bluuebunny/crossref_metadata_2025 huggingface dataset:
A Mercury-Catalyzed, High-Yield System for the Oxidation of Methane to Methanol
Authors: Periana Roy A. , Taube Douglas J. , Evitt Eric R. , Löffler Daniel G. , Wentrcek Paul R. , Voss George , Masuda Toshihiko
Published: October 2006

A homogeneous system for the selective, catalytic oxidation of methane to methanol via methyl bisulfate is reported. The net reaction catalyzed by mercuric ions, Hg(II), is the oxidation of methane by concentrated sulfuric acid to produce methyl bisulfate, water, and sulfur dioxide. The reaction is efficient. At a methane conversion of 50 percent, 85 percent selectivity to methyl bisulfate (∼43 percent yield; the major side product is carbon dioxide) was achieved at a molar productivity of 10–7mole per cubic centimeter per second and Hg(II) turnover frequency of 10–3per second. Separate hydrolysis of methyl bisulfate and reoxidation of the sulfur dioxide with air provides a potentially practical scheme for the oxidation of methane to methanol with molecular oxygen. The primary steps of the Hg(II)-catalyzed reaction were individually examined and the essential elements of the mechanism were identified. The Hg(II) ion reacts with methane by an electrophilic displacement mechanism to produce an observable species, CH3HgOSO3H, 1. Under the reaction conditions, 1 readily decomposes to CH3OSO3H and the reduced mercurous species, Hg22+. The catalytic cycle is completed by the reoxidation of Hg22+with H2SO4to regenerate Hg(II) and byproducts SO2and H2O. Thallium(III), palladium(II), and the cations of platinum and gold also oxidize methane to methyl bisulfate in sulfuric acid.
Simple Systems That Exhibit Self-Directed Replication
Authors: Reggia James A. , Armentrout Steven L. , Chou Hui-Hsien , Peng Yun
Published: October 2006

Biological experience and intuition suggest that self-replication is an inherently complex phenomenon, and early cellular automata models support that conception. More recently, simpler computational models of self-directed replication called sheathed loops have been developed. It is shown here that "unsheathing" these structures and altering certain assumptions about the symmetry of their components leads to a family of nontrivial self-replicating structures, some substantially smaller and simpler than those previously reported. The dependence of replication time and transition function complexity on initial structure size, cell state symmetry, and neighborhood are examined. These results support the view that self-replication is not an inherently complex phenomenon but rather an emergent property arising from local interactions in systems that can be much simpler than is generally believed.
Stable Compounds of Helium and Neon: He@C
60
and Ne@C
60
Authors: Saunders Martin , Jiménez-Vázquez Hugo A. , Cross R. James , Poreda Robert J.
Published: October 2006

It is demonstrated that fullerenes, prepared via the standard method (an arc between graphite electrodes in a partial pressure of helium), on heating to high temperatures release
4
He and
3
He. The amount corresponds to one
4
He for every 880,000 fullerene molecules. The
3
He/
4
He isotopic ratio is that of tank helium rather than that of atmospheric helium. These results convincingly show that the helium is inside and that there is no exchange with the atmosphere. The amount found corresponds with a prediction from a simple model based on the expected volume of the cavity. In addition, the temperature dependence for the release of helium implies a barrier about 80 kilocalories per mole. This is much lower than the barrier expected from theory for helium passing through one of the rings in the intact structure. A mechanism involving reversibly breaking one or more bonds to temporarily open a "window" in the cage is proposed. A predicted consequence of this mechanism is the incorporation of other gases while the "window" is open. This was demonstrated through the incorporation of
3
He and neon by heating fullerene in their presence.
Fossilization of Soft Tissue in the Laboratory
Authors: Briggs Derek E. G. , Kear Amanda J.
Published: October 2006

Some of the most remarkable fossils preserve cellular details of soft tissues. In many of these, the tissues have been replaced by calcium phosphate. This process has been assumed to require elevated concentrations of phosphate in sediment pore waters. In decay experiments modern shrimps became partially mineralized in amorphous calcium phosphate, preserving cellular details of muscle tissue, particularly in a system closed to oxygen. The source for the formation of calcium phosphate was the shrimp itself. Mineralization, which was accompanied by a drop in pH, commenced within 2 weeks and increased in extent for at least 4 to 8 weeks. This mechanism halts the normal loss of detail of soft-tissue morphology before fossilization. Similar closed conditions would prevail where organisms are rapidly overgrown by microbial mats.
Cyclocarbon Coalescence: Mechanisms for Tailor-Made Fullerene Formation
Authors: McElvany Stephen W. , Ross Mark M. , Goroff Nancy S. , Diederich François
Published: October 2006

The availability of macroscopic quantities of fullerenes has resulted in a vast number of physical and chemical studies of these new materials. However, the mechanisms that lead to the formation of these spherical carbon allotropes are not well understood. Mass spectral evidence has been obtained for the size-selective growth of fullerenes through the coalescence of cyclo[
n
]carbons, molecular carbon allotropes consisting of monocyclic rings with
n
carbon atoms. Whereas coalescence of cyclo[30]carbon (
cyclo
-C
30
) produces predominantly buckminsterfullerene (C
60
), the smaller rings
cyclo
-C
18
and
cyclo
-C
24
preferentially produce fullerene C
70
through distinct intermediates. The present studies not only provide new insights into fullerene formation mechanisms but also raise the possibility of tailoring the size distributions of fullerenes by variation of the appropriate properties of the precursors.
Boundary Layer Profiles in Plasma Chemical Vapor Deposition
Authors: Green David S. , Owano Thomas G. , Williams Skip , Goodwin David G. , Zare Richard N. , Kruger Charles H.
Published: October 2006

