bluuebunny/crossref_metadata_2025 huggingface dataset:
Closing In on Cosmic Expansion
Authors: Finkbeiner Ann
Published: October 2006

The battle over the Hubble constant, the rate at which the universe is expanding, has raged for decades, fueled by the difficulty of measuring cosmic distances. One camp favored an expansion rate that implies an aged universe, the other a rate that implies a universe seemingly younger than the oldest stars. Supernovas may finally be breaking the impasse by giving astronomers a trustworthy “standard candle”—an object whose faintness is a true indicator of distance. They put the cosmos in comfortable middle age.
Naked Quasars Get Dressed
Authors: Kaiser Jocelyn
Published: October 2006

Early this year, astronomers trying to understand quasars—objects that shine with the brilliance of millions of stars from the far edges of the universe—got a shock. Theorists assumed that each of these beacons is powered by a giant black hole sucking in material from a surrounding galaxy. But when the Hubble Space Telescope provided the first clear look at quasars, the host galaxies seemed to be missing. Now a reanalysis of the same images suggests that the galaxies were there all along.
Self-Organization of CdSe Nanocrystallites into Three-Dimensional Quantum Dot Superlattices
Authors: Murray C. B. , Kagan C. R. , Bawendi M. G.
Published: October 2006

The self-organization of CdSe nanocrystallites into three-dimensional semiconductor quantum dot superlattices (colloidal crystals) is demonstrated. The size and spacing of the dots within the superlattice are controlled with near atomic precision. This control is a result of synthetic advances that provide CdSe nanocrystallites that are monodisperse within the limit of atomic roughness. The methodology is not limited to semiconductor quantum dots but provides general procedures for the preparation and characterization of ordered structures of nanocrystallites from a variety of materials.
North Atlantic Deepwater Temperature Change During Late Pliocene and Late Quaternary Climatic Cycles
Authors: Dwyer Gary S. , Cronin Thomas M. , Baker Paul A. , Raymo Maureen E. , Buzas Jeffrey S. , Corrège Thierry
Published: October 2006

Variations in the ratio of magnesium to calcium (Mg/Ca) in fossil ostracodes from Deep Sea Drilling Project Site 607 in the deep North Atlantic show that the change in bottom water temperature during late Pliocene 41,000-year obliquity cycles averaged 1.5°C between 3.2 and 2.8 million years ago (Ma) and increased to 2.3°C between 2.8 and 2.3 Ma, coincidentally with the intensification of Northern Hemisphere glaciation. During the last two 100,000-year glacial-to-interglacial climatic cycles of the Quaternary, bottom water temperatures changed by 4.5°C. These results show that glacial deepwater cooling has intensified since 3.2 Ma, most likely as the result of progressively diminished deepwater production in the North Atlantic and of the greater influence of Antarctic bottom water in the North Atlantic during glacial periods. The ostracode Mg/Ca data also allow the direct determination of the temperature component of the benthic foraminiferal oxygen isotope record from Site 607, as well as derivation of a hypothetical sea-level curve for the late Pliocene and late Quaternary. The effects of dissolution on the Mg/Ca ratios of ostracode shells appear to have been minimal.
Sequence and Characterization of a Coactivator for the Steroid Hormone Receptor Superfamily
Authors: Oñate Sergio A. , Tsai Sophia Y. , Tsai Ming-Jer , O'Malley Bert W.
Published: October 2006

A yeast two-hybrid system was used to identify a protein that interacts with and enhances the human progesterone receptor (hPR) transcriptional activity without altering the basal activity of the promoter. Because the protein stimulated transactivation of all the steroid receptors tested, it has been termed steroid receptor coactivator-1 (SRC-1). Coexpression of SRC-1 reversed the ability of the estrogen receptor to squelch activation by hPR. Also, the amino terminal truncated form of SRC-1 acted as a dominant-negative repressor. Together, these results indicate that SRC-1 encodes a coactivator that is required for full transcriptional activity of the steroid receptor superfamily.
Self-Release of CLIP in Peptide Loading of HLA-DR Molecules
Authors: Kropshofer Harald , Vogt Anne B. , Stern Lawrence J. , Hämmerling Günter J.
Published: October 2006

The assembly and transport of major histocompatibility complex (MHC) class II molecules require interaction with the invariant chain. A fragment of the invariant chain, CLIP, occupies the peptide-binding groove of the class II molecule. At endosomal pH, the binding of CLIP to human MHC class II HLA-DR molecules was counteracted by its amino-terminal segment (residues 81 to 89), which facilitated rapid release. The CLIP(81–89) fragment also catalyzed the release of CLIP(90–105) and a subset of other self-peptides, probably by transient interaction with an effector site outside the groove. Thus, CLIP may facilitate peptide loading through an allosteric release mechanism.
Scope of the AIDS Epidemic in the United States
Authors: Rosenberg Philip S.
Published: October 2006

Two-dimensional deconvolution techniques are used here to reconstruct age-specific human immunodeficiency virus (HIV) infection rates in the United States from surveillance data on acquired immunodeficiency syndrome (AIDS). This approach suggests that 630,000 to 897,000 adults and adolescents in the United States were living with HIV infection as of January 1993, including 107,000 to 150,000 women. The estimated incidence of HIV infection declined markedly over time among white males, especially those older than 30 years. In contrast, HIV incidence appears to have remained relatively constant among women and minorities. As of January 1993, prevalence was highest among young adults in their late twenties and thirties and among minorities. An estimated 3 percent of black men and 1 percent of black women in their thirties were living with HIV infection as of that date. If infection rates remain at these levels, HIV must be considered as endemic in the United States.
Are Wildlife Corridors the Right Path?
Authors: Mann Charles C. , Plummer Mark L.
Published: October 2006

