bluuebunny/crossref_metadata_2025 huggingface dataset:
Switching from Cut-and-Paste to Replicative Tn7 Transposition
Authors: May Earl W. , Craig Nancy L.
Published: October 2006

The bacterial transposon Tn7 usually moves through a cut-and-paste mechanism whereby the transposon is excised from a donor site and joined to a target site to form a simple insertion. The transposon was converted to a replicative element that generated plasmid fusions in vitro and cointegrate products in vivo. This switch was a consequence of the separation of 5′- and 3′-end processing reactions of Tn7 transposition as demonstrated by the consequences of a single amino acid alteration in an element-encoded protein essential for normal cut-and-paste transposition. The mutation specifically blocked cleavage of the 5′ strand at each transposon end without disturbing the breakage and joining on the 3′ strand, producing a fusion (the Shapiro Intermediate) that resulted in replicative transposition. The ability of Tn7 recombination products to serve as substrates for both the limited gap repair required to complete cut-and-paste transposition and the extensive DNA replication involved in cointegrate formation suggests a remarkable plasticity in Tn7′s recruitment of host repair and replication functions.
Fluorescent Hydroxyl Emissions from Saturn's Ring Atmosphere
Authors: Hall Doyle T. , Feldman Paul D. , Holberg J. B. , McGrath Melissa A.
Published: October 2006

Just before Earth passed through Saturn's ring plane on 10 August 1995, the Hubble Space Telescope Faint Object Spectrograph detected ultraviolet fluorescent emissions from a tenuous atmosphere of OH molecules enveloping the rings. Brightnesses decrease with increasing distance above the rings, implying a scale height of about 0.45 Saturn radii (
R
S
). A spatial scan 0.28
R
S
above the A and B rings indicates OH column densities of about 10
13
cm
−2
and number densities of up to 700 cm
−3
. Saturn's rings must produce roughly 10
25
to 10
29
OH molecules per second to maintain the observed OH distribution.
Mouse Models of Atherosclerosis
Authors: Breslow Jan L.
Published: October 2006

As a species the mouse is highly resistant to atherosclerosis. However, through induced mutations it has been possible to develop lines of mice that are susceptible to this disease. For example, mice that are deficient in apolipoprotein E, a ligand important in lipoprotein clearance, develop atherosclerotic lesions resembling those observed in humans. These lesions are exacerbated when the mice are fed a high-cholesterol, high-fat, Western-type diet. Other promising models are mice that are deficient in the low density lipoprotein receptor and transgenic mice that express human apolipoprotein B and transdominant mutant forms of apolipoprotein E. These models are now being used to study the pathogenesis of atherosclerotic lesions, as well as the influence of genetics, environment, hormones, and drugs on lesion development.
Photoinduced Magnetization of a Cobalt-Iron Cyanide
Authors: Sato O. , Iyoda T. , Fujishima A. , Hashimoto K.
Published: October 2006

Photoinduced magnetization was observed in a Prussian blue analog, K
0.2
Co
1.4
- [Fe(CN)
6
]⋅6.9H
2
O. An increase in the critical temperature from 16 to 19 kelvin was observed as a result of red light illumination. Moreover, the magnetization in the ferrimagnetic region below 16 kelvin was substantially increased after illumination and could be restored almost to its original level by thermal treatment. These effects are thought to be caused by an internal photochemical redox reaction. Furthermore, blue light illumination could be used to partly remove the enhancement of the magnetization. Such control over magnetic properties by optical stimuli may have application in magneto-optical devices.
Galileo Gravity Results and the Internal Structure of Io
Authors: Anderson J. D. , Sjogren W. L. , Schubert G.
Published: October 2006

Doppler data generated with the Galileo spacecraft's radio carrier wave were used to measure Io's external gravitational field. The resulting triaxial field is consistent with the assumption that Io is in tidal and rotational equilibrium. The inescapable conclusion is that it has a large metallic core. If the core is a eutectic mixture of iron and iron sulfide, it comprises 20.2 ± 7.4 percent of the satellite's total mass with a radius that is about 52 percent of Io's mean radius of 1821.3 kilometers; if the core is pure iron, it comprises 10.5 ± 3.7 percent of the total mass with a radius of about 36 percent of the mean radius.
Juvenile Skeletal Structure and the Reproductive Habits of Dinosaurs
Authors: Geist Nicholas R. , Jones Terry D.
Published: October 2006

Skeletal ontogeny in extant archosaurians (crocodilians and birds) indicates that the morphology of the perinatal pelvic girdle is an indicator of overall developmental maturity [that is, altriciality (nestbound) versus precociality (mobile and relatively independent)]. Comparison of the skeletal anatomy of perinatal extant archosaurians and perinatal dinosaurs suggests that known dinosaur hatchlings were precocial. These data are consistent with the overall similarity in nesting behavior of dinosaurs and modern crocodilians.
Cell Growth Arrest and Induction of Cyclin-Dependent Kinase Inhibitor p21
WAF1/CIP1
Mediated by STAT1
Authors: Chin Yue E. , Kitagawa Motoo , Su Wu-Chou S. , You Zhi-Hao , Iwamoto Yoshiki , Fu Xin-Yuan
Published: October 2006