A nonlinear optical spectroscopy based on degenerate four-wave mixing has made possible direct measurements of species temperature and concentration profiles through the boundary layer of a reactive plasma at atmospheric pressure. Spectra were obtained for CH and C
2
radicals over a range of conditions including those for the plasma chemical vapor deposition of diamond films. Numerical simulations based on a one-dimensional stagnation-point flow model are in good agreement with the measurements. The CH mole fraction is shown to rise and fall as a function of distance from the substrate, which is compelling experimental evidence for the complex chemistry that is occurring in the plasma boundary layer.
Cryptic Grain-Scale Heterogeneity of Oxygen Isotope Ratios in Metamorphic Magnetite
Authors: Valley John W. , Graham Colin M.
Published: October 2006

Oxygen isotope ratios measured by ion microprobe in magnetite from granulite-facies marble of the Adirondack Mountains, New York, range from +2 to +11 per mil (standard mean ocean water) across a single grain that measures 3 millimeters by 5 millimeters. Low values are concentrated in irregular domains near the grain boundary but also occur in the grain's interior. In contrast, grains 1 millimeter in diameter that are from a second nearby sample show no significant heterogeneity, except within 10 micrometers of the grain boundary. These data, including large gradients of up to 9 per mil per 10 micrometers, provide important new constraints on the nature and origins of intragrain isotopic heterogeneity and on oxygen isotope thermometry. The differences between these magnetite grains result from contrasting mechanisms of isotope exchange with fluids after the peak of regional metamorphism. Volume diffusion of oxygen through the crystal structure of magnetite contributed to isotope exchange in the rims of small grains, but larger grains are crosscut by healed cracks that are not readily detected and that short-circuited diffusion.
A Nickel Metal Hydride Battery for Electric Vehicles
Authors: Ovshinsky S. R. , Fetcenko M. A. , Ross J.
Published: October 2006

Widespread use of electric vehicles can have significant impact on urban air quality, national energy independence, and international balance of trade. An efficient battery is the key technological element to the development of practical electric vehicles. The science and technology of a nickel metal hydride battery, which stores hydrogen in the solid hydride phase and has high energy density, high power, long life, tolerance to abuse, a wide range of operating temperature, quick-charge capability, and totally sealed maintenance-free operation, is described. A broad range of multi-element metal hydride materials that use structural and compositional disorder on several scales of length has been engineered for use as the negative electrode in this battery. The battery operates at ambient temperature, is made of nontoxic materials, and is recyclable. Demonstration of the manufacturing technology has been achieved.
Frequency-Dependent Natural Selection in the Handedness of Scale-Eating Cichlid Fish
Authors: Hori Michio
Published: October 2006

Frequency-dependent natural selection has been cited as a mechanism for maintaining polymorphisms in biological populations, although the process has not been documented conclusively in field study. Here, it is demonstrated that the direction of mouth-opening (either left-handed or right-handed) in scale-eating cichlid fish of Lake Tanganyika is determined on the basis of simple genetics and that the abundance of individuals with left- or right-handedness depends on frequency-dependent natural selection. Attacking from behind, right-handed individuals snatched scales from the prey's left flank and left-handed ones from the right flank. Within a given population, the frequency of the two phenotypes oscillated around unity. This phenomenon was effected through frequency-dependent selection exerted by the prey's alertness. Thus, individuals of the rare phenotype had more success as predators than those of the more common phenotype.
Identification of a Sex Pheromone from a Spider
Authors: Schulz S. , Toft S.
Published: October 2006

The compounds (
R
)-3-hydroxybutyric acid and its dimer, (
R
)-3-[(
R
)-3-hydroxybutyryloxy]-butyric acid, have been identified as sex pheromones of a spider. These compounds elicit web reduction behavior by males of
Linyphia triangularis
(Clerck) on the webs of unmated adult females.
Tough Times at La Brea: Tooth Breakage in Large Carnivores of the Late Pleistocene
Authors: VanValkenburgh Blaire , Hertel Fritz
Published: October 2006

One million to two million years ago, most of today's large, predatory mammals coexisted with larger extinct species, such as saber-toothed cats and giant running bears. Comparisons of tooth fracture frequencies from modern and Pleistocene carnivores imply that predator-prey dynamics and interspecific interactions must have been substantially different 36,000 to 10,000 years ago. Tooth fracture frequencies of four Rancho La Brea species—dire wolf, coyote, saber-toothed cat, and American lion—were about three times that of extant carnivores. Consequently, these findings suggest that these species utilized carcasses more fully and likely competed more intensely for food than present-day large carnivores.
High-Density Nanosecond Charge Trapping in Thin Films of the Photoconductor ZnODEP
Authors: Liu Chong-yang , Pan Horng-long , Fox Marye Anne , Bard Allen J.
Published: October 2006

An electrooptical memory effect is observed with solid thin films of the photoconductor zinc-octakis(β-decoxyethyl) porphyrin (ZnODEP) sandwiched between two optically transparent electrodes. Upon irradiation with the simultaneous application of an electric field, electron-hole pairs are generated and separated within the photoconductive layer. These electron-hole pairs become "frozen" within the films when the irradiation is interrupted. These trapped charges can be released by irradiation of the cell, resulting in a transient short-circuit photocurrent. No cross talk between adjacent memory elements separated by ∼0.2 micrometer (a density of 3 gigabits per square centimeter) was detected. The charge storage system is robust and nonvolatile. The response time for the write-read beam is in the subnanosecond range, and no refreshing is required for long-term retention of trapped charges.
The Seasonal Evolution of Reactive Chlorine in the Northern Hemisphere Stratosphere
Authors: Toohey D. W. , Avallone L. M. , Lait L. R. , Newman P. A. , Schoeberl M. R. , Fahey D. W. , Woodbridge E. L. , Anderson J. G.
Published: October 2006