The popular strategy of connecting patches of otherwise isolated habitat is at the center of a major conservation debate. Many ecologists and conservation activists argue that such corridors are critical to maintaining biodiversity and could save many endangered species. But others counter that there is little evidence that animals need these corridors and that buying corridor land precludes spending money on more scientifically certain conservation efforts.
Why Mammal Ears Went on the Move
Authors: Fischman Joshua
Published: October 2006

The mark of a mammal is a migrating ear. A chain of small bones that used to be part of the jaw moved back to the skull and became the middle ear—a journey that set true mammals apart from every other vertebrate. A new theory argues that this mysterious transformation of jaw and ear was actually driven by a different body part: the expansion of the brain.
Model Enzyme Takes Hydrogen Apart
Authors: Service Robert F.
Published: October 2006

Splitting hydrogen into its components is a life-or-death reaction for anaerobic bacteria, and biochemists have long struggled to learn how a crucial enzyme—hydrogenase—carries this out. Now a new model enzyme, a simplified version of hydrogenase, is revealing the steps of hydrogen disassembly.
Needed: Coherent Budgeting for Science and Technology
Authors: Press Frank
Published: October 2006

A new report from the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine suggests changes in the processes for allocating federal funds for science and technology. The author of this Policy Forum, the chair of the report committee, describes the key recommendations of the report for a new way of budgeting federal investments in science and technology, why the committee urges the change, and the implications for both the federal budget process in the Administration and Congress and the future strength of American science and technology.
The United Nations Climate Convention: Unattainable or Irrelevant
Authors: Kauppi Pekka E.
Published: October 2006

P. Kauppi argues that the recommendation of the UN Climate Convention (“… to stabilize … greenhouse gas concentrations [to] … prevent dangerous anthropogenic interference with the climate system”) is laudable, but likely cannot be achieved.
Phase Diagram of Iron by in Situ X-ray Diffraction: Implications for Earth's Core
Authors: Yoo C. S. , Akella J. , Campbell A. J. , Mao H. K. , Hemley R. J.
Published: October 2006

The phase diagram of iron has been studied to 130 gigapascals (1 gigapascal = 10
4
atmospheres) and 3500 kelvin by a combined laser-heated diamond-anvil cell and x-ray diffraction technique that provides direct identification of the solid phases. Iron in the hexagonal close-packed (hcp) phase (ε-Fe) is stable from 50 to at least 110 gigapascals at high temperatures. The wide stability field of ε-Fe indicates that this polymorph should currently be considered the most relevant solid phase for Earth's core. The triple point between the γ, ε, and liquid phases is located at 2500 ± 200 kelvin and 50 ± 10 gigapascals. There is evidence for a phase with a double hcp structure below 40 gigapascals and for another transition above 110 gigapascals and 3000 kelvin.
Infrared Spectrum of the Cool Brown Dwarf Gl 229B
Authors: Oppenheimer B. R. , Kulkarni S. R. , Matthews K. , Nakajima T.
Published: October 2006

Spectroscopic measurements of a cool brown dwarf, Gl 229B, reveal absorption features attributable to methane in the near infrared much like those of Jupiter. These features are not seen in any star. The presence of methane indicates that the surface temperature of Gl 229B is below 1000 kelvin. Features attributed to water vapor also indicate that Gl 229B is much cooler than any known star.
Molecular Organization of Surfactants at Solid-Liquid Interfaces
Authors: Manne Srinivas , Gaub Hermann E.
Published: October 2006

Interactions between surfactant solutions and solid surfaces play a key role in technologically important processes such as colloidal stabilization, ore flotation, and soil removal; however, the interfacial aggregation of surfactant molecules is not yet well understood. Direct images of surfactant aggregates at solid surfaces in aqueous solutions were obtained with atomic force microscopy. The resulting structures for quaternary ammonium surfactants (above the critical micelle concentration) are consistent with half-cylinders on crystalline hydrophobic substrates, full cylinders on mica, and spheres on amorphous silica. These structures-surprisingly different from earlier models-appear to result from a compromise between the natural free curvature as defined by intermolecular interactions and the constraints imposed by specific surfactant-surface interactions. Such interfacial aggregates can potentially be used to pattern surfaces at nanometer-length scales.
Autoencapsulation Through Intermolecular Forces: A Synthetic Self-Assembling Spherical Complex
Authors: Meissner Robert S. , Rebek Julius , de Mendoza Javier
Published: October 2006

The synthesis and characterization of a system for the study of molecular recognition phenomena are described. The system involves a tetraurea molecule that is capable of assembly into various associated states through hydrogen bonding. In organic solvents, the dynamic transition between a low-ordered (aggregate) state and a highly ordered dimeric assembly can be induced by the introduction of smaller molecules of appropriate size and shape. These smaller molecules, such as benzene, adamantanes, and ferrocenes, act as guests that occupy the pseudospherical capsule formed by the dimeric host. Among various guests, those that best fill the cavity and offer chemical complementarity to the host are preferentially encapsulated.
Yeast Checkpoint Genes in DNA Damage Processing: Implications for Repair and Arrest
Authors: Lydall David , Weinert Ted
Published: October 2006

