
Authors: Capecchi Mario R.
Published: October 2006

Homologous recombination between DNA sequences residing in the chromosome and newly introduced, cloned DNA sequences (gene targeting) allows the transfer of any modification of the cloned gene into the genome of a living cell. This article discusses the current status of gene targeting with particular emphasis on germ line modification of the mouse genome, and describes the different methods so far employed to identify those rare embryonic stem cells in which the desired targeting event has occurred.
Hydrophobic Organization of Membrane Proteins
Authors: Rees D. C. , DeAntonio L. , Eisenberg D.
Published: October 2006

Membrane-exposed residues are more hydrophobic than buried interior residues in the transmembrane regions of the photosynthetic reaction center from
Rhodobacter sphaeroides
. This hydrophobic organization is opposite to that of water-soluble proteins. The relative polarities of interior and surface residues of membrane and water soluble proteins are not simply reversed, however. The hydrophobicities of interior residues of both membrane and water-soluble proteins are comparable, whereas the bilayer-exposed residues of membrane proteins are more hydrophobic than the interior residues, and the aqueous-exposed residues of water-soluble proteins are more hydrophilic than the interior residues. A method of sequence analysis is described, based on the periodicity of residue replacement in homologous sequences, that extends conclusions derived from the known atomic structure of the reaction center to the more extensive database of putative transmembrane helical sequences.
Enhancement of Bacteriophage T4 Late Transcription by Components of the T4 DNA Replication Apparatus
Authors: Herendeen Daniel R. , Kassavetis George A. , Barry Jack , Alberts Bruce M. , Geiduschek E. Peter
Published: October 2006

The expression of the late genes in bacteriophage T4 development is closely connected to viral DNA replication. Three T4-encoded DNA polymerase accessory proteins are shown to stimulate transcription at T4 late promoters in an adenosine triphosphate (ATP) hydrolysis-requiring process. The properties of the activation resemble those found for enhancers of eukaryotic transcription. However, the nature of the enhancer of T4 late transcription is novel in that it is a structure—a break in the nontranscribed DNA stand—to which the three replication proteins bind, rather than a sequence. Since the three DNA polymerase accessory proteins are carried on the moving replication fork as part of the replisome, we postulate that viral DNA replication forks act, in vivo, as the mobile enhancers of T4 late gene transcription. Whereas
Escherichia coli
RNA polymerase bearing the T4 gene 55 protein can selectively recognize T4 late promoters, it is only capable of responding to the transcription-enhancing activity of the three replication proteins on acquiring an additional T4-specific modification.
Three-Dimensional Structure of Human Serum Albumin
Authors: Carter Daniel C. , He Xiao-Min , Munson Sibyl H. , Twigg Pamela D. , Gernert Kim M. , Broom M. Beth , Miller Teresa Y.
Published: October 2006

The three-dimensional structure of human serum albumin has been solved at 6.0 angstrom (Å) resolution by the method of multiple isomorphous replacement. Crystals were grown from solutions of polyethylene glycol in the infrequently observed space group
P
42
1
2 (unit cell constants
a
=
b
= 186.5 ± 0.5 Å and
c
= 81.0 ± 0.5 Å) and diffracted x-rays to lattice
d
-spacings of less than 2.9 A. The electron density maps are of high quality and revealed the structure as a predominantly α-helical globin protein in which the course of the polypeptide can be traced. The binding loci of several organic compounds have been determined.
Neuronal Correlates of Subjective Visual Perception
Authors: Logothetis Nikos K. , Schall Jeffrey D.
Published: October 2006

Neuronal activity in the superior temporal sulcus of monkeys, a cortical region that plays an important role in analyzing visual motion, was related to the subjective perception of movement during a visual task. Single neurons were recorded while monkeys (
Macaca mulatta
) discriminated the direction of motion of stimuli that could be seen moving in either of two directions during binocular rivalry. The activity of many neurons was dictated by the retinal stimulus. Other neurons, however, reflected the monkeys' reported perception of motion direction, indicating that these neurons in the superior temporal sulcus may mediate the perceptual experience of a moving object.
Molecular Genetics of Human Blue Cone Monochromacy
Authors: Nathans Jeremy , Davenport Carol M. , Maumenee Irene H. , Lewis Richard Alan , Hejtmancik J. Fielding , Litt Michael , Lovrien Everett , Weleber Richard , Bachynski Brian , Zwas Fred , Klingaman Roger , Fishman Gerald
Published: October 2006