In situ measurements of chlorine monoxide (ClO) at mid- and high northern latitudes are reported for the period October 1991 to February 1992. As early as mid-December and throughout the winter, significant enhancements of this ozone-destroying radical were observed within the polar vortex shortly after temperatures dropped below 195 k. Decreases in ClO observed in February were consistent with the rapid formation of chlorine nitrate (ClONO
2
) by recombination of ClO with nitrogen dioxide (NO
2
) released photochemically from nitric acid (HNO
3
). Outside the vortex, ClO abundances were higher than in previous years as a result of NO

x

suppression by heterogeneous reactions on sulfate aerosols enhanced by the eruption of Mount Pinatubo.
Inclined-Field Structure, Morphology, and Pinning of the Vortex Lattice in Microtwinned YBa
2
Cu
3
O
7
Authors: Keimer B. , Doğan F. , Aksay I. A. , Erwin R. W. , Lynn J. W. , Sarikaya M.
Published: October 2006

A detailed small-angle neutron scattering study of the vortex lattice in a single crystal of YBa
2
Cu
3
O
7
was made for a field of 0.5 tesla inclined at angles between 0 and 80 degrees to the crystalline
c
axis. The vortex lattice is triangular for all angles, and for angles less than or equal to 70 degrees its orientation adjusts itself to maximize the pinning energy to densely and highly regularly spaced twin planes. These observations have important implications for the microscopic flux-pinning mechanism, and hence for the critical current achievable in YBa
2
Cu
3
O
7
. For large angles (about 80 degrees) the vortex lattice consists of independent chains in the orientation predicted by anisotropic London theory.
A Spatially Resolved X-ray Image of a Star Like the Sun
Authors: Schmitt J. H. M. M. , Kürster M.
Published: October 2006

Observations made with the x-ray satellite ROSAT (Roentgen Satellite) have produced the first spatially resolved x-ray image of a corona around a star like our sun. The star is the secondary in the eclipsing binary system α Coronae Borealis (CrB), which consists of one star of spectral type A0V and one of type G5V. The x-ray light curve of α CrB shows a total x-ray eclipse during secondary optical minimum, with the G star behind the A star. The totality of the eclipse demonstrates that the A-type component in α CrB is x-ray dark and that the x-ray flux arises exclusively from the later-type companion. The x-ray eclipse ingress and egress are highly asymmetric compared with the optical eclipse, indicating a highly asymmetric x-ray intensity distribution on the surface of the G star. From a detailed modeling of the ingress and egress of the x-ray light curve, an eclipse map of the G star was constructed by a method based on an optimization by simulated annealing.
X-ray Linear Dichroism Microscopy
Authors: Ade H. , Hsiao B.
Published: October 2006

Chemical-specific x-ray linear dichroism was observed in an x-ray microscope as evidenced by changes in relative contrast upon azimuthal rotation of the sample. As a demonstration, thin sections of a partially ordered polymer fiber were examined with a transmission x-ray microscope near the carbon
K
-shell absorption edge to provide chemical-specific imaging at 50-nanometer spatial resolution. The observed dichroism and change in contrast upon rotation arise from the polarization dependence of the near-edge x-ray absorption cross section and can be used to image the orientation of specific chemical bonds.
Stable Isotope Enrichment in Paleowaters of the Southeast Atlantic Coastal Plain, United States
Authors: Plummer L. Niel
Published: October 2006

Paleowaters from the Floridan aquifer system in the southeastern Atlantic coastal plain have higher D/H and
18
O/
16
O ratios than local Holocene ground water. Maximum δ
18
O enrichments in ground water having adjusted radiocarbon ages of 20,000 to 26,000 years are 0.7 to 2.3 per mil. The trend in isotopic enrichment in paleowaters is the reverse of that normally observed in continental glacial age ground water. Dissolved nitrogen and argon concentrations indicate, however, that the average recharge temperature was 5.3°C cooler than that today. The data indicate cool conditions in the southeast Atlantic coastal plain during the last glacial maximum, with recharge limited primarily to late summer tropical cyclones and hurricanes.
Mantle Plume Helium in Submarine Basalts from the Galápagos Platform
Authors: Graham D. W. , Christie D. M. , Harpp K. S. , Lupton J. E.
Published: October 2006

Helium-3/helium-4 ratios in submarine basalt glasses from the Galápagos Archipelago range up to 23 times the atmospheric ratio in the west and southwest. These results indicate the presence of a relatively undegassed mantle plume at the Galápagos hot spot and place Galápagos alongside Hawaii, Iceland, and Samoa as the only localities known to have such high helium-3/helium-4 ratios. Lower ratios across the rest of the Galápagos Archipelago reflect systematic variations in the degree of dilution of the plume by entrainment of depleted material from the asthenosphere. These spatial variations reveal the dynamics of the underlying mantle plume and its interaction with the nearby Galápagos Spreading Center.
Hydrogen Tunneling in Enzyme Reactions
Authors: Cha Yuan , Murray Christopher J. , Klinman Judith P.
Published: October 2006