Yeast checkpoint control genes were found to affect processing of DNA damage as well as cell cycle arrest. An assay that measures DNA damage processing in vivo showed that the checkpoint genes
RAD17, RAD24
, and
MEC3
activated an exonuclease that degrades DNA. The degradation is probably a direct consequence of checkpoint protein function, because
RAD17
encodes a putative 3′-5′ DNA exonuclease. Another checkpoint gene,
RAD9
, had a different role: It inhibited the degradation by
RAD17
,
RAD24
, and
MEC3
. A model of how processing of DNA damage may be linked to both DNA repair and cell cycle arrest is proposed.
Missing Chunk of North America Found in Argentina
Authors: Kerr Richard A.
Published: October 2006

Geologists have been mystified by the wanderings of North America during a crucial period 500 million years ago, when many of the life forms known today were evolving. Now a chunk of crust in western Argentina is turning out to be North America's calling card. Dropped off in western South America nearly 500 million years ago, it pins down the errant North America to within a few thousand kilometers of South America's west coast.
Plasma Physicists Seek New Uses for the Legacy of Fusion
Authors: Glanz James
Published: October 2006

Louisville—The magnetic fusion program may be in tatters after Congressional budget cuts, but plasma physicists are applying fusion hardware and concepts to new problems. At a meeting here, one group reported using a fusion machine to study how pressure fluctuations in a plasma can drive a natural dynamo, producing a magnetic field—a process that may be responsible for some of the magnetic fields that thread the cosmos. Two other groups described schemes for turning fusion devices into rocket thrusters. A fourth line of work may have solved a problem that plagued fusion studies: explosions within plasmas that theory says should be stable.
Histones Hush Yeast Mating Genes
Authors: Nowak Rachel
Published: October 2006

The discovery of how DNA is wrapped around histone cores suggests the possibility that histones might have a role to play in regulating the activity of specific genes. That idea fell into disrepute, however, as a great deal of evidence pointed at the importance of the proteins called transcription factors for specific gene regulation. But within the past year or two, researchers have found that histones can have a targeted effect on genes, suppressing the activity of some, but not others, in a phenomenon called gene silencing.
Chromosomal Control of Meiotic Cell Division
Authors: McKim Kim S. , Hawley R. Scott
Published: October 2006

Chromosomes have multiple roles both in controlling the cell assembly and structure of the spindle and in determining chromosomal position on the spindle in many meiotic cells and in some types of mitotic cells. Moreover, functionally significant chromosome-microtubule interactions are not limited to the kinetochore but are also mediated by proteins localized along the arms of chromosomes. Finally, chromosomes also play a crucial role in control of the cell cycle.
Telomeres: Beginning to Understand the End
Authors: Zakian Virginia A.
Published: October 2006

Telomeres are the protein-DNA structures at the ends of eukaryotic chromosomes. In yeast, and probably most other eukaryotes, telomeres are essential. They allow the cell to distinguish intact from broken chromosomes, protect chromosomes from degradation, and are substrates for novel replication mechanisms. Telomeres are usually replicated by telomerase, a telomere-specific reverse transcriptase, although telomerase-independent mechanisms of telomere maintenance exist. Telomere replication is both cell cycle- and developmentally regulated, and its control is likely to be complex. Because telomere loss causes the kinds of chromosomal changes associated with cancer and aging, an understanding of telomere biology has medical relevance.
Equality for X Chromosomes
Authors: Kelley Richard L. , Kuroda Mitzi I.
Published: October 2006

In many species, females possess two X chromosomes and males have one X chromosome. This difference is critical for the initial determination of sex. However, the X encodes many functions required equally in males and females; thus, X chromosome expression must be adjusted to compensate for the difference in dosage between the sexes. Distinct dosage compensation mechanisms have evolved in different species. A common theme in the
Drosophila melanogaster
and
Caenorhabditis elegans
systems is that a subtle alteration of chromatin structure may impose this modest, but vital adjustment of the X chromosome transcription level.
Behavior of the Heliosphere over Prolonged Solar Quiet Periods by
44
Ti Measurements in Meteorites
Authors: Bonino G. , Castagnoli G. Cini , Bhandari N. , Taricco C.
Published: October 2006

The heliospheric magnetic field (HMF) is controlled by solar activity, as established by measurements over the last few decades, but its characteristics when the sun was quiet for prolonged periods, such as during Gleissberg or Maunder minima, are not known. Titanium-44, produced in meteorites, provides a monitor of the galactic cosmic ray (GCR) flux and allows estimation of the modulation effect of the sun for the period 1883 to 1992. The titanium-44 activity is consistent with the expected value, but the increase, due to the last Gleissberg minimum, is four times greater than expected for a GCR modulation based solely on sunspot numbers. This result implies that the HMF was weaker than at present and as a result the GCR flux (for energy greater than 1 gigaelectron volt) was higher between 2.2 to 3.6 protons per square centimeter per second per 4π steradians at 1 to 3 astronomical units in solar cycles 12 to 15.
Particle Formation in the Upper Tropical Troposphere: A Source of Nuclei for the Stratospheric Aerosol
Authors: Brock C. A. , Hamill P. , Wilson J. C. , Jonsson H. H. , Chan K. R.
Published: October 2006