Signal transducers and activators of transcription (STAT) proteins can be conditionally activated in response to epidermal growth factor (EGF) and interferon (IFN)-γ. STAT activation was correlated with cell growth inhibition in response to EGF and IFN-γ. Activated STAT proteins specifically recognized the conserved STAT-responsive elements in the promoter of the gene encoding the cyclin-dependent kinase (CDK) inhibitor p21
WAF1/CIP1
and regulated the induction of p21 messenger RNA. IFN-γ did not inhibit the growth of U3A cells, which are deficient in STAT1, but did inhibit the growth of U3A cells into which STAT1α was reintroduced. Thus, STAT1 protein is essential for cell growth suppression in response to IFN-γ. The STAT signaling pathway appears to negatively regulate the cell cycle by inducing CDK inhibitors in response to cytokines.
Goldin Puts NASA on New Trajectory
Authors: Lawler Andrew
Published: October 2006

Keen political instincts, stamina, and a ruthless management style have helped Dan Goldin lead a revolution at this once-placid space agency. But now Goldin faces his biggest challenge—doing faster, cheaper, and better science with a shrinking budget that contains several politically untouchable programs. Is he up to the task? “I won't give up,” he promises.
Monkey Study Prompts High-Level Public Health Response
Authors: Cohen Jon
Published: October 2006

A finding that monkeys treated with the hormone progesterone are at an increased risk of infection with SIV, the simian form of the AIDS virus, caused top public health officials to scramble to get the data out with the appropriate caveats. The reason: The finding raises the alarming possibility that women who use the progestin-containing contraceptives Depo-Provera and Norplant might—and that's a big might—be at an increased risk of becoming infected with HIV. The data were described at a meeting in Washington this week, accompanied by a press release, even before a paper describing the work had been accepted for publication.
Just How Old Is That DNA, Anyway?
Authors: Service Robert F.
Published: October 2006

A handful of research groups have reported recovering DNA from insects trapped in amber and even dinosaurs entombed in coal—samples as old as 135 million years. But skeptics have shot back that intact DNA from old sources is more likely to be from some modern interloper in the sample, such as bacteria. Now researchers have an independent test of ancient DNA authenticity. On (
page 864
), an international team reports that a chemical change that converts amino acids in proteins from one mirror-image form to another—a process known as racemization—takes place at virtually the same rate as the degradation of DNA. If amino acids in a sample show this conversion to even a modest degree, original DNA is likely long gone. Any remaining genetic material should be a contaminant. When the researchers used this test on a variety of ancient DNA samples, they found that only those from insects trapped in amber appear to stand the test of time.
The Helium Mass Fraction in Jupiter's Atmosphere
Authors: von Zahn U. , Hunten D. M.
Published: October 2006

On 7 December 1995, the NASA Galileo probe provided in situ measurements of the helium abundance in the atmosphere of Jupiter. A Jamin interferometer measured the refractive index of the jovian atmosphere in the pressure region from 2 to 14 bars. These measurements indicate that the atmospheric helium mole fraction is 0.136 ± 0.004. The corresponding helium mass fraction is slightly below the presolar value, which suggests that separation of helium from hydrogen in Jupiter's interior is only in its early stages.
Osmium Recycling in Subduction Zones
Authors: Brandon Alan D. , Creaser Robert A. , Shirey Steven B. , Carlson Richard W.
Published: October 2006

Peridotite xenoliths from the Cascade arc in the United States and in the Japan arc have neodymium and osmium isotopic compositions that are consistent with addition of 5 to 15 percent of subducted material to the present-day depleted mantle. These observations suggest that osmium can be partitioned into oxidized and chlorine-rich slab-derived fluids or melts. These results place new constraints on the behavior of osmium (and possibly other platinum group elements) during subduction of oceanic crust by showing that osmium can be transported into the mantle wedge.
Structures of an MHC Class II Molecule with Covalently Bound Single Peptides
Authors: Fremont Daved H. , Hendrickson Wayne A. , Marrack Philippa , Kappler John
Published: October 2006

The high-resolution x-ray crystal structures of the murine major histocompatibility complex (MHC) class II molecule, I-E
k
, occupied by either of two antigenic peptides were determined. They reveal the structural basis for the I-E
k
peptide binding motif and suggest general principles for additional alleles. A buried cluster of acidic amino acids in the binding groove predicted to be conserved among all murine I-E and human DR MHC class II molecules suggests how pH may influence MHC binding or exchange of peptides. These structures also complement mutational studies on the importance of individual peptide residues to T cell receptor recognition.
The Role of Zinc in Selective Neuronal Death After Transient Global Cerebral Ischemia
Authors: Koh Jae-Young , Suh Sang W. , Gwag Byoung J. , He Yong Y. , Hsu Chung Y. , Choi Dennis W.
Published: October 2006

Zinc is present in presynaptic nerve terminals throughout the mammalian central nervous system and likely serves as an endogenous signaling substance. However, excessive exposure to extracellular zinc can damage central neurons. After transient forebrain ischemia in rats, chelatable zinc accumulated specifically in degenerating neurons in the hippocampal hilus and CA1, as well as in the cerebral cortex, thalamus, striatum, and amygdala. This accumulation preceded neurodegeneration, which could be prevented by the intraventricular injection of a zinc chelating agent. The toxic influx of zinc may be a key mechanism underlying selective neuronal death after transient global ischemic insults.
House Panel Wants Bigger Bang for Buck
Authors: Mervis Jeffrey
Published: October 2006

The growing scale of the Small Business Innovation Research (SBIR) program has led Congress to consider a provision to tailor the Department of Defense's half-billion dollar investment—the largest amount spent by any agency—more closely to the military's needs. The concern is that the program is more likely to generate “gee-whiz” technology than to give troops an edge on the battlefield.
A Glow From the First Galaxies?
Authors: Watson Andrew
Published: October 2006