Primary and secondary protium-to-tritium (H/T) and deuterium-to-tritium (D/T) kinetic isotope effects for the catalytic oxidation of benzyl alcohol to benzaldehyde by yeast alcohol dehydrogenase (YADH) at 25 degrees Celsius have been determined. Previous studies showed that this reaction is nearly or fully rate limited by the hydrogen-transfer step. Semiclassical mass considerations that do not include tunneling effects would predict that
k
H
/
k
T
= (
k
D
/
k
T
)3.26, where
k
H
,
k
D
, and
k
T
are the rate constants for the reaction of protium, deuterium, and tritium derivatives, respectively. Significant deviations from this relation have now been observed for both primary and especially secondary effects, such that experimental H/T ratios are much greater than those calculated from the above expression. These deviations also hold in the temperature range from 0 to 40 degrees Celsius. Such deviations were previously predicted to result from a reaction coordinate containing a significant contribution from hydrogen tunneling.
The Neutrophil-Activating Protein (NAP-1) Is Also Chemotactic for T Lymphocytes
Authors: Larsen Christian Grønhøj , Anderson Arthur O. , Appella Ettore , Oppenheim Joost J. , Matsushima Kouji
Published: October 2006

T lymphocyte chemotactic factor (TCF) was purified to homogeneity from the conditioned media of phytohemagglutinin-stimulated human blood mononuclear leukocytes by a sequence of chromatography procedures. The amino-terminal amino acid sequence of the purified TCF showed identity with neutrophil-activating protein (NAP-1). Both TCF and recombinant NAP-1 (rNAP-1) were chemotactic for neutrophils and T lymphocytes in vitro supporting the identity of TCF with NAP-1. Injection of rNAP-1 into lymphatic drainage areas of lymph nodes in Fisher rats caused accelerated emigration of only lymphocytes in high endothelial venules. Intradermal injection of rNAP-1 caused dose-dependent accumulation of neutrophils and lymphocytes.
The Role of Somatic Hypermutation in the Generation of Antibody Diversity
Authors: French Deborah L. , Laskov Reuven , Scharff Matthew D.
Published: October 2006

The immune system is capable of establishing an enormous repertoire of antibodies before its first contact with antigen. Most antibodies that express germ-line sequences are of relatively low affinity. Once antigen enters the system, it stimulates a somatic mutational mechanism that generates antibodies of higher affinity and selects for the expression of those antibodies to produce a more effective immune response. The details of the mechanism and regulation of somatic hypermutation remain to be elucidated.
Translational Blockade Imposed by Cytokine-Derived UA-Rich Sequences
Authors: Kruys Véronique , Marinx Olivier , Shaw Gray , Deschamps Jacqueline , Huez George
Published: October 2006

The messenger RNAs specifying certain proteins involved in the inflammatory response and certain oncoproteins contain a conserved UA-rich sequence in the 3′ untranslated region. This sequence, which is composed of several interspersed repeats of the octanucleotide UUAUUUAU, has been shown to destabilize mRNA in some eukaryotes. However, this effect is not seen when mRNAs are transferred to
Xenopus
oocytes, which made it possible to separate stability from translational regulation. For interferon, granulocyte-macrophage colony-stimulating factor, and c-
fos
RNAs, the UA-rich sequence was observed to preclude mRNA translation.
Visuomotor Coordination in Reaching and Locomotion
Authors: Georgopoulos A. P. , Grillner S.
Published: October 2006

Locomotion and reaching have traditionally been regarded as separate motor activities. In fact, they may be closely connected both from an evolutionary and a neurophysiological viewpoint. Reaching seems to have evolved from the neural systems responsible for the active and precise positioning of the limb during locomotion; moreover, it seems to be organized in the spinal cord. The motor cortex and its corticospinal outflow are preferentially engaged when precise positioning of the limb is needed during locomotion and are also involved during reaching and active positioning of the hand near objects of interest. All of these motor activities require visuomotor coordination, and it is this coordination that could be achieved by the motor cortex and interconnected parietal and cerebellar areas.
Mitosis
Authors: McIntosh J. Richard , Koonce Michael P.
Published: October 2006

Data that describe both the structure and the physiology of the mitotic spindle are reviewed. Some of the molecules that have been shown to play a role in mitosis are tabulated, and how mitosis might work is considered.
Scissors-Grip Model for DNA Recognition by a Family of Leucine Zipper Proteins
Authors: Vinson Charles R. , Sigler Paul B. , McKnight Steven L.
Published: October 2006

C/EBP is a sequence-specific DNA binding protein that regulates gene expression in certain mammalian cells. The region of the C/EBP polypeptide required for specific recognition of DNA is related in amino acid sequence to other regulatory proteins, including the Fos and Jun transforming proteins. It has been proposed that these proteins bind DNA via a bipartite structural motif, consisting of a dimerization interface termed the "leucine zipper" and a DNA contact surface termed the "basic region." An evaluation of the properties of conserved amino acids within the basic region of 11 deduced protein sequences, coupled with the observation that they are located at an invariant distance from the leucine zipper, has led to the formulation of a "scissors-grip" model for DNA binding. The architectural features of this model are well suited for interaction with directly abutted, dyadsymmetric DNA sequences. Data supportive of the model were obtained with chemical probes of protein: DNA complexes.
BAS1 Has a Myb Motif and Activates
HIS4
Transcription Only in Combination with BAS2
Authors: Tice-Baldwin Kimberly , Fink Gerald R. , Arndt Kim T.
Published: October 2006