Blue cone monochromacy is a rare X-linked disorder of color vision characterized by the absence of both red and green cone sensitivities. In 12 of 12 families carrying this trait, alterations are observed in the red and green visual pigment gene cluster. The alterations fall into two classes. One class arose from the wild type by a two-step pathway consisting of unequal homologous recombination and point mutation. The second class arose by nonhomologous deletion of genomic DNA adjacent to the red and green pigment gene cluster. These deletions define a 579-base pair region that is located 4 kilobases upstream of the red pigment gene and 43 kilobases upstream of the nearest green pigment gene; this 579-base pair region is essential for the activity of both pigment genes.
The Neostriatal Mosaic: Striatal Patch-Matrix Organization Is Related to Cortical Lamination
Authors: Gerfen Charles R.
Published: October 2006

The basal ganglia, of which the striatum is the major component, process inputs from virtually all cerebral cortical areas to affect motor, emotional, and cognitive behaviors. Insights into how these seemingly disparate functions may be integrated have emerged from studies that have demonstrated that the mammalian striatum is composed of two compartments arranged as a mosaic, the patches and the matrix, which differ in their neurochemical and neuroanatomical properties. In this study, projections from prefrontal, cingulate, and motor cortical areas to the striatal compartments were examined with the
Phaseolus vulgaris
-leucoagglutinin (PHA-L) anterograde axonal tracer in rats. Each cortical area projects to both the patches and the matrix of the striatum; however, deep layer V and layer VI corticostriatal neurons project principally to the patches, whereas superficial layer V and layer III and II corticostriatal neurons project principally to the matrix. The relative contribution of patch and matrix corticostriatal projections varies among the cortical areas examined such that allocortical areas provide a greater number of inputs to the patches than to the matrix, whereas the reverse obtains for neocortical areas. These results demonstrate that the compartmental organization of corticostriatal inputs is related to their laminar origin and secondarily to the cytoarchitectonic area of origin.
Release of Multiple Hormones by a Direct Action of Interleukin-1 on Pituitary Cells
Authors: Bernton Edward W. , Beach Judith E. , Holaday John W. , Smallridge Robert C. , Fein Henry G.
Published: October 2006

Exposure to bacterial endotoxins has long been known to stimulate the release of anterior pituitary hormones; administration of endotoxin was at one time a common clinical test of anterior pituitary function. Endotoxin is a potent stimulus for production of the endogenous pyrogenic protein, interleukin-1 (IL-1), by macrophages and monocytes. The possibility that IL-1 has a direct effect on the secretion of hormones by rat pituitary cells in a monolayer culture was investigated. Recombinant human IL-1β stimulated the secretion of adrenocorticotropic hormone, luteinizing hormone, growth hormone, and thyroid-stimulating hormone. Increased hormone secretion into culture supernatants was found with IL-1 concentrations ranging from 10
-9
M
to 10
-12
M
. Prolactin secretion by the monolayers was inhibited by similar doses. These concentrations of IL-1 are within the range reported for IL-1 in serum, suggesting that IL-1 generated peripherally by mononuclear immune cells may act directly on anterior pituitary cells to modulate hormone secretion in vivo. Incubation of IL-1 solutions with antibody to IL-1 neutralized these actions. These pituitary effects of IL-1 suggest that this monokine may be an important regulator of the metabolic adaptations to infectious stressors.
A Spatial-Temporal Model of Cell Activation
Authors: Alkon Daniel L. , Rasmussen Howard
Published: October 2006

A spatial-temporal model of calcium messenger function is proposed to account for sustained cellular responses to sustained stimuli, as well as for the persistent enhancement of cell responsiveness after removal of a stimulus, that is, cellular memory. According to this model, spatial separation of calcium function contributes to temporal separation of distinct phases of the cellular response. At different cellular sites, within successive temporal domains, the calcium messenger is generated by different mechanisms and has distinct molecular targets. In particular, prolonged cell activation is brought about by the interaction of calcium with another spatially confined messenger, diacylglycerol, to cause the association of protein kinase C with the plasma membrane. Activity of the membrane-associated protein kinase C is controlled by the rate of calcium cycling across the plasma membrane. In some instances, a single stimulus induces both protein kinase C activation and calcium cycling and thus causes prolonged activation; but in others, a close temporal association of distinct stimuli brings about cell activation via interaction of these intracellular messengers. Persistent enhancement of cell responsiveness after removal of stimuli is suggested to be due to the continued association, or anchoring, of protein kinase C to the membrane.
Insertional Mutagenesis of the
Drosophila
Genome with Single P Elements
Authors: Cooley Lynn , Kelley Richard , Spradling Allan
Published: October 2006