Atmospheric measurements and numerical calculations described here indicate that binary homogeneous nucleation of H
2
SO
4
-H
2
O particles occurs in the upper tropical troposphere. Particle concentrations decrease with increasing altitude above the tropical tropopause as a result of coagulation during the upward air transport produced by stratospheric circulations. During the extended periods of time that volcanic eruptions do not strongly influence stratospheric particle number concentrations, particles formed in the upper tropical troposphere provide nuclei upon which oxidized sulfur gases condense in the stratosphere. This particle source, coupled with aerosol microphysical properties and atmospheric transport, governs the number concentration of particles in the lower tropical and mid-latitude stratosphere.
Transcription Against an Applied Force
Authors: Yin Hong , Wang Michelle D. , Svoboda Karel , Landick Robert , Block Steven M. , Gelles Jeff
Published: October 2006

The force produced by a single molecule of
Escherichia coli
RNA polymerase during transcription was measured optically. Polymerase immobilized on a surface was used to transcribe a DNA template attached to a polystyrene bead 0.5 micrometer in diameter. The bead position was measured by interferometry while a force opposing translocation of the polymerase along the DNA was applied with an optical trap. At saturating nucleoside triphosphate concentrations, polymerase molecules stalled reversibly at a mean applied force estimated to be 14 piconewtons. This force is substantially larger than those measured for the cytoskeletal motors kinesin and myosin and exceeds mechanical loads that are estimated to oppose transcriptional elongation in vivo. The data are consistent with efficient conversion of the free energy liberated by RNA synthesis into mechanical work.
Conserved Initiator Proteins in Eukaryotes
Authors: Gavin Kimberley A. , Hidaka Masumi , Stillman Bruce
Published: October 2006

The origin recognition complex (ORC), a multisubunit protein identified in
Saccharomyces cerevisiae
, binds to chromosomal replicators and is required for the initiation of cellular DNA replication. Complementary DNAs (cDNAs) encoding proteins related to the two largest subunits of ORC were cloned from various eukaryotes. The cDNAs encoding proteins related to
S. cerevisiae
Orc1p were cloned from the budding yeast
Kluyveromyces lactis
, the fission yeast
Schizosaccharomyces pombe,
and human cells. These proteins show similarity to regulators of the S and M phases of the cell cycle. Genetic analysis of
orc1
+
from
S. pombe
reveals that it is essential for cell viability. The cDNAs encoding proteins related to
S. cerevisiae
Orc2p were cloned from
Arabidopsis thaliana, Caenorhabditis elegans
, and human cells. The human ORC-related proteins interact in vivo to form a complex. These studies suggest that ORC subunits are conserved and that the role of ORC is a general feature of eukaryotic DNA replication.
Separation of Origin Recognition Complex Functions by Cross-Species Complementation
Authors: Ehrenhofer-Murray Ann E. , Gossen Manfred , Pak Daniel T. S. , Botchan Michael R. , Rine Jasper
Published: October 2006

Transcriptional silencing at the
HMR
a locus of
Saccharomyces cerevisiae
requires the function of the origin recognition complex (ORC), the replication initiator of yeast. Expression of a
Drosophila melanogaster Orc2
complementary DNA in the yeast
orc2-1
strain, which is defective for replication and silencing, complemented the silencing defect but not the replication defect; this result indicated that the replication and silencing functions of ORC were separable. The
orc2-1
mutation mapped to the region of greatest homology between the
Drosophila
and yeast proteins. The silent state mediated by
DmOrc2
was epigenetic; it was propagated during mitotic divisions in a relatively stable way, whereas the nonsilent state was metastable. In contrast, the silent state was erased during meiosis.
R&D Impact: A Numbers Game?
Authors: Mervis Jeffrey
Published: October 2006

Democratic leaders have been using a sheaf of statistics to support their arguments for increasing federal funds for industrial research. The Republicans have been arguing that these funds should be cut; given the right economic environment, they say, corporations don't need government support. Experts who have been following these arguments say the rhetoric and statistics from both sides should be taken with a grain of salt.
Tech Funding: If U.S. Bows Out, States May Come Up Short
Authors: Roush Wade
Published: October 2006

Boston—The federal side of cooperative state technology programs looks as if it's melting away. Republicans have proposed canceling the U.S. Department of Commerce's Advanced Technology Program (ATP), calling it “corporate welfare” and arguing that states and private industry will pick up the slack. Some state technology officials have a darker view, saying that hundreds of companies and researchers may be left in the cold.
Less Hype, More Biology Needed for Gene Therapy
Authors: Marshall Eliot
Published: October 2006

A tough review of the state of the art in gene therapy has concluded that the technology has been oversold, there are few unambiguous examples in which patients have benefited from the technique, and the National Institutes of Health has supported too many clinical trials that are of limited scientific value. The bottom line: More research is needed to improve basic gene transfer techniques. (Report is available from the World Wide Web at
http://www.nih.gov/news/panelrep.html
).
Fusion Advocates Scramble for Scraps
Authors: Lawler Andrew
Published: October 2006

The bottom is dropping out of the budget for the U.S. fusion program, and the Department of Energy is trying to put together plans for a far more modest effort. Members of a key advisory committee want the department to do more than simply accept the cuts, however.
Plutonium Under Glass
Authors: Service Robert F.
Published: October 2006

Wherever the United States decides to put its high-level nuclear waste, planners must also decide how to store a particularly worrisome component: plutonium. At the Materials Research Society meeting in Boston 2 weeks ago, researchers presented a new scheme for putting plutonium safely under glass. The formulation, involving alkali metals, has the potential to incorporate up to 10% plutonium by weight, much more than other types of waste glass.
Ethylene Sensors: How Perceptive!
Authors: Theologis Athanasios
Published: October 2006