The BAS1 and BAS2 proteins are both required for activation of GCN4-independent (basal)
HIS4
transcription in yeast. BAS1 has an NH
2
-terminal region similar to those of the
myb
proto-oncogene family. BAS1 and BAS2, which contains a homeo box, bound to adjacent sites on the
HIS4
promoter. The joint requirement of BAS1 and BAS2 for activation is probably not due to cooperative binding or the transcriptional control of one of the genes by the other. Although BAS1 and BAS2 were both required for activation of
HIS4
transcription, BAS1 was not required for BAS2-dependent expression of the secreted acid phosphatases. The transcriptional activators of
HIS4
have DNA binding domains that are conserved in evolution (BAS1 = Myb, BAS2 = homeo box, GCN4 = Jun). Their interactions, therefore, may be relevant to the control of gene expression in more complex systems.
Bacterial Blight of Soybean: Regulation of a Pathogen Gene Determining Host Cultivar Specificity
Authors: Huynh Thanh V. , Dahlbeck Douglas , Staskawicz Brain J.
Published: October 2006

Soybean cultivars resistant to
Pseudomonas syringae
pathovar
glycinea
(
Psg
), the causal agent of bacterial blight, exhibit a hypersensitive (necrosis) reaction (HR) to infection.
Psg
strains carrying the
avrB
gene elicit the HR in soybean cultivars carrying the resistance gene
Rpg1
.
Psg
expressing
avrB
at a high level and capable of eliciting the HR in the absence of de novo bacterial RNA synthesis have been obtained in in vitro culture. Nutritional signals and regions within the
Psg
hrp
gene cluster, an approximately 20-kilobase genomic region also necessary for pathogenicity, control
avrB
transcription.
Corticosteroid Modulation of Hippocampal Potentials: Increased Effect with Aging
Authors: Kerr D. Steven , Campbell Lee W. , Hao Su-Yang , Landfield Philip W.
Published: October 2006

Adrenal steroids bind specifically to hippocampal neurons under normal conditions and may contribute to hippocampal cell loss during aging, but little is known about the neurophysiological mechanisms by which they may change hippocampal cell function. In the present studies, adrenal steroids have been shown to modulate a well-defined membrane conductance in hippocampal pyramidal cells. The calcium-dependent slow afterhyperpolarization is reduced in hippocampal slices from adrenalectomized rats, and it is increased after in vivo or in vitro administration of the adrenal steroid, corticosterone. Calcium action potentials are also reduced in adrenalectomized animals, indicating that the primary effect of corticosteroids may be on calcium conductance. The afterhyperpolarization component reduced by adrenalectomy is greater in aged rats than in young rats, suggesting that, with aging, there is an increased effect of corticosteroids on some calcium-mediated brain processes. Because elevated concentrations of intracellular calcium can be cytotoxic, these observations may increase the understanding of glucocorticoid involvement in brain aging as well as of the normal functions of these steroids in the brain.
The Gene for Enhancer Binding Proteins E12/E47 Lies at the t(1;19) Breakpoint in Acute Leukemias
Authors: Mellentin Julia D. , Murre Cornelis , Donlon Timothy A. , McCaw Patrick S. , Smith Stephen D. , Carroll Andrew J. , McDonald Marcy E. , Baltimore David , Cleary Michael L.
Published: October 2006

The gene (
E2A
) that codes for proteins with the properties of immunoglobulin enhancer binding factors E12/E47 was mapped to chromosome region 19p13.2-p13.3, a site associated with nonrandom translocations in acute lymphoblastic leukemias. The majority of t(1;19)(q23;p13)-carrying leukemias and cell lines studied contained rearrangements of
E2A
as determined by DNA blot analyses. The rearrangements altered the
E2A
transcriptional unit, resulting in the synthesis of a transcript larger than the normal-sized
E2A
mRNAs in one of the cell lines with this translocation. These observations indicate that the gene for a transcription factor is located at the breakpoint of a consistently recurring chromosomal translocation in many acute leukemias and suggest a direct role for alteration of such factors in the pathogenesis of some malignancies.
Unwinding of Duplex DNA from the SV40 Origin of Replication by T Antigen
Authors: Dodson Mark , Dean Frank B. , Bullock Peter , Echols Harrison , Hurwitz Jerard
Published: October 2006

The T antigen specified by SV40 virus is the only viral-encoded protein required for replication of SV40 DNA. T antigen has two activities that appear to be essential for viral DNA replication: specific binding to duplex DNA at the origin of replication and helicase activity that unwinds the two DNA strands. As judged by electron microscopy, DNA unwinding is initiated at the origin of replication and proceeds bidirectionally. Either linear or circular DNA molecules containing the origin of replication are effective substrates; with closed circular DNA, a topoisomerase capable of removing positive superhelical turns is required for an efficient reaction. Presence of an origin sequence on duplex DNA and a single-strand DNA-binding protein appear to be the only requirements for T antigen to catalyze unwinding. This reaction mediated by T antigen defines a likely pathway to precise initiation of DNA replication: (i) the sequence-specific binding activity locates the origin sequence, (ii) the duplex DNA is unwound at this site, and (iii) the DNA polymerase and primase begin DNA replication. A similar pathway has been inferred for the localized initiation of DNA replication by bacteriophage λ and by
Escherichia coli
in which a sequence-specific binding protein locates the origin and directs the DnaB helicase to this site. Observations with the SV40 system indicate that localized initiation of duplex DNA replication may be similar for prokaryotes and eukaryotes.
Exon-Intron Organization in Genes of Earthworm and Vertebrate Globins
Authors: Jhiang Sissy M. , Garey James R. , Riggs Austen F.
Published: October 2006

