Sediment-dispersed extraterrestrial chromite traces a major asteroid disruption event     

Schmitz B  Häggström T  Tassinari M 《Science (New York, N.Y.)》2003,300(5621):961-964

Abundant extraterrestrial chromite grains from decomposed meteorites occur in middle Ordovician (480 million years ago) marine limestone over an area of approximately 250,000 square kilometers in southern Sweden. The chromite anomaly gives support for an increase of two orders of magnitude in the influx of meteorites to Earth during the mid-Ordovician, as previously indicated by fossil meteorites. Extraterrestrial chromite grains in mid-Ordovician limestone can be used to constrain in detail the temporal variations in flux of extraterrestrial matter after one of the largest asteroid disruption events in the asteroid belt in late solar-system history.  相似文献   

Bacterial rhodopsin: evidence for a new type of phototrophy in the sea     

Béjà O  Aravind L  Koonin EV  Suzuki MT  Hadd A  Nguyen LP  Jovanovich SB  Gates CM  Feldman RA  Spudich JL  Spudich EN  DeLong EF 《Science (New York, N.Y.)》2000,289(5486):1902-1906

Extremely halophilic archaea contain retinal-binding integral membrane proteins called bacteriorhodopsins that function as light-driven proton pumps. So far, bacteriorhodopsins capable of generating a chemiosmotic membrane potential in response to light have been demonstrated only in halophilic archaea. We describe here a type of rhodopsin derived from bacteria that was discovered through genomic analyses of naturally occuring marine bacterioplankton. The bacterial rhodopsin was encoded in the genome of an uncultivated gamma-proteobacterium and shared highest amino acid sequence similarity with archaeal rhodopsins. The protein was functionally expressed in Escherichia coli and bound retinal to form an active, light-driven proton pump. The new rhodopsin exhibited a photochemical reaction cycle with intermediates and kinetics characteristic of archaeal proton-pumping rhodopsins. Our results demonstrate that archaeal-like rhodopsins are broadly distributed among different taxa, including members of the domain Bacteria. Our data also indicate that a previously unsuspected mode of bacterially mediated light-driven energy generation may commonly occur in oceanic surface waters worldwide.  相似文献   

Acetylcholine-synthesizing T cells relay neural signals in a vagus nerve circuit     

Rosas-Ballina M  Olofsson PS  Ochani M  Valdés-Ferrer SI  Levine YA  Reardon C  Tusche MW  Pavlov VA  Andersson U  Chavan S  Mak TW  Tracey KJ 《Science (New York, N.Y.)》2011,334(6052):98-101

Neural circuits regulate cytokine production to prevent potentially damaging inflammation. A prototypical vagus nerve circuit, the inflammatory reflex, inhibits tumor necrosis factor-α production in spleen by a mechanism requiring acetylcholine signaling through the α7 nicotinic acetylcholine receptor expressed on cytokine-producing macrophages. Nerve fibers in spleen lack the enzymatic machinery necessary for acetylcholine production; therefore, how does this neural circuit terminate in cholinergic signaling? We identified an acetylcholine-producing, memory phenotype T cell population in mice that is integral to the inflammatory reflex. These acetylcholine-producing T cells are required for inhibition of cytokine production by vagus nerve stimulation. Thus, action potentials originating in the vagus nerve regulate T cells, which in turn produce the neurotransmitter, acetylcholine, required to control innate immune responses.  相似文献   

Stable carbon cycle-climate relationship during the Late Pleistocene   总被引：2，自引：0，他引：2  

Siegenthaler U  Stocker TF  Monnin E  Lüthi D  Schwander J  Stauffer B  Raynaud D  Barnola JM  Fischer H  Masson-Delmotte V  Jouzel J 《Science (New York, N.Y.)》2005,310(5752):1313-1317

A record of atmospheric carbon dioxide (CO2) concentrations measured on the EPICA (European Project for Ice Coring in Antarctica) Dome Concordia ice core extends the Vostok CO2 record back to 650,000 years before the present (yr B.P.). Before 430,000 yr B.P., partial pressure of atmospheric CO2 lies within the range of 260 and 180 parts per million by volume. This range is almost 30% smaller than that of the last four glacial cycles; however, the apparent sensitivity between deuterium and CO2 remains stable throughout the six glacial cycles, suggesting that the relationship between CO2 and Antarctic climate remained rather constant over this interval.  相似文献   

Detection of GTP-tubulin conformation in vivo reveals a role for GTP remnants in microtubule rescues     

