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Nuclear transport mechanisms 总被引:7,自引:0,他引:7
The term nuclear transport, refers to the movement of a large variety of macromolecules both into and out of the nucleus. Transport must be extremely selective, yet also very efficient. A single type of channel, the nuclear pore complex, mediates all movement across the nuclear envelope. Selectivity is achieved through the use of families of soluble factors that target substrates for import and export and deliver them to their appropriate intracellular destinations. We now have a fairly detailed understanding of the basic mechanisms of protein import into the nucleus. Many of these same principles can be applied to protein export and perhaps RNA export. This review will summarize the current status of what is known about various transport pathways and highlight the questions that remain to be answered. 相似文献
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Quimby RM Kulkarni SR Kasliwal MM Gal-Yam A Arcavi I Sullivan M Nugent P Thomas R Howell DA Nakar E Bildsten L Theissen C Law NM Dekany R Rahmer G Hale D Smith R Ofek EO Zolkower J Velur V Walters R Henning J Bui K McKenna D Poznanski D Cenko SB Levitan D 《Nature》2011,474(7352):487-489
Supernovae are stellar explosions driven by gravitational or thermonuclear energy that is observed as electromagnetic radiation emitted over weeks or more. In all known supernovae, this radiation comes from internal energy deposited in the outflowing ejecta by one or more of the following processes: radioactive decay of freshly synthesized elements (typically (56)Ni), the explosion shock in the envelope of a supergiant star, and interaction between the debris and slowly moving, hydrogen-rich circumstellar material. Here we report observations of a class of luminous supernovae whose properties cannot be explained by any of these processes. The class includes four new supernovae that we have discovered and two previously unexplained events (SN 2005ap and SCP 06F6) that we can now identify as members of the same class. These supernovae are all about ten times brighter than most type Ia supernova, do not show any trace of hydrogen, emit significant ultraviolet flux for extended periods of time and have late-time decay rates that are inconsistent with radioactivity. Our data require that the observed radiation be emitted by hydrogen-free material distributed over a large radius (~10(15) centimetres) and expanding at high speeds (>10(4) kilometres per second). These long-lived, ultraviolet-luminous events can be observed out to redshifts z?>?4. 相似文献
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Li W Bloom JS Podsiadlowski P Miller AA Cenko SB Jha SW Sullivan M Howell DA Nugent PE Butler NR Ofek EO Kasliwal MM Richards JW Stockton A Shih HY Bildsten L Shara MM Bibby J Filippenko AV Ganeshalingam M Silverman JM Kulkarni SR Law NM Poznanski D Quimby RM McCully C Patel B Maguire K Shen KJ 《Nature》2011,480(7377):348-350
Type Ia supernovae are thought to result from a thermonuclear explosion of an accreting white dwarf in a binary system, but little is known of the precise nature of the companion star and the physical properties of the progenitor system. There are two classes of models: double-degenerate (involving two white dwarfs in a close binary system) and single-degenerate models. In the latter, the primary white dwarf accretes material from a secondary companion until conditions are such that carbon ignites, at a mass of 1.38 times the mass of the Sun. The type Ia supernova SN 2011fe was recently detected in a nearby galaxy. Here we report an analysis of archival images of the location of SN 2011fe. The luminosity of the progenitor system (especially the companion star) is 10-100 times fainter than previous limits on other type Ia supernova progenitor systems, allowing us to rule out luminous red giants and almost all helium stars as the mass-donating companion to the exploding white dwarf. 相似文献
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P. S. Fetterman N. J. Doorenbos E. S. Keith M. W. Quimby 《Cellular and molecular life sciences : CMLS》1971,27(8):988-990
Résumé La chromatographie gazeuse des extraits de la marihuana donne la quantité complète de chaque composant cannabinoïque; tandis que la silylation des extraits précédant la chromatographie gazeuse, fournit des informations indépendentes sur les formes acides et non acides de chaque composant cannabinoïque.
Department of Pharmacognosy, School of Pharmacy, University of Mississippi, research supported by National Institute of Mental Health, Contract No. HSM-42-70-109. 相似文献
Department of Pharmacognosy, School of Pharmacy, University of Mississippi, research supported by National Institute of Mental Health, Contract No. HSM-42-70-109. 相似文献
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Nugent PE Sullivan M Cenko SB Thomas RC Kasen D Howell DA Bersier D Bloom JS Kulkarni SR Kandrashoff MT Filippenko AV Silverman JM Marcy GW Howard AW Isaacson HT Maguire K Suzuki N Tarlton JE Pan YC Bildsten L Fulton BJ Parrent JT Sand D Podsiadlowski P Bianco FB Dilday B Graham ML Lyman J James P Kasliwal MM Law NM Quimby RM Hook IM Walker ES Mazzali P Pian E Ofek EO Gal-Yam A Poznanski D 《Nature》2011,480(7377):344-347
Type Ia supernovae have been used empirically as 'standard candles' to demonstrate the acceleration of the expansion of the Universe even though fundamental details, such as the nature of their progenitor systems and how the stars explode, remain a mystery. There is consensus that a white dwarf star explodes after accreting matter in a binary system, but the secondary body could be anything from a main-sequence star to a red giant, or even another white dwarf. This uncertainty stems from the fact that no recent type Ia supernova has been discovered close enough to Earth to detect the stars before explosion. Here we report early observations of supernova SN 2011fe in the galaxy M101 at a distance from Earth of 6.4 megaparsecs. We find that the exploding star was probably a carbon-oxygen white dwarf, and from the lack of an early shock we conclude that the companion was probably a main-sequence star. Early spectroscopy shows high-velocity oxygen that slows rapidly, on a timescale of hours, and extensive mixing of newly synthesized intermediate-mass elements in the outermost layers of the supernova. A companion paper uses pre-explosion images to rule out luminous red giants and most helium stars as companions to the progenitor. 相似文献
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