The structure of an invertebrate, intron-containing globin gene has been determined as part of a study of the evolution of hemoglobin. The gene encoding chain
c
of
Lumbricus terrestris
hemoglobin has the two-intron, three-exon structure characteristic of vertebrate globin genes, and the exact positions of the splice junctions are conserved. The two introns interrupting the coding sequence are longer than those of known hemoglobins but shorter than myoglobin introns. The gene encodes a secretory preglobin containing a 16-residue signal peptide, as expected for an extracellular hemoglobin. However, no intron separates the DNA encoding the signal sequence from that of the globin sequence. The 3′ untranslated region of the
Lumbricus
gene is much longer than those of the genes for other hemoglobins and is similar to those found for myoglobins.
Guanosine Triphosphatase Activating Protein (GAP) Interacts with the p21
ras
Effector Binding Domain
Authors: Adari Hedy , Lowy Douglas R. , Willumsen Berthe M. , Der Channing J. , McCormick Frank
Published: October 2006

A cytoplasmic protein that greatly enhances the guanosine triphosphatase (GTPase) activity of N-
ras
protein but does not affect the activity of oncogenic
ras
mutants has been recently described. This protein (GAP) is shown here to be ubiquitous in higher eukaryotes and to interact with H-
ras
as well as with N-
ras
proteins. To identify the region of
ras
p21 with which GAP interacts, 21 H-
ras
mutant proteins were purified and tested for their ability to undergo stimulation of GTPase activity by GAP. Mutations in nonessential regions of H-
ras
p21 as well as mutations in its carboxyl-terminal domain (residues 165-185) and purine binding region (residues 117 and 119) did not decrease the ability of the protein to respond to GAP. In addition, an antibody against the carboxyl-terminal domain did not block GAP activity, supporting the conclusion that GAP does not interact with this region. Transforming mutations at positions 12, 59, and 61 (the phosphoryl binding region) abolished GTPase stimulation by GAP. Point mutations in the putative effector region of
ras
p21 (amino acids 35, 36, and 38) were also insensitive to GAP. However, a point mutation at position 39, shown previously not to impair effector function, did not alter GAP-p21 interaction. These results indicate that GAP interaction may be essential for
ras
p21 biological activity and that it may be a
ras
effector protein.
Two Classes of PDGF Receptor Eecognize Different Isoforms of PDGF
Authors: Hart Charles E. , Forstrom John W. , Kelly James D. , Seifert Ronald A. , Smith Robert A. , Ross Russell , Murray Mark J. , Bowen-Pope Daniel F.
Published: October 2006

Previous studies involving platelet-derived growth factor (PDGF) have been based on the premise that a single cell-surface receptor binds all three isoforms of PDGF (AA, BB, and AB). It is now shown that two populations of PDGF receptor exist and can be distinguished by their ligand binding specificity. The B receptor binds only the BB dimer, whereas the A/B receptor binds AA, BB, and AB dimers. Human dermal fibroblasts appear to express seven times as much B receptor as A/B receptor. The B receptor is responsible for most PDGF receptor phosphorylation.
Poliovirus Host Range Is Determined by a Short Amino Acid Sequence in Neutralization Antigenic Site I
Authors: Murray Michael G. , Bradley Jonathan , Yang Xiao-Feng , Wimmer Eckard , Moss Eric G. , Racaniello Vincent R.
Published: October 2006

The mouse-adapted strain of poliovirus type 2 (Lansing) induces fatal poliomyelitis in mice after intracerebral inoculation, whereas mice inoculated with poliovirus type 1 (Mahoney) show no signs of disease. Previous work indicated that the adaptation to mouse virulence is associated with the viral capsid proteins and that mutations in neutralization antigenic site I of poliovirus reduce neurovirulence of the Lansing strain in mice. The role of antigenic site I in mouse neurovirulence was further explored by constructing an antigenic hybrid virus. Six amino acids in antigenic site I of the Mahoney strain were replaced with a sequence specific for the Lansing strain by using a mutagenesis cartridge. The hybrid virus was neutralized by polyclonal antisera elicited by the type 1 and type 2 strains of poliovirus and by neutralizing monoclonal antibodies directed against antigenic site I of type 2 virus. The hybrid virus induced paralytic disease in mice, an observation demonstrating that a short sequence of amino acids in antigenic site I is an important determinant of poliovirus host range. Antigenic site I may be involved in attachment of poliovirus to cells of the mouse central nervous system.
Two Mechanisms for the Extinction of Gene Expression in Hybrid Cells
Authors: Tripputi Pasquale , Guérin Sylvain L. , Moore David D.
Published: October 2006

When two different mammalian cell types are fused to generate a stable hybrid cell line, genes that are active in only one of the parents are frequently shut off, a phenomenon called extinction. In this study two distinct, complementary mechanisms for such extinction of growth hormone gene expression were identified. In hybrids formed by fusing fibroblasts to pituitary cells, pituitary-specific proteins that bind to the growth hormone promoter were absent. In addition, a negative regulatory element located near the rat growth hormone promoter was specifically activated.
The S1-sensitive Form of D(C-T)

n

⋅d(A-G)

n

: Chemical Evidence for a Three-Stranded Structure in Plasmids
Authors: Johnston Brian H.
Published: October 2006

Homopurine-homopyrimidine sequences that flank certain actively transcribed genes are hypersensitive to single strand-specific nucleases such as S1. This has raised the possibility that an unusual structure exists in these regions that might be involved in recognition or regulation. Several of these sequences, including d(C-T)

n

⋅d(A-G)

n

, are known to undergo a transition in plasmids to an underwound state that is hypersensitive to single strand-specific nucleases; this transition occurs under conditions of moderately acid
p
H and negative supercoiling. Chemical probes were used to examine the reactivity of a restriction fragment from a human U1 gene containing the sequence d(C-T)
18
⋅d(A-G)
18
as a function of supercoiling and
p
H, and thus analyze the structure in this region. Hyperreactivity was seen in the center and at one end of the (C-T)

n

tract, and continuously from the center to the same end of the (A-G)

n

tract, in the presence of supercoiling and
p
H ≤ 6.0. These results provide strong support for a triple-helical model recently proposed for these sequences and are inconsistent with other proposed structures.
Muscarinic Depression of Long-Term Potentiation in CA3 Hippocampal Neurons
Authors: Williams Stephen , Johnston Daniel
Published: October 2006