A versatile genetic method for identifying and cloning
Drosophila melanogaster
genes affecting any recognizable phenotype is described. Strains are constructed in which the insertion of a single P transposable element has caused a new mutation, greatly simplifying the genetic and molecular analysis of the affected gene. Mutagenesis is initiated by crossing two strains, each of which contains a specially designed P element. One element (jumpstarter), encoding P element transposase, efficiently mobilizes the second nonautonomous transposon (mutator), whose structure facilitates selection and cloning of new insertion mutations. Random mutator transpositions are captured in individual stocks that no longer contain jumpstarter, where they remain stable. This method was used to construct 1300 single P element insertion stocks which were then screened for recessive mutations. A library of single-element insertion strains will allow the structure and function of
Drosophila
genes to be readily correlated, and should have many other applications in
Drosophila
molecular genetics.
Estrogen-Dependent in Vitro Transcription from the Vitellogenin Promoter in Liver Nuclear Extracts
Authors: Corthésy Blaise , Hipskind Robert , Theulaz Irène , Wahli Walter
Published: October 2006

One approach to analyzing the molecular mechanisms of gene expression in vivo is to reconstitute these events in cell-free systems in vitro. Although there is some evidence for tissue-specific transcription in vitro, transcriptionally active extracts that mimic a steroid hormone-dependent enhancement of transcription have not been described. In the study reported here, nuclear extracts of liver from the frog
Xenopus laevis
were capable of estrogen-dependent induction of a homologous vitellogenin promoter that contained the estrogen-responsive element.
Activation of Cell-Specific Expression of Rat Growth Hormone and Prolactin Genes by a Common Transcription Factor
Authors: Nelson Christian , Albert Vivian R. , Elsholtz Harry P. , Lu Leslie I.-W. , Rosenfeld Michael G.
Published: October 2006

In the anterior pituitary gland, there are five phenotypically distinct cell types, including cells that produce either prolactin (lactotrophs) or growth hormone (somatotrophs). Multiple, related cis-active elements that exhibit synergistic interactions appear to be the critical determinants of the transcriptional activation of the rat prolactin and growth hormone genes. A common positive tissue-specific transcription factor, referred to as Pit-1, appears to bind to all the cell-specific elements in each gene and to be required for the activation of both the prolactin and growth hormone genes. The data suggest that, in the course of development, a single tissue-specific factor activates sets of genes that ultimately exhibit restricted cell-specific expression and define cellular phenotype.
Comparison of Biological Properties and Transforming Potential of Human PDGF-A and PDGF-B Chains
Authors: Beckmann M. Patricia , Betsholtz Christer , Heldin Carl-Henrik , Westermark Bengt , Di Marco Eddi , Di Fiore Pier Paolo , Robbins Keith C. , Aaronson Stuart A.
Published: October 2006

Human platelet-derived growth factor (PDGF) consists of two distinct but related polypeptide chains designated PDGF-A and PDGF-B. The gene encoding PDGF-B has given rise to the v-
sis
oncogene. In the present study the transforming activities of PDGF-A and PDGF-B genes are compared. The PDGF-A chain gene is markedly less efficient in inducing transformation than the PDGF-B gene under the influence of the same promoter. There are significant differences in the secretory and growth stimulating properties of the two chains. These properties appear to account for the much more potent transforming ability of the PDGF-B gene. These findings provide insights into biologic properties of a growth factor responsible for potent autocrine stimulation of abnormal cell proliferation.
Deficit of Spinal Cord Glycine/Strychnine Receptors in Inherited Myoclonus of Poll Hereford Calves
Authors: Gundlach Andrew L. , Dodd Peter R. , Grabara Corinne S. G. , Watson Wendy E. J. , Johnston Graham A. R. , Harper Peter A. W. , Dennis Julie A. , Healy Peter J.
Published: October 2006

