Sulfur diagenesis in everglades peat and origin of pyrite in coal     

Altschuler ZS  Schnepfe MM  Silber CC  Simon FO 《Science (New York, N.Y.)》1983,221(4607):221-227

The pattern of sulfur transformation in peat across the Everglades basin indicates that pyrite formation in organic-rich swamps depends on the use of organic oxysulfur compounds in dissimilatory respiration by sulfur-reducing bacteria. This paragenesis explains the primary distribution of sulfur compounds in low-sulfur coals and possibly in most coals and many organic-rich soils and sediments. It also accounts for the occurrence of framboidal pyrite bound in fossil tissue in coal and sediments.  相似文献   

Hematopoietic cell regulation by Rac1 and Rac2 guanosine triphosphatases     

Gu Y  Filippi MD  Cancelas JA  Siefring JE  Williams EP  Jasti AC  Harris CE  Lee AW  Prabhakar R  Atkinson SJ  Kwiatkowski DJ  Williams DA 《Science (New York, N.Y.)》2003,302(5644):445-449

The Rho guanosine triphosphatases (GTPases) Rac1 and Rac2 are critical signaling regulators in mammalian cells. The deletion of both Rac1 and Rac2 murine alleles leads to a massive egress of hematopoietic stem/progenitor cells (HSC/Ps) into the blood from the marrow, whereas Rac1-/- but not Rac2-/- HSC/Ps fail to engraft in the bone marrow of irradiated recipient mice. In contrast, Rac2, but not Rac1, regulates superoxide production and directed migration in neutrophils, and in each cell type, the two GTPases play distinct roles in actin organization, cell survival, and proliferation. Thus, Rac1 and Rac2 regulate unique aspects of hematopoietic development and function.  相似文献   

PKA type IIalpha holoenzyme reveals a combinatorial strategy for isoform diversity     

Wu J  Brown SH  von Daake S  Taylor SS 《Science (New York, N.Y.)》2007,318(5848):274-279

The catalytic (C) subunit of cyclic adenosine monophosphate (cAMP)-dependent protein kinase (PKA) is inhibited by two classes of regulatory subunits, RI and RII. The RII subunits are substrates as well as inhibitors and do not require adenosine triphosphate (ATP) to form holoenzyme, which distinguishes them from RI subunits. To understand the molecular basis for isoform diversity, we solved the crystal structure of an RIIalpha holoenzyme and compared it to the RIalpha holoenzyme. Unphosphorylated RIIalpha(90-400), a deletion mutant, undergoes major conformational changes as both of the cAMP-binding domains wrap around the C subunit's large lobe. The hallmark of this conformational reorganization is the helix switch in domain A. The C subunit is in an open conformation, and its carboxyl-terminal tail is disordered. This structure demonstrates the conserved and isoform-specific features of RI and RII and the importance of ATP, and also provides a new paradigm for designing isoform-specific activators or antagonists for PKA.  相似文献   

Poliovirus crystals within the endoplasmic reticulum of endothelial and mononuclear cells in the monkey spinal cord   总被引：9，自引：0，他引：9  

K Blinzinger  J Simon  D Magrath  L Boulger 《Science (New York, N.Y.)》1969,163(873):1336-1337

The lumbar motor columns of a cynomolgus monkey that had become tetraplegic after experimental infection with a highly virulent strain of type 3 poliovirus were examined by electron microscopy. Crystalline aggregates of poliovirus occurred within the endoplasmic reticulum of endothelial cells as well as of mononuclear inflammatory cells. This finding suggests that the endoplasmic reticulum might be much more involved in poliovirus multiplication than has been previously supposed.  相似文献   

Localized control of ligand binding in hemoglobin: effect of tertiary structure on picosecond geminate recombination   总被引：2，自引：0，他引：2  

J M Friedman  T W Scott  G J Fisanick  S R Simon  E W Findsen  M R Ondrias  V W Macdonald 《Science (New York, N.Y.)》1985,229(4709):187-190

The picosecond geminate rebinding of molecular oxygen was monitored in a variety of different human, reptilian, and fish hemoglobins. The fast (100 to 200 picoseconds) component of the rebinding is highly sensitive to protein structure. Both proximal and distal perturbations of the heme affect this rebinding process. The rebinding yield for the fast process correlates with the frequency of the stretching motion of the iron-proximal histidine mode (VFe-His) observed in the transient Raman spectra of photodissociated ligated hemoglobins. The high-affinity R-state species exhibit the highest values for VFe-His and the highest yields for fast rebinding, whereas low affinity R-state species and T-state species exhibit lower values of VFe-His and correspondingly reduced yields for this geminate process. These findings link protein control of ligand binding with events at the heme.  相似文献   