Behavioral studies have suggested that muscarinic cholinergic systems have an important role in learning and memory. A muscarinic cholinergic agonist is now shown to affect synaptic plasticity in the CA3 region of the hippocampal slice. Long-term potentiation (LTP) of the mossy fiber-CA3 synapse was blocked by muscarine. Low concentrations of muscarine (1 micromolar) had little effect on low-frequency (0.2 hertz) synaptic stimulation but did significantly reduce the magnitude and probability of induction of LTP. Experiments under voltage clamp showed that muscarine blocked the increase in excitatory synaptic conductance normally associated with LTP at this synapse. These results suggest a possible role for cholinergic systems in synaptic plasticity.
Single Subunits of the GABA
A
Receptor Form Ion Channels with Properties of the Native Receptor
Authors: Blair Leslie A. C. , Levitan Edwin S. , Marshall John , Dionne Vincent E. , Barnard Eric A.
Published: October 2006

The α and β subunits of the γ-aminobutyric acidA (GABA
A
) receptor were expressed individually in
Xenopus
oocytes by injection of RNA synthesized from their cloned DNAs. GABA-sensitive chloride channels were detected several days after injection with any one of three different α RNAs (α
1
, α
2
, and α
3
) or with β RNA. The channels induced by each of the α-subunit RNAs were indistinguishable, they had multiple conductance levels (10, 19, 28, and 42 picosiemens), and their activity was potentiated by pentobarbital and inhibited by picrotoxin. The β channels usually expressed poorly but showed similar single channel conductance levels (10, 18, 27, and 40 picosiemens), potentiation by pentobarbital and inhibition by picrotoxin. The finding that both α and β subunits, examined separately, form GABA-sensitive ion channels with permeation properties and regulatory sites characteristic of the native receptor suggests that the amino acid sequences that confer these properties are within the homologous domains shared by the subunits.
Reduced Numbers of Somatostatin Receptors in the Cerebral Cortex in Alzheimer's Disease
Authors: Beal M. Flint , Mazurek Michael F. , Tran Vinh T. , Chattha Geetinder , Bird Edward D. , Martin Joseph B.
Published: October 2006

Somatostatin receptor concentrations were measured in patients with Alzheimer's disease and controls. In the frontal cortex (Brodmann areas 6, 9, and 10) and temporal cortex (Brodmann area 21), the concentrations of somatostatin in receptors in the patients were reduced to approximately 50 percent of control values. A 40 percent reduction was seen in the hippocampus, while no significant changes were found in the cingulate cortex, postcentral gyrus, temporal pole, and superior temporal gyrus. Scatchard analysis showed a reduction in receptor number rather than a change in affinity. Somatostatin-like immunoreactivity was significantly reduced in both the frontal and temporal cortex. Somatostatin-like immunoreactivity was linearly related to somatostatin-receptor binding in the cortices of Alzheimer's patients. These findings may reflect degeneration of postsynaptic neurons or cortical afferents in the patients' cerebral cortices. Alternatively, decreased somatostatin-like immunoreactivity in Alzheimer's disease might indicate increased release of somatostatin and down regulation of postsynaptic receptors.
Region-Specific Expression of Two Mouse Homeo Box Genes
Authors: Utset Manuel F. , Awgulewitsch Alexander , Ruddle Frank H. , McGinnis William
Published: October 2006

Mammalian homeo box genes have been identified on the basis of sequence homology to
Drosophila
homeotic and segmentation genes. These studies examine the distribution of transcripts from two mouse homeo box genes, Hox-2.1 and Hox-3.1, throughout the latter third of prenatal development. Transcripts from these genes are regionally localized along the rostro-caudal axis of the developing central nervous system, yielding expression patterns very similar to patterns of
Drosophila
homeotic gene expression.
F-actin and Microtubule Suspensions as Indeterminate Fluids
Authors: Buxbaum Robert E. , Dennerll Timothy , Weiss Serge , Heidemann Steven R.
Published: October 2006

The viscosity of F-actin and microtubule suspensions has been measured as a function of shear rate with a Weissenberg rheogoniometer. At shear rates of less than 1.0 per second the viscosity of suspensions of these two structural proteins is inversely proportional to shear rate. These results are consistent with previous in vivo measurements of the viscosity of cytoplasm. This power law implies that shear stress is independent of shear rate; that is, shear stress is a constant at all shear rates less than 1.0 per second. Thus the flow profile of these fluids is indeterminate, or nearly so. This flow property may explain several aspects of intracellular motility in living cells. Possible explanations for this flow property are based on a recent model for semidilute suspensions of rigid rods or a classical friction model for liquid crystals.
Expression and Function of the Segmentation Gene
fushi tarazu
During
Drosophila
Neurogenesis
Authors: Doe Chris Q. , Hiromi Yasushi , Gehring Walter J. , Goodman Corey S.
Published: October 2006