A joint French-Dutch team may have uncovered a faint reddish glow from the cosmos's first generation of galaxies. These galaxies, too faint and distant to be seen directly, would have been shrouded in dust, which would have reradiated their light at infrared wavelengths. By carefully stripping away foreground sources of infrared radiation from data collected by the COBE satellite, the team found a uniform residual signal that it tentatively identified as this primordial glow. But because of the difficulty of this procedure, other astrophysicists are reserving judgment.
Hong Kong's Pre-1997 Science Boom
Authors: Kinoshita June
Published: October 2006

Hong Kong—The upcoming transfer of control to China has made the British colony a magnet for researchers looking for economic and scientific links to the mainland. A heavy investment in new facilities, research funds, computer networks, and personnel is nearing critical mass in such fields as mathematics and telecommunications. In contrast, the strategy so far seems not to be working for biotechnology, where the lack of a research base is diluting the impact of a sizable capital investment.
Seeking Life's Bare (Genetic) Necessities
Authors: Pennisi Elizabeth
Published: October 2006

Cold Spring Harbor, New York—At the recent genome meeting here, researchers homed in on a fundamental question: What's the minimum number of genes needed for a simple organism to survive? Two presentations used contrasting approaches and came up with only slightly different estimates. One group found that 250 genes is the minimum for a modern organism, while another team estimated that 800 genes is enough to do the job.
Zebrafish Embryology Builds Better Model Vertebrate
Authors: Roush Wade
Published: October 2006

Highly touted as a model of vertebrate development, the zebrafish has actually worried a number of biologists for some time. Technical obstacles have prevented them from observing whether its tissues develop along typical vertebrate pathways; an odd growth pattern would ruin the fish's value as a model. But a recent series of embryological experiments has brought a rush of relief. Scientists have sidestepped the technical hurdles and revealed that zebrafish develop like most vertebrates do. In the future, the techniques can be combined with the many zebrafish mutations to bring genetics and embryology together, showing how genes affect the where and when of tissue development with unparalleled precision
Viral Counts Count in HIV Infection
Authors: Ho David D.
Published: October 2006

A single measurement of the amount of the human immunodeficiency virus (HIV) in a patient's blood can predict the subsequent risk of acquired immunodeficiency syndrome (AIDS) or death, even before the patient shows signs of the disease—so reports a paper (Mellors
et al
.,
p.1167
) in this issue. In his Perspective, Ho discusses why this is the case and why measurement of viral loads will become extremely useful clinically.
Oceanic Anoxia and the End Permian Mass Extinction
Authors: Wignall Paul B. , Twitchett Richard J.
Published: October 2006

Data on rocks from Spitsbergen and the equatorial sections of Italy and Slovenia indicate that the world's oceans became anoxic at both low and high paleolatitudes in the Late Permian. Such conditions may have been responsible for the mass extinction at this time. This event affected a wide range of shelf depths and extended into shallow water well above the storm wave base.
GS28, a 28-Kilodalton Golgi SNARE That Participates in ER-Golgi Transport
Authors: Subramaniam V. Nathan , Peter Frank , Philp Robin , Wong Siew Heng , Hong Wanjin
Published: October 2006

Little is known about the integral membrane proteins that participate in the early secretory pathway of mammalian cells. The complementary DNA encoding a 28-kilodalton protein (p28) of the cis-Golgi was cloned and sequenced. The protein was predicted to contain a central coiled-coil domain with a carboxyl-terminal membrane anchor. An in vitro assay for endoplasmic reticulum-Golgi transport was used to show that p28 participates in the docking and fusion stage of this transport event. Biochemical studies established that p28 is a core component of the Golgi SNAP receptor (SNARE) complex.
Vertical Flux of Biogenic Carbon in the Ocean: Is There Food Web Control?
Authors: Rivkin Richard B. , Legendre Louis , Deibel Don , Tremblay Jean-Éric , Klein Bert , Crocker Kenneth , Roy Suzanne , Silverberg Norman , Lovejoy Connie , Mesplé Fabrice , Romero Nancy , Anderson M. Robin , Matthews Paul , Savenkoff Claude , Vézina Alain , Therriault Jean-Claude , Wesson Joel , Bérubé Chantal , Ingram R. Grant
Published: October 2006

Models of biogenic carbon (BC) flux assume that short herbivorous food chains lead to high export, whereas complex microbial or omnivorous food webs lead to recycling and low export, and that export of BC from the euphotic zone equals new production (NP). In the Gulf of St. Lawrence, particulate organic carbon fluxes were similar during the spring phytoplankton bloom, when herbivory dominated, and during nonbloom conditions, when microbial and omnivorous food webs dominated. In contrast, NP was 1.2 to 161 times greater during the bloom than after it. Thus, neither food web structure nor NP can predict the magnitude or patterns of BC export, particularly on time scales over which the ocean is in nonequilibrium conditions.
Direct Regulation of ZAP-70 by SHP-1 in T Cell Antigen Receptor Signaling
Authors: Plas David R. , Johnson Robin , Pingel Jeanette T. , Matthews R. James , Dalton Mark , Roy Garbiñe , Chan Andrew C. , Thomas Matthew L.
Published: October 2006