A. Theologis provides an update of the search for ethylene receptors in plants. Two papers in this issue of
Science
(Shaller and Bleecker,
p. 1809
, and Wilkinson
et al.
,
p. 1807
) provide evidence that the putative ethylene receptor ETR1 can actually bind ethylene and that ethylene sensors are encoded by multigene families with members that are differentially expressed during plant growth and development.
Multiple TAF
II
s Directing Synergistic Activation of Transcription
Authors: Sauer Frank , Hansen Stig K. , Tjian Robert
Published: October 2006

Coordinate activation of transcription by multiple enhancer binding factors is essential for the regulation of pattern formation during development of
Drosophila melanogaster
. Cell-free transcription reactions are described that recapitulate transcriptional synergism directed by the
Drosophila
developmental regulators Bicoid (BCD) and Hunchback (HB). Within the basal transcription factor complex TFIID, two specific targets, TAF
II
110 and TAF
II
60, served as coactivators to mediate transcriptional activation by these two enhancer binding proteins. A quadruple complex containing TATA binding protein (TBP), TAF
II
250, TAF
II
110, and TAF
II
60 mediated transcriptional synergism by BCD and HB, whereas triple TBP-TAF
II
complexes lacking one or the other target coactivator failed to support synergistic activation. Deoxyribonuclease I footprint protection experiments revealed that an integral step leading to transcriptional synergism involves the recruitment of TBP-TAF
II
complexes to the promoter by way of multivalent contacts between activators and selected TAF
II
s. Thus, the concerted action of multiple regulators with different coactivators helps to establish the pattern and level of segmentation gene transcription during
Drosophila
development.
Polymer Photovoltaic Cells: Enhanced Efficiencies via a Network of Internal Donor-Acceptor Heterojunctions
Authors: Yu G. , Gao J. , Hummelen J. C. , Wudl F. , Heeger A. J.
Published: October 2006

The carrier collection efficiency (η
c
) and energy conversion efficiency (η
e
) of polymer photovoltaic cells were improved by blending of the semiconducting polymer with C
60
or its functionalized derivatives. Composite films of poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) and fullerenes exhibit η
c
of about 29 percent of electrons per photon and η
e
of about 2.9 percent, efficiencies that are better by more than two orders of magnitude than those that have been achieved with devices made with pure MEH-PPV. The efficient charge separation results from photoinduced electron transfer from the MEH-PPV (as donor) to C
60
(as acceptor); the high collection efficiency results from a bicontinuous network of internal donor-acceptor heterojunctions.
Shock-Excited OH Maser Emission Outlining the Galactic Center Supernova Remnant G359.1-0.05
Authors: Yusef-Zadeh F. , Uchida K. I. , Roberts D.
Published: October 2006

A search using the Very Large Array was performed for 1720-megahertz OH maser line emission from a number of nonthermal radio continuum sources in the galactic center region. The 1720-megahertz transition has recently been noted for its potential as a tracer of shock activity. The most striking result was the detection of extended 1720-megahertz OH maser emission, as well as a number of compact OH maser features, along the interface between a large-scale continuum shell (G359.1-0.5) and its surrounding ring of high-velocity molecular gas. The morphological correlation among the neutral gas, the nonthermal shell, and the maser features provides strong support for the hypothesis that the 1720-megahertz maser line of OH arises from gas shocked by the impact of the expanding supernova remnant into the molecular material. However, the radial velocities of the molecular cloud surrounding G359.1-0.5 are more negative than that of the OH maser spots by more than 50 kilometers per second. Here it is suggested that only the low-radial-velocity component of the carbon monoxide material at the limb of the remnant satisfies the physical conditions required for collisional pumping of the OH 1720-megahertz line behind the expanding shock front.
A Receptor Kinase-Like Protein Encoded by the Rice Disease Resistance Gene,
Xa21
Authors: Song Wen-Yuan , Wang Guo-Liang , Chen Li-Li , Kim Han-Suk , Pi Li-Ya , Holsten Tom , Gardner J. , Wang Bei , Zhai Wen-Xue , Zhu Li-Huang , Fauquet Claude , Ronald Pamela
Published: October 2006

The rice
Xa21
gene, which confers resistance to
Xanthomonas oryzae
pv.
oryzae
race 6, was isolated by positional cloning. Fifty transgenic rice plants carrying the cloned
Xa21
gene display high levels of resistance to the pathogen. The sequence of the predicted protein, which carries both a leucine-rich repeat motif and a serine-threonine kinase-like domain, suggests a role in cell surface recognition of a pathogen ligand and subsequent activation of an intracellular defense response. Characterization of
Xa21
should facilitate understanding of plant disease resistance and lead to engineered resistance in rice.
An Ethylene-Inducible Component of Signal Transduction Encoded by
Never-ripe
Authors: Wilkinson Jack Q. , Lanahan Michael B. , Yen Hsiao-Ching , Giovannoni James J. , Klee Harry J.
Published: October 2006

