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排序方式: 共有275条查询结果,搜索用时 15 毫秒
91.
Mustard JF Murchie SL Pelkey SM Ehlmann BL Milliken RE Grant JA Bibring JP Poulet F Bishop J Dobrea EN Roach L Seelos F Arvidson RE Wiseman S Green R Hash C Humm D Malaret E McGovern JA Seelos K Clancy T Clark R Marais DD Izenberg N Knudson A Langevin Y Martin T McGuire P Morris R Robinson M Roush T Smith M Swayze G Taylor H Titus T Wolff M 《Nature》2008,454(7202):305-309
Phyllosilicates, a class of hydrous mineral first definitively identified on Mars by the OMEGA (Observatoire pour la Mineralogie, L'Eau, les Glaces et l'Activitié) instrument, preserve a record of the interaction of water with rocks on Mars. Global mapping showed that phyllosilicates are widespread but are apparently restricted to ancient terrains and a relatively narrow range of mineralogy (Fe/Mg and Al smectite clays). This was interpreted to indicate that phyllosilicate formation occurred during the Noachian (the earliest geological era of Mars), and that the conditions necessary for phyllosilicate formation (moderate to high pH and high water activity) were specific to surface environments during the earliest era of Mars's history. Here we report results from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) of phyllosilicate-rich regions. We expand the diversity of phyllosilicate mineralogy with the identification of kaolinite, chlorite and illite or muscovite, and a new class of hydrated silicate (hydrated silica). We observe diverse Fe/Mg-OH phyllosilicates and find that smectites such as nontronite and saponite are the most common, but chlorites are also present in some locations. Stratigraphic relationships in the Nili Fossae region show olivine-rich materials overlying phyllosilicate-bearing units, indicating the cessation of aqueous alteration before emplacement of the olivine-bearing unit. Hundreds of detections of Fe/Mg phyllosilicate in rims, ejecta and central peaks of craters in the southern highland Noachian cratered terrain indicate excavation of altered crust from depth. We also find phyllosilicate in sedimentary deposits clearly laid by water. These results point to a rich diversity of Noachian environments conducive to habitability. 相似文献
92.
The oxygen isotope ratio (delta(18)O) of cellulose is thought to provide a record of ambient temperature and relative humidity during periods of carbon assimilation. Here we introduce a method to resolve tree-canopy leaf temperature with the use of delta(18)O of cellulose in 39 tree species. We show a remarkably constant leaf temperature of 21.4 +/- 2.2 degrees C across 50 degrees of latitude, from subtropical to boreal biomes. This means that when carbon assimilation is maximal, the physiological and morphological properties of tree branches serve to raise leaf temperature above air temperature to a much greater extent in more northern latitudes. A main assumption underlying the use of delta(18)O to reconstruct climate history is that the temperature and relative humidity of an actively photosynthesizing leaf are the same as those of the surrounding air. Our data are contrary to that assumption and show that plant physiological ecology must be considered when reconstructing climate through isotope analysis. Furthermore, our results may explain why climate has only a modest effect on leaf economic traits in general. 相似文献
93.
King N Westbrook MJ Young SL Kuo A Abedin M Chapman J Fairclough S Hellsten U Isogai Y Letunic I Marr M Pincus D Putnam N Rokas A Wright KJ Zuzow R Dirks W Good M Goodstein D Lemons D Li W Lyons JB Morris A Nichols S Richter DJ Salamov A Sequencing JG Bork P Lim WA Manning G Miller WT McGinnis W Shapiro H Tjian R Grigoriev IV Rokhsar D 《Nature》2008,451(7180):783-788
Choanoflagellates are the closest known relatives of metazoans. To discover potential molecular mechanisms underlying the evolution of metazoan multicellularity, we sequenced and analysed the genome of the unicellular choanoflagellate Monosiga brevicollis. The genome contains approximately 9,200 intron-rich genes, including a number that encode cell adhesion and signalling protein domains that are otherwise restricted to metazoans. Here we show that the physical linkages among protein domains often differ between M. brevicollis and metazoans, suggesting that abundant domain shuffling followed the separation of the choanoflagellate and metazoan lineages. The completion of the M. brevicollis genome allows us to reconstruct with increasing resolution the genomic changes that accompanied the origin of metazoans. 相似文献
94.
Carlton JM Adams JH Silva JC Bidwell SL Lorenzi H Caler E Crabtree J Angiuoli SV Merino EF Amedeo P Cheng Q Coulson RM Crabb BS Del Portillo HA Essien K Feldblyum TV Fernandez-Becerra C Gilson PR Gueye AH Guo X Kang'a S Kooij TW Korsinczky M Meyer EV Nene V Paulsen I White O Ralph SA Ren Q Sargeant TJ Salzberg SL Stoeckert CJ Sullivan SA Yamamoto MM Hoffman SL Wortman JR Gardner MJ Galinski MR Barnwell JW Fraser-Liggett CM 《Nature》2008,455(7214):757-763
The human malaria parasite Plasmodium vivax is responsible for 25-40% of the approximately 515 million annual cases of malaria worldwide. Although seldom fatal, the parasite elicits severe and incapacitating clinical symptoms and often causes relapses months after a primary infection has cleared. Despite its importance as a major human pathogen, P. vivax is little studied because it cannot be propagated continuously in the laboratory except in non-human primates. We sequenced the genome of P. vivax to shed light on its distinctive biological features, and as a means to drive development of new drugs and vaccines. Here we describe the synteny and isochore structure of P. vivax chromosomes, and show that the parasite resembles other malaria parasites in gene content and metabolic potential, but possesses novel gene families and potential alternative invasion pathways not recognized previously. Completion of the P. vivax genome provides the scientific community with a valuable resource that can be used to advance investigation into this neglected species. 相似文献
95.