The threshold at which antigen triggers lymphocyte activation is set by the enzymes that regulate tyrosine phosphorylation. Upon T cell activation, the protein tyrosine phosphatase SHP-1 was found to bind to the protein tyrosine kinase ZAP-70. This interaction resulted in an increase in SHP-1 phosphatase activity and a decrease in ZAP-70 kinase activity. Expression of a dominant negative mutant of SHP-1 in T cells increased the sensitivity of the antigen receptor. Thus, SHP-1 functions as a negative regulator of the T cell antigen receptor and in setting the threshold of activation.
Polyclonal Origin of Colonic Adenomas in an XO/XY Patient with FAP
Authors: Novelli M. R. , Williamson J. A. , Tomlinson I. P. M. , Elia G. , Hodgson S. V. , Talbot I. C. , Bodmer W. F. , Wright N. A.
Published: October 2006

It is widely accepted that tumors are monoclonal in origin, arising from a mutation or series of mutations in a single cell and its descendants. The clonal origin of colonic adenomas and uninvolved intestinal mucosa from an XO/XY mosaic individual with familial adenomatous polyposis (FAP) was examined directly by in situ hybridization with Y chromosome probes. In this patient, the crypts of the small and large intestine were clonal, but at least 76 percent of the microadenomas were polyclonal in origin.
Infertility Treatment: A Nuclear Restorer Gene in Maize
Authors: Levings Charles S.
Published: October 2006

A sterile strain of corn that has been used for making hybrid seed corn carries the Texas male-sterile cytoplasm and does not make pollen. In a report in this issue of
Science
(see Cui
et al
.,
page 1334
), cloning of a gene that can restore fertility to these plants is announced. In his Perspective, Levings discussed why the identification of this gene
Rf2
as an aldehyde dehydrogenase is surprising and how it may work to reverse the male sterile phenotype.
GONG Observations of Solar Surface Flows
Authors: Hathaway D. H. , Gilman P. A. , Harvey J. W. , Hill F. , Howard R. F. , Jones H. P. , Kasher J. C. , Leibacher J. W. , Pintar J. A. , Simon G. W.
Published: October 2006

Doppler velocity observations obtained by the Global Oscillation Network Group (GONG) instruments directly measure the nearly steady flows in the solar photosphere. The sun's differential rotation is accurately determined from single observations. The rotation profile with respect to latitude agrees well with previous measures, but it also shows a slight north-south asymmetry. Rotation profiles averaged over 27-day rotations of the sun reveal the torsional oscillation signal—weak, jetlike features, with amplitudes of 5 meters per second, that are associated with the sunspot latitude activity belts. A meridional circulation with a poleward flow of about 20 meters per second is also evident. Several characteristics of the surface flows suggest the presence of large convection cells.
Filled Skutterudite Antimonides: A New Class of Thermoelectric Materials
Authors: Sales B. C. , Mandrus D. , Williams R. K.
Published: October 2006

A class of thermoelectric materials has been synthesized with a thermoelectric figure of merit
ZT
(where
T
is temperature and
Z
is a function of thermopower, electrical resistivity, and thermal conductivity) near 1 at 800 kelvin. Although these materials have not been optimized, this value is comparable to the best
ZT
values obtained for any previously studied thermoelectric material. Calculations indicate that the optimized material should have
ZT
values of 1.4. These ternary semiconductors have the general formula RM
4
X
12
(where R is lanthanum, cerium, praseodymium, neodymium, or europium; M is iron, ruthenium, or osmium; and X is phosphorus, arsenic, or antimony) and represent a new approach to creating improved thermoelectric materials. Several alloys in the composition range CeFe

4−
x

Co

x

Sb
12
or LaFe

4−
x

Co

x

Sb
12
(0 <
x
< 4) have large values of
ZT
.
Movie Captures Dance of the Crab
Authors: Peterson Kim
Published: October 2006

Over the past year, astronomers used NASA's Hubble Space Telescope to make time-lapse images of the Crab Nebula, the relic of a supernova explosion 7000 light-years away. The result is a movie that reveals week-by-week changes in the glowing gases and shows that the spinning neutron star at the heart of the nebula doesn't fling out particles uniformly, as was thought, but in two specific regions. Waves of material emanate from its equatorial regions, and a focused jet spurts from its south pole. Now theorists have to figure out why
A New Turn (or Two) for Twist
Authors: Michelson Alan M.
Published: October 2006

Two reports in this week's issue of
Science
[Baylies (
p. 1481
) and Spicer (
p. 1476
)] describe new functions in muscle development for the gene
twist
, a basic helix-loop-helix transcription factor. In his Perspective, Michelson explains how these two seemingly contradictory functions of
twist
(specification of mesodermal cell fate in fruit flies and inhibition of muscle differentiation in vertebrates) can be reconciled.
Regulation of the Inositol 1,4,5-Trisphosphate Receptor by Tyrosine Phosphorylation
Authors: Jayaraman Thottala , Ondrias Karol , Ondria Elenaová , Marks Andrew R.
Published: October 2006

Tyrosine kinases indirectly raise intracellular calcium concentration ([Ca
2+
]
i
) by activating phospholipases that generate inositol 1,4,5-trisphosphate (IP
3
). IP
3
activates the IP
3
receptor (IP
3
R), an intracellular calcium release channel on the endoplasmic reticulum. T cell receptor stimulation triggered a physical association between the nonreceptor protein tyrosine kinase Fyn and the IP
3
R, which induced tyrosine phosphorylation of the IP
3
R. Fyn activated an IP
3
-gated calcium channel in vitro, and tyrosine phosphorylation of the IP
3
R during T cell activation was reduced in thymocytes from
fyn
−/−
mice. Thus, activation of the IP
3
R by tyrosine phosphorylation may play a role in regulating [Ca
2+
]
i
.
Is Evolution Enough?
Authors: Lawler Andrew
Published: October 2006

