Molecular phylogenetics of mastodon and Tyrannosaurus rex     

Organ CL  Schweitzer MH  Zheng W  Freimark LM  Cantley LC  Asara JM 《Science (New York, N.Y.)》2008,320(5875):499

We report a molecular phylogeny for a nonavian dinosaur, extending our knowledge of trait evolution within nonavian dinosaurs into the macromolecular level of biological organization. Fragments of collagen alpha1(I) and alpha2(I) proteins extracted from fossil bones of Tyrannosaurus rex and Mammut americanum (mastodon) were analyzed with a variety of phylogenetic methods. Despite missing sequence data, the mastodon groups with elephant and the T. rex groups with birds, consistent with predictions based on genetic and morphological data for mastodon and on morphological data for T. rex. Our findings suggest that molecular data from long-extinct organisms may have the potential for resolving relationships at critical areas in the vertebrate evolutionary tree that have, so far, been phylogenetically intractable.  相似文献   

Monitoring biosynthesis of wheat cell-wall phenylpropanoids in situ     

Lewis NG  Yamamoto E  Wooten JB  Just G  Ohashi H  Towers GH 《Science (New York, N.Y.)》1987,237(4820):1344-1346

Lignins and suberins are complex plant cell-wall macromolecules that are composed mainly of phenylpropanoid residues derived from L-phenylalanine. Lignins and suberins are considered to be covalently linked to carbohydrates and to lipids, respectively. The bonding of these important structural materials within cell walls has never been established. By feeding specifically labeled [(13)C] ferulic acid over extended durations to seedlings of Triticum aestivum L. and by using solid-state carbon-13 nuclear magnetic resonance techniques, the major resonances due to specific carbons in the propanoid side chains of these cell-wall polymers have been identified in situ. The signals were found to differ significantly from those of synthetic lignins, which have usually been considered to be good approximations of natural lignin structure.  相似文献   

Two-dimensional nanosheets produced by liquid exfoliation of layered materials   总被引：1，自引：0，他引：1  

Coleman JN  Lotya M  O'Neill A  Bergin SD  King PJ  Khan U  Young K  Gaucher A  De S  Smith RJ  Shvets IV  Arora SK  Stanton G  Kim HY  Lee K  Kim GT  Duesberg GS  Hallam T  Boland JJ  Wang JJ  Donegan JF  Grunlan JC  Moriarty G  Shmeliov A  Nicholls RJ  Perkins JM  Grieveson EM  Theuwissen K  McComb DW  Nellist PD  Nicolosi V 《Science (New York, N.Y.)》2011,331(6017):568-571

If they could be easily exfoliated, layered materials would become a diverse source of two-dimensional crystals whose properties would be useful in applications ranging from electronics to energy storage. We show that layered compounds such as MoS(2), WS(2), MoSe(2), MoTe(2), TaSe(2), NbSe(2), NiTe(2), BN, and Bi(2)Te(3) can be efficiently dispersed in common solvents and can be deposited as individual flakes or formed into films. Electron microscopy strongly suggests that the material is exfoliated into individual layers. By blending this material with suspensions of other nanomaterials or polymer solutions, we can prepare hybrid dispersions or composites, which can be cast into films. We show that WS(2) and MoS(2) effectively reinforce polymers, whereas WS(2)/carbon nanotube hybrid films have high conductivity, leading to promising thermoelectric properties.  相似文献   

THE SYMMETRY OF TIME IN PHYSICS     

Lewis GN 《Science (New York, N.Y.)》1930,71(1849):569-577

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Conserved sequence and structural elements in the HIV-1 principal neutralizing determinant   总被引：103，自引：0，他引：103  

G J LaRosa  J P Davide  K Weinhold  J A Waterbury  A T Profy  J A Lewis  A J Langlois  G R Dreesman  R N Boswell  P Shadduck 《Science (New York, N.Y.)》1990,249(4971):932-935