96.
Yagoda N von Rechenberg M Zaganjor E Bauer AJ Yang WS Fridman DJ Wolpaw AJ Smukste I Peltier JM Boniface JJ Smith R Lessnick SL Sahasrabudhe S Stockwell BR 《Nature》2007,447(7146):864-868
Therapeutics that discriminate between the genetic makeup of normal cells and tumour cells are valuable for treating and understanding cancer. Small molecules with oncogene-selective lethality may reveal novel functions of oncoproteins and enable the creation of more selective drugs. Here we describe the mechanism of action of the selective anti-tumour agent erastin, involving the RAS-RAF-MEK signalling pathway functioning in cell proliferation, differentiation and survival. Erastin exhibits greater lethality in human tumour cells harbouring mutations in the oncogenes HRAS, KRAS or BRAF. Using affinity purification and mass spectrometry, we discovered that erastin acts through mitochondrial voltage-dependent anion channels (VDACs)--a novel target for anti-cancer drugs. We show that erastin treatment of cells harbouring oncogenic RAS causes the appearance of oxidative species and subsequent death through an oxidative, non-apoptotic mechanism. RNA-interference-mediated knockdown of VDAC2 or VDAC3 caused resistance to erastin, implicating these two VDAC isoforms in the mechanism of action of erastin. Moreover, using purified mitochondria expressing a single VDAC isoform, we found that erastin alters the permeability of the outer mitochondrial membrane. Finally, using a radiolabelled analogue and a filter-binding assay, we show that erastin binds directly to VDAC2. These results demonstrate that ligands to VDAC proteins can induce non-apoptotic cell death selectively in some tumour cells harbouring activating mutations in the RAS-RAF-MEK pathway. 相似文献
97.
98.
The flux of nitrogen from land and atmosphere to estuaries and the coastal ocean has increased substantially in recent decades. The observed increase in nitrogen loading is caused by population growth, urbanization, expanding water and sewer infrastructure, fossil fuel combustion and synthetic fertilizer consumption. Most of the nitrogen is removed by denitrification in the sediments of estuaries and the continental shelf, leading to a reduction in both cultural eutrophication and nitrogen pollution of the open ocean. Nitrogen fixation, however, is thought to be a negligible process in sub-tidal heterotrophic marine systems. Here we report sediment core data from Narragansett Bay, USA, which demonstrate that heterotrophic marine sediments can switch from being a net sink to being a net source of nitrogen. Mesocosm and core incubation experiments, together with a historic data set of mean annual chlorophyll production, support the idea that a climate-induced decrease in primary production has led to a decrease in organic matter deposition to the benthos and the observed reversal of the net sediment nitrogen flux. Our results suggest that some estuaries may no longer remove nitrogen from the water column. Instead, nitrogen could be exported to the continental shelf and the open ocean and could shift the effect of anthropogenic nitrogen loading beyond the immediate coastal zone. 相似文献
99.
TJ Pugh SD Weeraratne TC Archer DA Pomeranz Krummel D Auclair J Bochicchio MO Carneiro SL Carter K Cibulskis RL Erlich H Greulich MS Lawrence NJ Lennon A McKenna J Meldrim AH Ramos MG Ross C Russ E Shefler A Sivachenko B Sogoloff P Stojanov P Tamayo JP Mesirov V Amani N Teider S Sengupta JP Francois PA Northcott MD Taylor F Yu GR Crabtree AG Kautzman SB Gabriel G Getz N Jäger DT Jones P Lichter SM Pfister TM Roberts M Meyerson SL Pomeroy YJ Cho 《Nature》2012,488(7409):106-110
100.
Zhang J Ding L Holmfeldt L Wu G Heatley SL Payne-Turner D Easton J Chen X Wang J Rusch M Lu C Chen SC Wei L Collins-Underwood JR Ma J Roberts KG Pounds SB Ulyanov A Becksfort J Gupta P Huether R Kriwacki RW Parker M McGoldrick DJ Zhao D Alford D Espy S Bobba KC Song G Pei D Cheng C Roberts S Barbato MI Campana D Coustan-Smith E Shurtleff SA Raimondi SC Kleppe M Cools J Shimano KA Hermiston ML Doulatov S Eppert K Laurenti E Notta F Dick JE Basso G Hunger SP Loh ML Devidas M Wood B Winter S 《Nature》2012,481(7380):157-163