The Department of Energy's (DOE's) $8-billion-a-year network of laboratories is scrambling to survive budget cuts and political pressure to define missions. Ironically, the financial pressures come at a time when new facilities are providing researchers with unprecedented scientific opportunities. Can the labs reinvent themselves in time? A 2-day “war game” suggests it will be hard to head off a lab-closing commission.
Ice Bubbles Confirm Big Chill
Authors: Kerr Richard A.
Published: October 2006

Clues in Greenland's ice sheet have shown that during the last ice age its climate repeatedly warmed sharply, only to slide into a renewed chill lasting thousands of years. Just how drastic the warmings and coolings were and how widely they were felt has been a matter of debate, but new indicators derived not from the ice itself but from trapped bubbles of ancient gases—nitrogen and methane—have confirmed the severity of the last of these climate swings. Known as the Younger Dryas, this cold snap 12,000 years ago brought temperatures 14 degrees Celsius colder than today to Greenland, and it affected much of the world.
Precocious Structures Found
Authors: Glanz James
Published: October 2006

In the nearby universe, gravity has organized galaxies into great walls, voids, and filaments, and many cosmologists believe these structures are latecomers to the cosmos. But new observations made by a Caltech team with the Keck 10-meter telescope in Hawaii suggest that wall-like structures may have already been common in the universe billions of years ago. If the findings hold up, theorists may have to revise ideas about the density and makeup of the universe.
Crystal Structure of DMSO Reductase: Redox-Linked Changes in Molybdopterin Coordination
Authors: Schindelin Hermann , Kisker Caroline , Hilton James , Rajagopalan K. V. , Rees Douglas C.
Published: October 2006

The molybdoenzyme dimethylsulfoxide (DMSO) reductase contributes to the release of dimethylsulfide, a compound that has been implicated in cloud nucleation and global climate regulation. The crystal structure of DMSO reductase from
Rhodobacter sphaeroides
reveals a monooxo molybdenum cofactor containing two molybdopterin guanine dinucleotides that asymmetrically coordinate the molybdenum through their dithiolene groups. One of the pterins exhibits different coordination modes to the molybdenum between the oxidized and reduced states, whereas the side chain oxygen of Ser
147
coordinates the metal in both states. The change in pterin coordination between the Mo(VI) and Mo(IV) forms suggests a mechanism for substrate binding and reduction by this enzyme. Sequence comparisons of DMSO reductase with a family of bacterial oxotransferases containing molybdopterin guanine dinucleotide indicate a similar polypeptide fold and active site with two molybdopterins within this family.
Microscopic Particle Motions in Strongly Coupled Dusty Plasmas
Authors: I Lin , Juan Wen-Tau , Chiang Chih-Hui , Chu J. H.
Published: October 2006

The microscopic particle motions from the crystal to the disordered state of a dusty plasma with micrometer-sized silicon dioxide particle suspensions in a radio-frequency glow discharge system were studied through an optical microimaging system. Small-amplitude random motion around the lattice sites of the crystal state, relative domain motion with varying boundaries, cooperative hopping in the liquid state, and highly disordered motion with increasing radio-frequency power were observed. Chaotic states with different spatial scales under the coherent and stochastic coupling between dust particles and self-organized background plasma fluctuations were also demonstrated.
Climate Change During the Last Deglaciation in Antarctica
Authors: Mayewski P. A. , Twickler M. S. , Whitlow S. I. , Meeker L. D. , Yang Q. , Thomas J. , Kreutz K. , Grootes P. M. , Morse D. L. , Steig E. J. , Waddington E. D. , Saltzman E. S. , Whung P.-Y. , Taylor K. C.
Published: October 2006

Greenland ice core records provide clear evidence of rapid changes in climate in a variety of climate indicators. In this work, rapid climate change events in the Northern and Southern hemispheres are compared on the basis of an examination of changes in atmospheric circulation developed from two ice cores. High-resolution glaciochemical series, covering the period 10,000 to 16,000 years ago, from a central Greenland ice core and a new site in east Antarctica display similar variability. These findings suggest that rapid climate change events occur more frequently in Antarctica than previously demonstrated.
Chipping Away at the Human Genome
Authors: Pennisi Elizabeth
Published: October 2006

Eric Lander of the Whitehead Institute in Cambridge, Massachusetts, is legendary for presenting dazzling new technologies at the annual genome meeting at Cold Spring Harbor Laboratory in New York, and last month's 1996 gathering was no exception. Lander unveiled applications for a “DNA chip,” developed by Affymetrix, a biotechnology company in Santa Clara, California. Built with the same techniques as computer chips, the DNA chip holds thousands of tailor-made stretches of DNA. And although its first use will be in evaluating markers for genetic mapping, the chip could one day be a versatile tool for rapidly scanning entire genomes.
A Second Coreceptor for HIV in Early Stages of Infection
Authors: Balter Michael
Published: October 2006

Two papers published in this week's issue of
Nature
and a third that will appear in the 28 June issue of
Science
(with independent results from at least one other team reportedly about to be published) report the identification of an essential “coreceptor” for the HIV strains involved in the critical early stages of infection. All have fingered a cell membrane-bound protein called CC-CKR-5 as the elusive partner of HIV's primary receptor, CD4, in allowing these strains to enter their target cells. Last month, another coreceptor, called “fusin,” was reported in
Science
(10 May, p. 809). The discovery of these two coreceptors--and perhaps others yet to be identified--suggests that HIV may use different molecules to enter the cell at different stages of the disease.
New Solar Cells Seem to Have Power at the Right Price
Authors: Service Robert F.
Published: October 2006