The principal neutralizing determinant (PND) of human immunodeficiency virus HIV-1 is part of a disulfide bridged loop in the third variable region of the external envelope protein, gp120. Analysis of the amino acid sequences of this domain from 245 different HIV-1 isolates revealed that the PND is less variable than thought originally. Conservation to better than 80 percent of the amino acids in 9 out of 14 positions in the central portion of the PND and the occurrence of particular oligopeptide sequences in a majority of the isolates suggest that there are constraints on PND variability. One constraining influence may be the structural motif (beta strand--type II beta turn--beta strand--alpha helix) predicted for the consensus PND sequence by a neural network approach. Isolates with a PND similar to the commonly investigated human T cell lymphoma virus IIIB (HTLV-IIIB) and LAV-1 (BRU) strains were rare, and only 14 percent of sera from 86 randomly selected HIV-1 seropositive donors contained antibodies that recognized the PND of these virus isolates. In contrast, over 65 percent of these sera reacted with peptides containing more common PND sequences. These results suggest that HIV vaccine immunogens chosen because of their similarity to the consensus PND sequence and structure are likely to induce antibodies that neutralize a majority of HIV-1 isolates.  相似文献   

Lymphocytic-choriomeningitis virus in hamster tumor: spread to hamsters and humans   总被引：6，自引：0，他引：6  

A M Lewis  W P Rowe  H C Turner  R J Huebner 《Science (New York, N.Y.)》1965,150(694):363-364

A passage line of a spontaneous hamster fibrosarcoma is contaminated by the virus. of lymphocytic choriomeningitis. Tumors from animals receiving implants when newborn contain high titers of infectious lymphocytic-choriomeningitis virus and complement-fixing antigen, and hamsters receiving implants when weanlings develop high titers of complement-fixing antibody against lymphocytic-choriomeningitis virus. In contrast with the specific reactions of tumorous hamsters to the initiating virus in virus-induced tumors, the development of complement-fixing antibody to lymphocytic-choriomeningitis virus does not depend on the development of tumors. Infant hamsters bearing the tumor have a generalized subclinical infection and seem able to spread virus to other hamsters and to humans.  相似文献   

Space perception in early infancy: perception within a common auditory-visual space?     

H McGurk  M Lewis 《Science (New York, N.Y.)》1974,186(4164):649-650

Human infants aged I to 7 months were exposed to modifications of the normal spatial relationship between their mothers' face and voice. There was no evidence that such modifications were experienced by the infants as violations of a preexisting expectancy for face and voice to occupy the same spatial location.  相似文献   

Stishovite at the cretaceous-tertiary boundary, raton, new Mexico     

McHone JF  Nieman RA  Lewis CF  Yates AM 《Science (New York, N.Y.)》1989,243(4895):1182-1184

Stishovite, a dense phase of silica, has become widely accepted as an indicator of terrestrial impact events. Stishovite occurs at several impact structures but has not been found at volcanic sites. Solid-state silicon-29 magic-angle spinning nuclear magnetic resonance (silicon-29 MAS NMR) and X-ray diffraction of samples from the Cretaceous-Tertiary boundary layer at Raton, New Mexico, indicate that stishovite occurs in crystalline mineral grains. Stishovite was indicated by a single, sharp resonance with a chemical shift value of -191.3 ppm, characteristic of silicon in octahedral coordination, that disappeared after heating the sample at 850 degrees Celsius for 30 minutes. An X-ray diffraction pattern of HF residuals from the unheated sample displayed more than 120 peaks, most of which correspond to quartz, zircon, rutile, and anatase. Eight unambiguous weak to moderate reflections could be ascribed to d-spacings characteristic of stishovite.  相似文献   

AN APPARATUS FOR PRODUCING CONSTANT GAS MIXTURES     

Lewis RA  Koepf GF 《Science (New York, N.Y.)》1941,93(2417):407-408

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THE CONTINUOUS SPECTRA OF GASES     

Lewis EP 《Science (New York, N.Y.)》1915,41(1069):947-948

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