Segmentation genes control cell identities during early pattern formation in
Drosophila
. One of these genes,
fushi tarazu
(
ftz
), is now shown also to control cell fate during neurogenesis. Early in development,
ftz
is expressed in a striped pattern at the blastoderm stage. Later, it is transiently expressed in a specific subset of neuronal precursor cells, neurons (such as aCC, pCC, RP1, and RP2), and glia in the developing central nervous system (CNS). The function of
ftz
in the CNS was determined by creating
ftz
mutant embryos that express
ftz
in the blastoderm stripes but not in the CNS. In the absence of
ftz
CNS expression, some neurons appear normal (for example, the aCC, pCC, and RP1), whereas the RP2 neuron extends its growth cone along an abnormal pathway, mimicking its sibling (RP1), suggesting a transformation in neuronal identity.
Quinoxalinediones: Potent Competitive Non-NMDA Glutamate Receptor Antagonists
Authors: Honoré Tage , Davies Steve N. , Drejer Jørgen , Fletcher Elizabeth J. , Jacobsen Poul , Lodge David , Nielsen Flemming E.
Published: October 2006

The
N
-methyl-D-aspartate (NMDA)-subtype of glutamate receptors has been well described as a result of the early appearance of NMDA antagonists, but no potent antagonist for the "non-NMDA" glutamate receptors has been available. Quinoxalinediones have now been found to be potent and competitive antagonists at non-NMDA glutamate receptors. These compounds will be useful in the determination of the structure-activity relations of quisqualate and kainate receptors and the role of such receptors in synaptic transmission in the mammalian brain.
Repair of the Secretion Defect in the Z Form of α1-Antitrypsin by Addition of a Second Mutation
Authors: Brantly Mark , Courtney Michael , Crystal Ronald G.
Published: October 2006

Homozygous inheritance of the Z-type mutant form of the α1-antitrypsin (α1AT) gene results in the most common form of α1AT deficiency, a human hereditary disease associated with a high risk for the development of emphysema and an increased incidence of neonatal hepatitis. The α1AT-synthesizing cells of individuals with the Z gene have normal α1AT messenger RNA levels, but α1AT secretion is markedly reduced secondary to accumulation of newly synthesized α1AT in the rough endoplasmic reticulum. Crystallographic analysis of α1AT predicts that in normal α1AT, a negatively charged Glu
342
is adjacent to positively charged Lys
290
. Thus the Glu
342
→ Lys
342
Z mutation causes the loss of a normal salt bridge, resulting in the intracellular aggregation of the Z molecule. The prediction was made that a second mutation in the α1AT gene that changed the positively charged Lys
290
to a negatively charged Glu
290
would correct the secretion defect. When the second mutation was added to the Z-type complementary DNA, the resulting gene directed the synthesis and secretion of amounts of α1AT similar to that directed by the normal α1AT complementary DNA in an in vitro eukaryotic expression system. This suggests the possibility that a human hereditary disease can be corrected by inserting an additional mutation in the same gene.
Phylogenetic Meaning of the Kingdom Concept: an Unusual Ribosomal RNA from
Giardia lamblia
Authors: Sogin Mitchell L. , Gunderson John H. , Elwood Hille J. , Alonso Rogelio A. , Peattie Debra A.
Published: October 2006

An analysis of the small subunit ribosomal RNA (16
S
-like rRNA) from the protozoan
Giardia lamblia
provided a new perspective on the evolution of nucleated cells. Evolutionary distances estimated from sequence comparisons between the 16
S
-like rRNAs of
Giardia lamblia
and other eukaryotes exceed similar estimates of evolutionary diversity between archaebacteria and eubacteria and challenge the phylogenetic significance of multiple eukaryotic kingdoms. The
Giardia lamblia
16
S
-like rRNA has retained many of the features that may have been present in the common ancestor of eukaryotes and prokaryotes.
A New Cluster of Genes Within the Human Major Histocompatibility Complex
Authors: Spies Thomas , Blanck George , Bresnahan Maureen , Sands John , Strominger Jack L.
Published: October 2006

A 435-kilobase (kb) DNA segment, which is centromeric to HLA-B in the human major histocompatibility complex, was isolated by chromosome walking with overlapping cosmids. Within the cloned region, the genes for the tumor necrosis factors (TNFs) α and β and HLA-B were 210 kb apart. The human homolog of a mouse gene, B
144
, was located next to TNFα. Moreover, the presence of additional genes was suggested by a large cluster of CpG islands. With cosmid probes, several distinct transcripts were detected in RNA samples from a variety of cell lines. Altogether, five novel genes were identified by isolation of corresponding complementary DNA clones. These "HLA-B-associated transcripts" (BATs) were mapped to different locations within a 160-kb region that includes the genes for TNFα and TNFβ. The presence of the genes for BAT1 to BAT5 in the vicinity of HLA-B again raises the question of which gene in this region determines susceptibility to ankylosing spondylitis.
Atrial Natriuretic Factor Ameliorates Chronic Metabolic Alkalosis by Increasing Glomerular Filtration
Authors: Cogan Martin G.
Published: October 2006

The kidney maintains the elevated plasma concentration of bicarbonate that occurs in chronic metabolic alkalosis. A reduction in the glomerular filtration rate (GFR) can maintain the filtered bicarbonate load at a normal level so that a normal rate of bicarbonate reabsorption suffices to prevent urinary excretion of this anion. It is also possible that bicarbonate reabsorption might increase so as to maintain the alkalosis if GFR were not reduced. To examine this latter possibility, atrial natriuretic factor was used in alkalotic rats to restore a more normal GFR and to increase the amount of bicarbonate filtered by the glomerulus. Proximal bicarbonate reabsorption remained relatively static. Higher than normal amounts of bicarbonate were then delivered out of the proximal tubule, bicarbonate appeared in the urine, and the plasma concentration of bicarbonate fell. A reduction in GFR is thus necessary for the maintenance of chronic metabolic alkalosis. Normalizing GFR induces bicarbonaturia and initiates repair of the alkalosis.