Efficiency versus cost. It's a trade-off that bedevils makers of solar cells. Cells made from crystalline silicon are good at absorbing photons and converting them to electricity. But they cost a lot. In contrast, noncrystalline cells made with amorphous silicon are much cheaper—but only about half as efficient as their crystalline counterparts. Now researchers think that they can trade in this devilish trade-off. At a conference last month in Arlington, Virginia, scientists were energized by a report that an ultrathin film—a mixture of copper, indium, gallium, and selenium—has been made into prototype cells that convert nearly 18% of incoming photons to electricity, a performance approaching that of the best crystalline silicon cells. If researchers can overcome nagging manufacturing and marketing problems, new devices could produce power for less than $0.50 per watt.
Nanoscale Magnetic Domains in Mesoscopic Magnets
Authors: Hehn Michel , Ounadjela Kamel , Bucher Jean-Pierre , Rousseaux Françoise , Decanini Dominique , Bartenlian Bernard , Chappert Claude
Published: October 2006

The basic magnetic properties of three-dimensional nanostructured materials can be drastically different from those of a continuous film. High-resolution magnetic force microscopy studies of magnetic submicrometer-sized cobalt dots with geometrical dimensions comparable to the width of magnetic domains reveal a variety of intricate domain patterns controlled by the details of the dot geometry. By changing the thickness of the dots, the width of the geometrically constrained magnetic domains can be tuned. Concentric rings and spirals with vortex configurations have been stabilized, with particular incidence in the magnetization reversal process as observed in the ensemble-averaged hysteresis loops.
Neural Substrates for the Effects of Rehabilitative Training on Motor Recovery After Ischemic Infarct
Authors: Nudo Randolph J. , Wise Birute M. , SiFuentes Frank , Milliken Garrett W.
Published: October 2006

Substantial functional reorganization takes place in the motor cortex of adult primates after a focal ischemic infarct, as might occur in stroke. A subtotal lesion confined to a small portion of the representation of one hand was previously shown to result in a further loss of hand territory in the adjacent, undamaged cortex of adult squirrel monkeys. In the present study, retraining of skilled hand use after similar infarcts resulted in prevention of the loss of hand territory adjacent to the infarct. In some instances, the hand representations expanded into regions formerly occupied by representations of the elbow and shoulder. Functional reorganization in the undamaged motor cortex was accompanied by behavioral recovery of skilled hand function. These results suggest that, after local damage to the motor cortex, rehabilitative training can shape subsequent reorganization in the adjacent intact cortex, and that the undamaged motor cortex may play an important role in motor recovery.
Corn: A Lot of Change From a Little DNA
Authors: Roush Wade
Published: October 2006

Nashville, Tennessee—Corn may be the domesticated version of the bushy and inedible weed called teosinte, but you wouldn't know it to look at the two plants. Corn ears, for instance, are covered with hundreds of soft, edible kernels, while teosinte flowers are studded with just a dozen or so, all firmly encased in armor. At the national meeting of the Society for Developmental Biology here 3 weeks ago, however, scientists reported that the change from inedible to edible could come from mutations in just one small stretch of teosinte DNA. Not only does the work support the growing notion that minor genetic changes can result in large evolutionary leaps, but researchers suggest it may even point toward a way of engineering similar improvements in other cereal or grain plants.
Eradicating HIV From a Patient: Not Just a Dream?
Authors: Pennisi Elizabeth , Cohen Jon
Published: October 2006

A new understanding of HIV pathogenesis that has emerged over the past 18 months has led AIDS researchers to pose what was recently an unthinkable question: Can HIV be eradicated from an infected person? A conference in Washington, D.C., 2 weeks ago, which focused on just that question, indicated that many researchers are now thinking the unthinkable.
Minimal Energy Requirements in Communication
Authors: Landauer Rolf
Published: October 2006

The literature describing the energy needs for a communications channel has been dominated by analyses of linear electromagnetic transmission, often without awareness that this is a special case. This case leads to the conclusion that an amount of energy equal to
kT
ln 2, where
kT
is the thermal noise per unit bandwidth, is needed to transmit a bit, and more if quantized channels are used with photon energies
h
ν >
kT
. Alternative communication methods are proposed to show that there is no unavoidable minimal energy requirement per transmitted bit. These methods are invoked as part of an analysis of ultimate limits and not as practical procedures.
Solution Structure of a Two-Base DNA Bulge Complexed with an Enediyne Cleaving Analog
Authors: Stassinopoulos Adonis , Ji Jie , Gao Xiaolian , Goldberg Irving H.
Published: October 2006

Nucleic acid bulges have been implicated in a number of biological processes and are specific cleavage targets for the enediyne antitumor antibiotic neocarzinostatin chromophore in a base-catalyzed, radical-mediated reaction. The solution structure of the complex between an analog of the bulge-specific cleaving species and an oligodeoxynucleotide containing a two-base bulge was elucidated by nuclear magnetic resonance. An unusual binding mode involves major groove recognition by the drug carbohydrate unit and tight fitting of the wedge-shaped drug in the triangular prism pocket formed by the two looped-out bulge bases and the neighboring base pairs. The two drug rings mimic helical DNA bases, complementing the bent DNA structure. The putative abstracting drug radical is 2.2 ± 0.1 angstroms from the pro-
S
H5′ of the target bulge nucleotide. This structure clarifies the mechanism of bulge recognition and cleavage by a drug and provides insight into the design of bulge-specific nucleic acid binding molecules.
Chauvet Study Gets the Go-Ahead
Authors: Balter Michael
Published: October 2006