Computer science   总被引：10，自引：0，他引：10  

A Newell  A J Perlis  H A Simon 《Science (New York, N.Y.)》1967,157(795):1373-1374

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Astronomy and solar physics: measurement of the solar spectral irradiance from 200 to 3000 nanometers     

Thuillier G  Goutail JP  Simon PC  Pastiels R  Labs D  Neckel H 《Science (New York, N.Y.)》1984,225(4658):182-184

The solar spectrum experiment on Spacelab 1 measured 98 percent of the sun's total energy output. It improved the absolute accuracy of solar irradiance data, especially in the ultraviolet and infrared regions. In order to detect any variation in the spectrum on future shuttle flights, the data were obtained in a radiation scale that can be preserved with high precision over many years. The instrument performance and preliminary data reduction are described.  相似文献   

A quasi-biennial oscillation signal in general circulation model simulations     

Cariolle D  Amodei M  Déqué M  Mahfouf JF  Simon P  Teyssédre H 《Science (New York, N.Y.)》1993,261(5126):1313-1316

The quasi-biennial oscillation (QBO) is a free atmospheric mode that affects the equatorial lower stratosphere. With a quasi-regular frequency, the mean equatorial zonal wind alternates from easterly to westerly regimes. This oscillation is zonally symmetric about the equator, has its largest amplitude in the latitudinal band from 20 degrees S to 20 degrees N, and has a mean period of about 27 months. The QBO appears to originate in the momentum deposition produced by the damping in the stratosphere of equatorial waves excited by diabatic thermal processes in the troposphere. The results of three 10-year simulations obtained with three general circulation models are reported, all of which show the development in the stratosphere of a QBO signal with a period and a spatial propagating structure that are in good agreement with observations without any ad hoc parameterization of equatorial wave forcing. Although the amplitude of the oscillation in the simulations is still less than the observed value, the result is promising for the development of global climate models.  相似文献   

N-linked glycosylation in Campylobacter jejuni and its functional transfer into E. coli     

Wacker M  Linton D  Hitchen PG  Nita-Lazar M  Haslam SM  North SJ  Panico M  Morris HR  Dell A  Wren BW  Aebi M 《Science (New York, N.Y.)》2002,298(5599):1790-1793

N-linked protein glycosylation is the most abundant posttranslation modification of secretory proteins in eukaryotes. A wide range of functions are attributed to glycan structures covalently linked to asparagine residues within the asparagine-X-serine/threonine consensus sequence (Asn-Xaa-Ser/Thr). We found an N-linked glycosylation system in the bacterium Campylobacter jejuni and demonstrate that a functional N-linked glycosylation pathway could be transferred into Escherichia coli. Although the bacterial N-glycan differs structurally from its eukaryotic counterparts, the cloning of a universal N-linked glycosylation cassette in E. coli opens up the possibility of engineering permutations of recombinant glycan structures for research and industrial applications.  相似文献   

Mutations in dynein link motor neuron degeneration to defects in retrograde transport     

Hafezparast M  Klocke R  Ruhrberg C  Marquardt A  Ahmad-Annuar A  Bowen S  Lalli G  Witherden AS  Hummerich H  Nicholson S  Morgan PJ  Oozageer R  Priestley JV  Averill S  King VR  Ball S  Peters J  Toda T  Yamamoto A  Hiraoka Y  Augustin M  Korthaus D  Wattler S  Wabnitz P  Dickneite C  Lampel S  Boehme F  Peraus G  Popp A  Rudelius M  Schlegel J  Fuchs H  Hrabe de Angelis M  Schiavo G  Shima DT  Russ AP  Stumm G  Martin JE  Fisher EM 《Science (New York, N.Y.)》2003,300(5620):808-812

Degenerative disorders of motor neurons include a range of progressive fatal diseases such as amyotrophic lateral sclerosis (ALS), spinal-bulbar muscular atrophy (SBMA), and spinal muscular atrophy (SMA). Although the causative genetic alterations are known for some cases, the molecular basis of many SMA and SBMA-like syndromes and most ALS cases is unknown. Here we show that missense point mutations in the cytoplasmic dynein heavy chain result in progressive motor neuron degeneration in heterozygous mice, and in homozygotes this is accompanied by the formation of Lewy-like inclusion bodies, thus resembling key features of human pathology. These mutations exclusively perturb neuron-specific functions of dynein.  相似文献