Selective silencing of foreign DNA with low GC content by the H-NS protein in Salmonella     

Navarre WW  Porwollik S  Wang Y  McClelland M  Rosen H  Libby SJ  Fang FC 《Science (New York, N.Y.)》2006,313(5784):236-238

Horizontal gene transfer plays a major role in microbial evolution. However, newly acquired sequences can decrease fitness unless integrated into preexisting regulatory networks. We found that the histone-like nucleoid structuring protein (H-NS) selectively silences horizontally acquired genes by targeting sequences with GC content lower than the resident genome. Mutations in hns are lethal in Salmonella unless accompanied by compensatory mutations in other regulatory loci. Thus, H-NS provides a previously unrecognized mechanism of bacterial defense against foreign DNA, enabling the acquisition of DNA from exogenous sources while avoiding detrimental consequences from unregulated expression of newly acquired genes. Characteristic GC/AT ratios of bacterial genomes may facilitate discrimination between a cell's own DNA and foreign DNA.  相似文献   

Age Determination by Radiocarbon Content: World-Wide Assay of Natural Radiocarbon   总被引：2，自引：0，他引：2  

Libby WF  Anderson EC  Arnold JR 《Science (New York, N.Y.)》1949,109(2827):227-228

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Disseminated zygomycosis caused by Conidiobolus incongruus in a deer   总被引：2，自引：0，他引：2  

CP STEPHENS  JA GIBSON 《Australian veterinary journal》1997,75(5):358-359

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Chicago Radiocarbon Dates V     

Libby WF 《Science (New York, N.Y.)》1954,120(3123):733-742

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"Coulomb Staircase" at Room Temperature in a Self-Assembled Molecular Nanostructure     

RP Andres  T Bein  M Dorogi  S Feng  JI Henderson  CP Kubiak  W Mahoney  RG Osifchin  R Reifenberger 《Science (New York, N.Y.)》1996,272(5266):1323-1325

Double-ended aryl dithiols [alpha,alpha'-xylyldithiol (XYL) and 4,4'-biphenyldithiol] formed self-assembled monolayers (SAMs) on gold(111) substrates and were used to tether nanometer-sized gold clusters deposited from a cluster beam. An ultrahigh-vacuum scanning tunneling microscope was used to image these nanostructures and to measure their current-voltage characteristics as a function of the separation between the probe tip and the metal cluster. At room temperature, when the tip was positioned over a cluster bonded to the XYL SAM, the current-voltage data showed "Coulomb staircase" behavior. These data are in good agreement with semiclassical predictions for correlated single-electron tunneling and permit estimation of the electrical resistance of a single XYL molecule (approximately18 ± 12 megohms).  相似文献   

Probing the Local Effects of Magnetic Impurities on Superconductivity     

A Yazdani  BA Jones  CP Lutz  MF Crommie  DM Eigler 《Science (New York, N.Y.)》1997,275(5307):1767-1770

The local effects of isolated magnetic adatoms on the electronic properties of the surface of a superconductor were studied with a low-temperature scanning tunneling microscope. Tunneling spectra obtained near magnetic adsorbates reveal the presence of excitations within the superconductor's energy gap that can be detected over a few atomic diameters around the impurity at the surface. These excitations are locally asymmetric with respect to tunneling of electrons and holes. A model calculation based on the Bogoliubov-de Gennes equations can be used to understand the details of the local tunneling spectra.  相似文献   

Radiocarbon content of marine shells from the california and mexican west coast     

Berger R  Taylor RE  Libby WF 《Science (New York, N.Y.)》1966,153(3738):864-866

The radiocarbon content of contemporary pre-bomb marine shells from the upwelling environment of the California and the West Mexican coast has been determined. In addition, factors leading to the apparent ages of different magnitude for various marine environments are discussed.  相似文献   

A MODIFIED PHOTRONREFLECTOMETER FOR USE WITH TEST-TUBES     

Libby RL 《Science (New York, N.Y.)》1941,93(2419):459-460

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THE HISTORY OF SCIENCE     

Libby W 《Science (New York, N.Y.)》1914,40(1036):670-673

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Ice caps on venus?     

Libby WF 《Science (New York, N.Y.)》1968,159(3819):1097-1098

The data on Venus obtained by Mariner V and Venera 4 are interpreted as evidence of giant polar ice caps holding the water that must have come out of the volcanoes with the observed carbon dioxide, on the assumption that Earth and Venus are of similar composition and volcanic history. The measurements by Venera 4 of the equatorial surface temperature indicate that the microwave readings were high, so that the polar ice caps may be allowed to exist in the face of the 10-centimeter readings of polar temperature. Life seems to be distinctly possible at the edges of the ice sheets.  相似文献