Paris—Earlier this month, France's Ministry of Culture awarded archaeologist Jean Clottes a once-in-a-lifetime opportunity: He was chosen to direct research at the Grotte Chauvet in southern France, recently discovered site of the world's oldest known cave paintings. This is not surprising perhaps, as Clottes is the culture ministry's own scientific adviser on prehistoric art and one of the world's leading authorities in the field. But Clottes was not handed the job on a plate: He had to compete for the right to study the cave against another French team and had to endure legal wrangles over rights to photographs taken of the cave paintings and compensation for the owners of the land the cave was found on.
Agencies Scramble to Measure Public Impact of Research
Authors: Mervis Jeffrey
Published: October 2006

Federal research agencies are looking for ways to quantify their performance under a 1993 law aimed at making sure taxpayers get the most for their money. Officials are already beginning to tie their budget requests to the goals that their agency has set, but the hard part is coming up with metrics to chart their progress. Next week Congress will hear from six agencies in its first close look at how the law will affect the federal government's $70 billion research portfolio.
Folding Proteins Caught in the Act
Authors: Service Robert F.
Published: October 2006

Proteins are master shape-shifters, twisting rapidly from a plain ribbon of amino acids into the contorted helices they prefer. The earliest stages of this process happen so fast that until recently, no one has been able to observe them. Now biochemists have developed new techniques to coax proteins to fold on a hair trigger and to snap freeze-frame images of the folding process. Such methods will eventually offer clues to the rules behind the folding process.
Sky-High Findings Drop New Hints of Greenhouse Warming
Authors: Kerr Richard A.
Published: October 2006

Last December, an international body of scientists officially concluded that humans are indeed affecting global climate, a judgment based in part on research that picked out the distinctive signal of human-induced change in surface temperature patterns. Industry groups have recently challenged the report, but new data on temperatures higher in the atmosphere support the original conclusion. Work published in this week's issue of
Nature
shows that the pattern of recent atmospheric temperature changes matches that predicted by computer models of greenhouse warming.
Helical Beams Give Particles a Whirl
Authors: Bains Sunny
Published: October 2006

For the past 25 years, physicists wanting to pick up and hold particles as small as a single molecule have used very precise laser beams in setups known as “optical tweezers.” Now two teams of researchers, in the United Kingdom and in Australia, have found that by using specially sculpted laser beams they can do more than just hold a molecule: They can make it spin, speed up and slow down its spinning, and even bring it to a stop and spin it the other way. The researchers say the technique may one day be useful in nanotechnology and, because it requires less power than conventional optical tweezers, can be used to manipulate living biological tissue without killing it.
How T Cells Count
Authors: Rothenberg Ellen V.
Published: October 2006

The rules by which the T cells of the immune system are activated by foreign peptides have seemed inconsistent and counterintuitive. In this week's issue, Viola
et al
. (
p. 104
) report that the T cells actually count how many T cell receptors are engaged. When the number 8000 is reached, the T cell becomes activated. In her Perspective, Rothenberg describes the many questions this discovery resolves.
Protein Matchmaker May Lead New Gene Therapy to the Altar
Authors: Balter Michael
Published: October 2006

An ancient molecular weapon, devised by a lowly bacterium to fight off fungi and other competitors for scarce nutrients, could become one of the newest additions to the arsenal of drug design and gene therapy. On
page 239
, researchers use x-ray crystallography to show that the molecule—rapamycin—plays the role of a marriage broker, linking two proteins that normally ignore each other into a complex, called a heterodimer, that actively interferes with the proliferation of the immune system's T lymphocytes. With a little molecular tinkering, researchers say, that structure might perform other functions. One, already being explored as gene therapy, is to bring together molecular partners that perform specific functions, such as turning off or on cell signaling pathways or specific genes.
New Designs of Macroporous Polymers and Supports: From Separation to Biocatalysis
Authors: Svec Frantisek , Fréchet Jean M. J.
Published: October 2006

Reactive polymers play many roles, from supports for solid-phase synthesis or catalysis to media for separations. Although macroporous polymer beads that provide high reactive capacities and excellent solvent tolerance are well established, approaches to monosized beads with optimized pore structures or multiple chemistries segregated within pores of different sizes have expanded their realm of application. Polymer monoliths containing intricate pore networks can be obtained in any desired shape by a simple molding process and provide unique advantages such as fast kinetics, high reactivity, and high throughput. Applications ranging from immobilized enzyme reactors to fast media for the separation of synthetic or biopolymers are presented.
Polar Overdominance at the Ovine

callipyge

Locus
Authors: Cockett Noelle E. , Jackson Sam P. , Shay Tracy L. , Farnir Frédéric , Berghmans Stéphane , Snowder Gary D. , Nielsen Dahlia M. , Georges Michel
Published: October 2006