The ripening-impaired tomato mutant
Never-ripe
(
Nr
) is insensitive to the plant hormone ethylene. The gene that cosegregates with the
Nr
locus encodes a protein with homology to the
Arabidopsis
ethylene receptor ETR1 but is lacking the response regulator domain found in ETR1 and related prokaryotic two-component signal transducers. A single amino acid change in the sensor domain confers ethylene insensitivity when expressed in transgenic tomato plants. Modulation of
NR
gene expression during fruit ripening controls response to the hormone ethylene.
Crystal Structure of the V
α
Domain of a T Cell Antigen Receptor
Authors: Fields Barry A. , Ober Bertram , Malchiodi Emilio L. , Lebedeva Marina I. , Braden Bradford C. , Ysern Xavier , Kim Jin-Kyoo , Shao Xuguang , Ward E. Sally , Mariuzza Roy A.
Published: October 2006

The crystal structure of the V
α
domain of a T cell antigen receptor (TCR) was determined at a resolution of 2.2 angstroms. This structure represents an immunoglobulin topology set different from those previously described. A switch in a polypeptide strand from one β sheet to the other enables a pair of V
α
homodimers to pack together to form a tetramer, such that the homodimers are parallel to each other and all hypervariable loops face in one direction. On the basis of the observed mode of V
α
association, a model of an (αβ)
2
TCR tetramer can be positioned relative to the major histocompatibility complex class II (αβ)
2
tetramer with the third hypervariable loop of V
α
over the amino-terminal portion of the antigenic peptide and the corresponding loop of V
β
over its carboxyl-terminal residues. TCR dimerization that is mediated by the α chain may contribute to the coupling of antigen recognition to signal transduction during T cell activation.
Precise Spatial Positioning of Chromosomes During Prometaphase: Evidence for Chromosomal Order
Authors: Nagele Robert , Freeman Theresa , McMorrow Lydia , Lee Hsin-yi
Published: October 2006

The relative locations of several chromosomes within wheel-shaped prometaphase chromosome rosettes of human fibroblasts and HeLa cells were determined with fluorescence hybridization. Homologs were consistently positioned on opposite sides of the rosette, which suggests that chromosomes are separated into two haploid sets, each derived from one parent. The relative locations of chromosomes on the rosette were mapped by dual hybridizations. The data suggest that the chromosome orders within the two haploid sets are antiparallel. This chromosome arrangement in human cells appears to be both independent of cell type- and species-specific and may influence chromosome topology throughout the cell cycle.
Role of NK1.1
+
T Cells in a T
H
2 Response and in Immunoglobulin E Production
Authors: Yoshimoto Tomohiro , Bendelac Albert , Watson Cynthia , Hu-Li Jane , Paul William E.
Published: October 2006

Immune responses dominated by interleukin-4 (IL-4)-producing T helper type 2 (T
H
2) cells or by interferon γ (IFN-γ)-producing T helper type 1 (T
H
1) cells express distinctive protection against infection with different pathogens. Interleukin-4 promotes the differentiation of naïve CD4
+
T cells into IL-4 producers and suppresses their development into IFN-γ producers. CD1-specific splenic CD4
+
NK1.1
+
T cells, a numerically minor population, produced IL-4 promptly on in vivo stimulation. This T cell population was essential for the induction of IL-4-producing cells and for switching to immunoglobulin E, an IL-4-dependent event, in response to injection of antibodies to immunoglobulin D.
Suit Alleges Misuse of Peer Review
Authors: Marshall Eliot
Published: October 2006

A lawsuit, headed for trial in Seattle next year, centers on a claim that researchers at one company used confidential information from a paper one of the researchers reviewed for Nature in their own research. The trial—if it takes place—could focus on what rules govern the use of information in papers that are sent out for peer review.
Novel Center Seeks to Add Spark to Origins of Life
Authors: Cohen Jon
Published: October 2006

La Jolla, California—The National Aeronautics and Space Administration has been providing $1 million a year for an unusual center focused on studies of the origins of life. It consists of five principal investigators at four separate institutions in the San Diego area. The researchers often disagree with each other, but they are cooperating on a wide range of projects. The aim of the center is to build up an intellectual base—especially by encouraging interaction among graduate students—in a field that has few researchers and little funding.Xs
Mantle Melting and Basalt Extraction by Equilibrium Porous Flow
Authors: Lundstrom C. C. , Gill J. , Williams Q. , Perfit M. R.
Published: October 2006

The chemical composition of mid-ocean ridge basalt, the most prevalent magma type on the planet, reflects the melt's continuous reequilibration with the surrounding mantle during porous flow. Models of basalt extraction that account for the observed uranium-series disequilibria on the Juan de Fuca ridge constrain both the abundance of melt beneath ridges (0.1 to 0.2 percent) and the style of mantle melting. Unlike models that incorporate near-fractional melts (dynamic melting), mixing of equilibrium porous flow melts derived from heterogeneous source materials quantitatively explains the uranium-series observations.
Unusually Mild and Selective Hydrocarbon C-H Bond Activation with Positively Charged Iridium(III) Complexes
Authors: Arndtsen Bruce A. , Bergman Robert G.
Published: October 2006