Inherited myoclonus of Poll Hereford calves is characterized by hyperesthesia and myoclonic jerks of the skeletal musculature, which occur spontaneously and in response to sensory stimuli. The disease shows autosomal recessive inheritance, and significant proportions of the Poll Hereford herds in many countries are thought to be carriers of the mutant gene. Studies revealed a specific and marked (90 to 95 percent) deficit in [
3
H]strychnine binding sites in spinal cord membranes from myoclonic animals compared to controls, reflecting a loss of, or defect in, glycine/strychnine receptors. Spinal cord synaptosomes prepared from affected animals showed a significantly increased ability to accumulate [
3
H]glycine, indicating an increased capacity of the high-affinity neuronal uptake system for glycine. In contrast, stimulus-induced glycine release and spinal cord glycine concentrations were unaltered.
Control of Oscillations in Hematopoiesis
Authors: Kazarinoff Nicholas D. , van denDriessche Pauline
Published: October 2006

Results of a mathematical analysis of models of hematopoietic systems introduced by Mackey and Glass are given. The models include a constant time lag, and it is shown that this lag has a critical value above which oscillations in blood cell concentration occur. To reduce the likelihood of disease associated with such oscillations, physiologists should seek to learn how to increase this critical value of the lag.
Patterns of Growth Hormone-Eeleasing Factor and Somatostatin Secretion into the Hypophysial-Portal Circulation of the Rat
Authors: Plotsky Paul M. , Vale Wylie
Published: October 2006

The interrelation between the secretion of two hypophysiotropic peptides, growth hormone-releasing factor (GRF) and somatostatin (SRIF), in the generation of episodic growth hormone (GH) secretion was inferred from direct measurements of immunoreactive GRF and immunoreactive SRIF concentrations in the hypophysial-portal plasma of the rat. Secretion of immunoreactive GRF was found to be episodic, with maximal concentrations present during periods of expected GH secretory episodes. Secretion of immunoreactive GRF was accompanied by a moderate reduction in portal plasma levels of immunoreactive SRIF. Passive immunoneutralization of SRIF was associated with increased concentrations of immunoreactive GRF in hypophysial-portal plasma. On the basis of these observations, it appears that each GH secretory episode is initiated by pulsatile secretion of immunoreactive GRF into the portal circulation, which is preceded by or is concurrent with a moderate reduction of inhibitory tone provided by portal immunoreactive SRIF. These experiments provide direct insights into central and adenohypophysial mechanisms by which GRF and SRIF interact to generate episodic secretion of GH.
Decreased Hippocampal Inhibition and a Selective Loss of Interneurons in Experimental Epilepsy
Authors: Sloviter Robert S.
Published: October 2006

The occurrence of seizure activity in human temporal lobe epilepsy or status epilepticus is often associated with a characteristic pattern of cell loss in the hippocampus. An experimental model that replicates this pattern of damage in normal animals by electrical stimulation of the afferent pathway to the hippocampus was developed to study changes in structure and function that occur as a result of repetitive seizures. Hippocampal granule cell seizure activity caused a persistent loss of recurrent inhibition and irreversibly damaged adjacent interneurons. Immunocytochemical staining revealed unexpectedly that γ-aminobutyric acid (GABA)-containing neurons, thought to mediate inhibition in this region and predicted to be damaged by seizures, had survived. In contrast, there was a nearly complete loss of adjacent somatostatin-containing interneurons and mossy cells that may normally activate inhibitory neurons. These results suggest that the seizure-induced loss of a basket cell-activating system, rather than a loss of inhibitory basket cells themselves, may cause disinhibition and thereby play a role in the pathophysiology and pathology of the epileptic state.
Structural Evidence for the Authenticity of the Human Retinoblastoma Gene
Authors: Fung Yuen-Kai T. , Murphree A. Linn , T'Ang Anne , Qian Jin , Hinrichs Steven H. , Benedict William F.
Published: October 2006

The retinoblastoma (Rb) gene is the prototype for a class of recessive human cancer genes in which loss of activity of both normal alleles is thought to be associated with tumorigenesis. Sixteen of 40 retinoblastomas examined with a complementary DNA probe shown to be the Rb gene had identifiable structural changes of the Rb gene including in some cases homozygous internal deletions with corresponding truncated transcripts. An osteosarcoma also had a homozygous internal deletion with a truncated transcript. In addition, possible hot spots for deletion were identified within the Rb genomic locus. Among those tumors with no identifiable structural changes there was either absence of an Rb transcript or abnormal expression of the Rb transcript. Comparison of the structural changes in the tumor cells and fibroblasts of certain patients provided support for Knudson's two-hit hypothesis for the development of retinoblastoma at the molecular level. The ability to detect germline structural deletions in fibroblasts from some patients with bilateral retinoblastoma also indicates that the isolated gene is useful for diagnostic purposes.