An inheritable muscular hypertrophy was recently described in sheep and shown to be determined by the
callipyge
gene mapped to ovine chromosome 18. Here, the callipyge phenotype was found to be characterized by a nonmendelian inheritance pattern, referred to as polar overdominance, where only heterozygous individuals having inherited the
callipyge
mutation from their sire express the phenotype. The possible role of parental imprinting in the determinism of polar overdominance is envisaged.
Structure of the FKBP12-Rapamycin Complex Interacting with Binding Domain of Human FRAP
Authors: Choi Jungwon , Chen Jie , Schreiber Stuart L. , Clardy Jon
Published: October 2006

Rapamycin, a potent immunosuppressive agent, binds two proteins: the FK506-binding protein (FKBP12) and the FKBP-rapamycin-associated protein (FRAP). A crystal structure of the ternary complex of human FKBP12, rapamycin, and the FKBP12-rapamycin-binding (FRB) domain of human FRAP at a resolution of 2.7 angstroms revealed the two proteins bound together as a result of the ability of rapamycin to occupy two different hydrophobic binding pockets simultaneously. The structure shows extensive interactions between rapamycin and both proteins, but fewer interactions between the proteins. The structure of the FRB domain of FRAP clarifies both rapamycin-independent and -dependent effects observed for mutants of FRAP and its homologs in the family of proteins related to the ataxia-telangiectasia mutant gene product, and it illustrates how a small cell-permeable molecule can mediate protein dimerization.
Long-Term Lymphohematopoietic Reconstitution by a Single CD34-Low/Negative Hematopoietic Stem Cell
Authors: Osawa Masatake , Hanada Ken-ichi , Hamada Hirofumi , Nakauchi Hiromitsu
Published: October 2006

Hematopoietic stem cells (HSCs) supply all blood cells throughout life by making use of their self-renewal and multilineage differentiation capabilities. A monoclonal antibody raised to the mouse homolog of CD34 (mCD34) was used to purify mouse HSCs to near homogeneity. Unlike in humans, primitive adult mouse bone marrow HSCs were detected in the mCD34 low to negative fraction. Injection of a single mCD34
lo/−
, c-Kit
+
, Sca-1
+
, lineage markers negative (Lin
−
) cell resulted in long-term reconstitution of the lymphohematopoietic system in 21 percent of recipients. Thus, the purified HSC population should enable analysis of the self-renewal and multilineage differentiation of individual HSCs.
Cuprates Fall into a Gap
Authors: Ong N. P.
Published: October 2006

Superconductors are characterized by an energy gap that is a measure of the robustness of the superconducting state. Recent experimental evidence has indicated the existence of another energy gap at a higher temperature. As discussed in a Perspective by Ong, electron photoemission results reported by Loeser
et al
. in this issue (
p. 325
) provide a clearer picture of this second gap and may allow further discrimination among competing models of high-temperature superconductivity.
Oxygenic Photoautotrophic Growth Without Photosystem I
Authors: Lee J. W. , Tevault C. V. , Owens T. G. , Greenbaum E.
Published: October 2006

Contrary to the prediction of the Z-scheme model of photosynthesis, experiments demonstrated that mutants of
Chlamydomonas
containing photosystem II (PSII) but lacking photosystem I (PSI) can grow photoautotrophically with O
2
evolution, using atmospheric CO
2
as the sole carbon source. Autotrophic photosynthesis by PSI-deficient mutants was stable both under anaerobic conditions and in air (21 percent O
2
) at an actinic intensity of 200 microeinsteins per square meter per second. This PSII photosynthesis, which was sufficient to support cell development and mobility, may also occur in wild-type green algae and higher plants. The mutants can survive under 2000 microeinsteins per square meter per second with air, although they have less resistance to photoinhibition.
The Battle of the Books
Authors: Schmidt Karen
Published: October 2006

When creationists and evolutionists spar, textbooks bear the scars of battle, as publishers simply delete or skirt evolutionary topics considered too “controversial.” Educators are now watching how the advent of custom publishing—which allows local districts to order tailor-made books—and the upcoming choice of textbooks in Texas may affect the content of textbooks nationwide.
France, Germany Drop Out of ITER Race
Authors: Lawler Andrew
Published: October 2006

A surprise announcement last week that France and Germany will not be competing to host a multibillion-dollar fusion facility makes Japan the odds-on favorite as the site for the International Thermonuclear Experimental Reactor (ITER)—if it is built. Six nations were originally in the running as host for the reactor, a tokamak-shaped containment vessel that would demonstrate the feasibility of creating large amounts of electrical power. The catch is that the host country must pick up the biggest single share of the costs, which are expected to top $8 billion during a decade of construction. Japanese government and business leaders have said they are willing to put up as much of 70% of the cost, and that the time is long overdue for Asia to be the site of a major research facility.
Earth's Core Spins at Its Own Rate
Authors: Kerr Richard A.
Published: October 2006

The interior of the Earth is geologists' final frontier, a domain with much uncharted territory. Geophysicists are now pondering the implications of a recent fundamental discovery about this realm: that the solid inner core spins faster than the rest of the planet. This finding may yield new insight into the development and strength of Earth's magnetic field.
New Mammal Data Challenge Evolutionary Pulse Theory
Authors: Kerr Richard A.
Published: October 2006

Most paleontologists think climate change influences evolution, but exactly how the two are linked has been a subject of debate. One intriguing theory, the turnover pulse hypothesis proposed by paleontologist Elisabeth Vrba, suggests that abrupt climate change has driven brief pulses of evolution and extinction in animals ranging from antelopes to early human ancestors. But new data from many different animals in Africa—including many of the same species Vrba studied—show a more gradual shift in species, suggesting that climate's effect on mammalian evolution may be more complex.