Certain transition metal complexes can react to break normally inert carbon-hydrogen (C-H) bonds, but these metal-based processes typically require photochemistry or elevated temperatures. In addition, most are unselective toward complicated functionalized substrates, which has limited their synthetic usefulness. The cationic iridium complex Cp*(P(CH
3
)
3
)Ir(CH
3
)(ClCH
2
Cl)
+
BAr
f
−
[Cp* = η
5
-C
5
(CH
3
)
5
, BAr
f
= B(3,5-C
6
H
3
(CF
3
)
2
)
4
] can thermally activate methane and terminal alkanes at unprecedentedly mild temperatures (10°C). This complex will also induce C-H activation reactions in various functionalized substrates at ambient temperatures. High steric and electronic selectivity is observed, leading invariably to only one reaction product; the initial C-H activation reaction is typically followed by rapid metal-based rearrangements (that is, functionalization).
Selective Trafficking of KNOTTED1 Homeodomain Protein and Its mRNA Through Plasmodesmata
Authors: Lucas William J. , Bouché-Pillon Sabine , Jackson David P. , Nguyen Lynda , Baker Lucian , Ding Biao , Hake Sarah
Published: October 2006

Plasmodesmata are intercellular organelles in plants that establish cytoplasmic continuity between neighboring cells. Microinjection studies showed that plasmodesmata facilitate the cell-to-cell transport of a plant-encoded transcription factor, KNOTTED1 (KN1). KN1 can also mediate the selective plasmodesmal trafficking of
kn1
sense RNA. The emerging picture of plant development suggests that cell fate is determined at least in part by supracellular controls responding to cellular position as well as lineage. One of the mechanisms that enables the necessary intercellular communication appears to involve transfer of informational molecules (proteins and RNA) through plasmodesmata.
Tobacco MAP Kinase: A Possible Mediator in Wound Signal Transduction Pathways
Authors: Seo S. , Okamoto M. , Seto H. , Ishizuka K. , Sano H. , Ohashi Y.
Published: October 2006

A complementary DNA encoding a mitogen-activated protein (MAP) kinase homolog has been isolated from tobacco plants. Transcripts of the corresponding gene were not observed in healthy tobacco leaves but began to accumulate 1 minute after mechanical wounding. In tobacco plants transformed with the cloned complementary DNA, trans inactivation of the endogenous homologous gene occurred, and both production of wound-induced jasmonic acid and accumulation of wound-inducible gene transcripts were inhibited. In contrast, the levels of salicylic acid and transcripts for pathogen-inducible, acidic pathogenesis-related proteins were increased upon wounding. These results indicate that this MAP kinase is part of the initial response of higher plants to mechanical wounding.
Tissue Plasminogen Activator Induction in Purkinje Neurons After Cerebellar Motor Learning
Authors: Seeds Nicholas W. , Williams Brian L. , Bickford Paula C.
Published: October 2006

The cerebellar cortex is implicated in the learning of complex motor skills. This learning may require synaptic remodeling of Purkinje cell inputs. An extracellular serine protease, tissue plasminogen activator (tPA), is involved in remodeling various nonneural tissues and is associated with developing and regenerating neurons. In situ hybridization showed that expression of tPA messenger RNA was increased in the Purkinje neurons of rats within an hour of their being trained for a complex motor task. Antibody to tPA also showed the induction of tPA protein associated with cerebellar Purkinje cells. Thus, the induction of tPA during motor learning may play a role in activity-dependent synaptic plasticity.
The
white
Gene of
Ceratitis capitata
: A Phenotypic Marker for Germline Transformation
Authors: Zwiebel Laurence J. , Saccone Giuseppe , Zacharopoulou Antigone , Besansky Nora J. , Favia Guido , Collins Frank H. , Louis Christos , Kafatos Fotis C.
Published: October 2006

Reliable germline transformation is required for molecular studies and ultimately for genetic control of economically important insects, such as the Mediterranean fruit fly (medfly)
Ceratitis capitata
. A prerequisite for the establishment and maintenance of transformant lines is selectable or phenotypically dominant markers. To this end, a complementary DNA clone derived from the medfly
white
gene was isolated, which showed substantial similarity to
white
genes in
Drosophila melanogaster
and other Diptera. It is correlated with a spontaneous mutation causing white eyes in the medfly and can be used to restore partial eye color in transgenic
Drosophila
carrying a null mutation in the endogenous
white
gene.
Evolution of Body Size in the Woodrat over the Past 25,000 Years of Climate Change
Authors: Smith Felisa A. , Betancourt Julio L. , Brown James H.
Published: October 2006

Microevolutionary changes in the body size of the bushy-tailed woodrat (
Neotoma cinerea
) since the last glacial maximum were estimated from measurements of fecal pellets preserved in paleomiddens from the Great Basin and Colorado Plateau of the United States. The changes closely track regional temperature fluctuations simulated by the Community Climate Model of the National Center for Atmospheric Research and also those estimated from deuterium isotope ratios of plant cellulose recovered from paleomiddens. Body size decreased during periods of climatic warming, as predicted from Bergmann's rule and from physiological responses to temperature stress. Fossil woodrat middens, by providing detailed temporal sequences of body sizes from many locations, permit precise quantification of responses to climatic change that have occurred in the past and may occur in the future.
Broken Belt Sets Back New Accelerator
Authors: Hellemans Alexander
Published: October 2006

The Vivitron, a new electrostatic accelerator in Strasbourg, France, that is one of Europe's top facilities for nuclear structure research, has been shut down for 9 months because of difficulties in replacing a rubber-coated fabric belt. The hiatus has delayed an Anglo-French project to study superdeformed nuclei. The Vivitron's managers are confident, however, that they have solved the problem and that the machine will soon be up and running with a newly designed belt that was installed last month.
Obesity: Leptin Receptor Weighs In
Authors: Barinaga Marcia
Published: October 2006