Dimitrov A  Quesnoit M  Moutel S  Cantaloube I  Poüs C  Perez F 《Science (New York, N.Y.)》2008,322(5906):1353-1356

Microtubules display dynamic instability, with alternating phases of growth and shrinkage separated by catastrophe and rescue events. The guanosine triphosphate (GTP) cap at the growing end of microtubules, whose presence is essential to prevent microtubule catastrophes in vitro, has been difficult to observe in vivo. We selected a recombinant antibody that specifically recognizes GTP-bound tubulin in microtubules and found that GTP-tubulin was indeed present at the plus end of growing microtubules. Unexpectedly, GTP-tubulin remnants were also present in older parts of microtubules, which suggests that GTP hydrolysis is sometimes incomplete during polymerization. Observations in living cells suggested that these GTP remnants may be responsible for the rescue events in which microtubules recover from catastrophe.  相似文献   

A physical map of the 1-gigabase bread wheat chromosome 3B   总被引：2，自引：0，他引：2  

Paux E  Sourdille P  Salse J  Saintenac C  Choulet F  Leroy P  Korol A  Michalak M  Kianian S  Spielmeyer W  Lagudah E  Somers D  Kilian A  Alaux M  Vautrin S  Bergès H  Eversole K  Appels R  Safar J  Simkova H  Dolezel J  Bernard M  Feuillet C 《Science (New York, N.Y.)》2008,322(5898):101-104

As the staple food for 35% of the world's population, wheat is one of the most important crop species. To date, sequence-based tools to accelerate wheat improvement are lacking. As part of the international effort to sequence the 17-billion-base-pair hexaploid bread wheat genome (2n = 6x = 42 chromosomes), we constructed a bacterial artificial chromosome (BAC)-based integrated physical map of the largest chromosome, 3B, that alone is 995 megabases. A chromosome-specific BAC library was used to assemble 82% of the chromosome into 1036 contigs that were anchored with 1443 molecular markers, providing a major resource for genetic and genomic studies. This physical map establishes a template for the remaining wheat chromosomes and demonstrates the feasibility of constructing physical maps in large, complex, polyploid genomes with a chromosome-based approach.  相似文献   

On the origin of interictal activity in human temporal lobe epilepsy in vitro     

Cohen I  Navarro V  Clemenceau S  Baulac M  Miles R 《Science (New York, N.Y.)》2002,298(5597):1418-1421

The origin and mechanisms of human interictal epileptic discharges remain unclear. Here, we describe a spontaneous, rhythmic activity initiated in the subiculum of slices from patients with temporal lobe epilepsy. Synchronous events were similar to interictal discharges of patient electroencephalograms. They were suppressed by antagonists of either glutamatergic or gamma-aminobutyric acid (GABA)-ergic signaling. The network of neurons discharging during population events comprises both subicular interneurons and a subgroup of pyramidal cells. In these pyramidal cells, GABAergic synaptic events reversed at depolarized potentials. Depolarizing GABAergic responses in neurons downstream to the sclerotic CA1 region contribute to human interictal activity.  相似文献   

Stochastic pulse regulation in bacterial stress response     

Locke JC  Young JW  Fontes M  Hernández Jiménez MJ  Elowitz MB 《Science (New York, N.Y.)》2011,334(6054):366-369

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Arabidopsis EDS1 connects pathogen effector recognition to cell compartment-specific immune responses     

Heidrich K  Wirthmueller L  Tasset C  Pouzet C  Deslandes L  Parker JE 《Science (New York, N.Y.)》2011,334(6061):1401-1404

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Conical intersection dynamics in NO2 probed by homodyne high-harmonic spectroscopy     

Wörner HJ  Bertrand JB  Fabre B  Higuet J  Ruf H  Dubrouil A  Patchkovskii S  Spanner M  Mairesse Y  Blanchet V  Mével E  Constant E  Corkum PB  Villeneuve DM 《Science (New York, N.Y.)》2011,334(6053):208-212

Conical intersections play a crucial role in the chemistry of most polyatomic molecules, ranging from the simplest bimolecular reactions to the photostability of DNA. The real-time study of the associated electronic dynamics poses a major challenge to the latest techniques of ultrafast measurement. We show that high-harmonic spectroscopy reveals oscillations in the electronic character that occur in nitrogen dioxide when a photoexcited wave packet crosses a conical intersection. At longer delays, we observe the onset of statistical dissociation dynamics. The present results demonstrate that high-harmonic spectroscopy could become a powerful tool to highlight electronic dynamics occurring along nonadiabatic chemical reaction pathways.  相似文献