The biggest news in obesity research over the past year has been “the fat gene”: the gene for leptin, a protein that controls body weight in mice. And 1996 is starting off with news that may be just as big. Last week, a research team reported they have cloned DNA that encodes two related receptors that bind the leptin protein in humans and mice, and which may mediate leptin's effects in the body.
A Second Breast Cancer Susceptibility Gene Is Found
Authors: Marx Jean
Published: October 2006

A multinational team of researchers has now added a second breast cancer susceptibility gene, called
BRCA2
, to the one found 15 months ago and known as
BRCA1
. Together, mutations in the two genes account for most of the roughly 10% of breast cancers that are inherited, and the hope is that having this second gene will lead to better screening tests for the cancer-causing mutations, as well as a better understanding of how breast cancer develops.
Flexing Muscle With Just One Amino Acid
Authors: Service Robert F.
Published: October 2006

A key player in muscle contraction is the protein troponin-C, whose contortions after binding calcium ions set off a cell's contraction. Now researchers have demonstrated that those contortions are produced by a single glutamic acid in the protein, which is attracted to the calcium and pulls part of the protein along with it. The result is the first to suggest that a large shape change in a protein can be controlled by just one amino acid.
Stardust in the Laboratory
Authors: Zinner Ernst
Published: October 2006

The isotopic composition of stardust, the matter created as stars burn, is a rich source of information about stellar evolution, synthesis of elements, and solar system formation. In his Perspective, Zinner reviews recent work on the laboratory analysis of stardust preserved in micrometeorites presented at the 58th Meteoritical Society Meeting.
Optical Rockets
Authors: Voss David
Published: October 2006

A research group at the University of Michigan has recently discovered that intense laser pulses called optical rockets can travel along plasma channels for distances of up to 20 meters. In his Perspective, Voss discusses the technology behind the experiment and a possible explanation for the results.
Achieving Linear Scaling for the Electronic Quantum Coulomb Problem
Authors: Strain Matthew C. , Scuseria Gustavo E. , Frisch Michael J.
Published: October 2006

The computation of the electron-electron Coulomb interaction is one of the limiting factors in ab initio electronic structure calculations. The computational requirements for calculating the Coulomb term with commonly used analytic integration techniques between Gaussian functions prohibit electronic structure calculations of large molecules and other nanosystems. Here, it is shown that a generalization of the fast multipole method to Gaussian charge distributions dramatically reduces the computational requirements of the electronic quantum Coulomb problem. Benchmark calculations on graphitic sheets containing more than 400 atoms show near linear scaling together with high speed and accuracy.
Control of Aragonite or Calcite Polymorphism by Mollusk Shell Macromolecules
Authors: Falini Giuseppe , Albeck Shira , Weiner Steve , Addadi Lia
Published: October 2006

Many mineralizing organisms selectively form either calcite or aragonite, two polymorphs of calcium carbonate with very similar crystalline structures. Understanding how these organisms achieve this control has represented a major challenge in the field of biomineralization. Macromolecules extracted from the aragonitic shell layers of some mollusks induced aragonite formation in vitro when preadsorbed on a substrate of β-chitin and silk fibroin. Macromolecules from calcitic shell layers induced mainly calcite formation under the same conditions. The results suggest that these macromolecules are responsible for the precipitation of either aragonite or calcite in vivo.
Sexual Selection for Male Sacrifice in the Australian Redback Spider
Authors: Andrade Maydianne C. B.
Published: October 2006

During copulation, male redback spiders (
Latrodectus hasselti
: Theridiidae) position themselves above the female's jaws. This apparent male complicity in sexual cannibalism is favored by sexual selection because cannibalized spiders receive two paternity advantages. First, cannibalized males copulated longer and fertilized more eggs than those that survived copulation. Second, females were more likely to reject subsequent suitors after consuming their first mate. These results represent empirical evidence for male copulatory suicide as an adaptive behavior.
Direct Observation of Protein Solvation and Discrete Disorder with Experimental Crystallographic Phases
Authors: Burling F. Temple , Weis William I. , Flaherty Kevin M. , Brünger Axel T.
Published: October 2006

A complete and accurate set of experimental crystallographic phases to a resolution of 1.8 angstroms was obtained for a 230-residue dimeric fragment of rat mannose-binding protein A with the use of multiwavelength anomalous dispersion (MAD) phasing. An accurate image of the crystal structure could thus be obtained without resort to phases calculated from a model. Partially reduced disulfide bonds, local disorder, and differences in the mobility of chemically equivalent molecules are apparent in the experimental electron density map. A solvation layer is visible that includes well-ordered sites of hydration around polar and charged protein atoms, as well as diffuse, partially disordered solvent shells around exposed hydrophobic groups. Because the experimental phases and the resulting electron density map are free from the influence of a model, they provide a stringent test of theoretical models of macromolecular solvation, motion, and conformational heterogeneity.
Cancer Charity Falls Afoul of Audit Court
Authors: Nundy Julian
Published: October 2006

Paris—A leaked report on the finances of the Cancer Research Association (ARC), one of France's best known charities and a major funder of cancer research, has thrown the future of the organization into doubt. The report, by the Cour des Comptes, a state auditing agency, is said to conclude that ARC spends less than one third of its income on research, and that there may have been financial mismanagement. ARC has said the real figure is 45%. ARC's board has reduced the power of the charity's influential president, Jacques Crozemarie, and has appointed a commission to run ARC while it prepares a response to the charges. Crozemarie has said that ARC may wind up as an independent charity.