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91.
In metazoans, most pre-messenger RNAs contain introns that are removed by splicing. The spliced mRNAs are then exported to the cytoplasm. Recent studies showed that splicing promotes efficient mRNA export, but the mechanism for coupling these two processes is not known. Here we show that Aly, the metazoan homologue of the yeast mRNA export factor Yralp (ref. 2), is recruited to messenger ribonucleoprotein (mRNP) complexes generated by splicing. In contrast, Aly does not associate with mRNPs assembled on identical mRNAs that already have no introns or with heterogenous nuclear RNP (hnRNP) complexes. Aly is recruited during spliceosome assembly, and then becomes tightly associated with the spliced mRNP. Aly shuttles between the nucleus and cytoplasm, and excess recombinant Aly increases both the rate and efficiency of mRNA export in vivo. Consistent with its splicing-dependent recruitment, Aly co-localizes with splicing factors in the nucleus. We conclude that splicing is required for efficient mRNA export as a result of coupling between the splicing and the mRNA export machineries. 相似文献
92.
The smallest known non-avian theropod dinosaur 总被引:39,自引:0,他引:39
Non-avian dinosaurs are mostly medium to large-sized animals, and to date all known mature specimens are larger than the most primitive bird, Archaeopteryx. Here we report on a new dromaeosaurid dinosaur, Microraptor zhaoianus gen. et sp. nov., from the Early Cretaceous Jiufotang Formation of Liaoning, China. This is the first mature non-avian dinosaur to be found that is smaller than Archaeopteryx, and it eliminates the size disparity between the earliest birds and their closest non-avian theropod relatives. The more bird-like teeth, the Rahonavis-like ischium and the small number of caudal vertebrae of Microraptor are unique among dromaeosaurids and improve our understanding of the morphological transition to birds. The nearly completely articulated foot shows features, such as distally positioned digit I, slender and recurved pedal claws, and elongated penultimate phalanges, that are comparable to those of arboreal birds. The discovery of these in non-avian theropods provides new insights for studying the palaeoecology of some bird-like theropod dinosaurs. 相似文献
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Tracking an object through feature space 总被引:7,自引:0,他引:7
Visual attention allows an observer to select certain visual information for specialized processing. Selection is readily apparent in 'tracking' tasks where even with the eyes fixed, observers can track a target as it moves among identical distractor items. In such a case, a target is distinguished by its spatial trajectory. Here we show that one can keep track of a stationary item solely on the basis of its changing appearance--specified by its trajectory along colour, orientation, and spatial frequency dimensions--even when a distractor shares the same spatial location. This ability to track through feature space bears directly on competing theories of attention, that is, on whether attention can select locations in space, features such as colour or shape, or particular visual objects composed of constellations of visual features. Our results affirm, consistent with a growing body of psychophysical and neurophysiological evidence, that attention can indeed select specific visual objects. Furthermore, feature-space tracking extends the definition of visual object to include not only items with well defined spatio-temporal trajectories, but also those with well defined featuro-temporal trajectories. 相似文献
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96.
1 Results The oxidation of alcohols into the corresponding carbonyl compound is one of the most important functional group transformation in organic synthesis[1]. Traditionally,such transformations have been performed with stoichiometric inorganic oxidant or other high valent metal oxidant[2]. Despite a variety of systems for the catalytic oxidation of alcohols have been developed,there is ongoing interest in the search for new efficient and environmental friendly oxidation system.To the best of our kno... 相似文献
97.
98.
Excavations at the early Neolithic site of Jiahu in Henan Province, China have produced what may be the earliest complete, playable, tightly-dated multinote musical instruments. Jiahu was occupied from 7000 BC to 5700 BC, considerably antedating the well known Peiligang culture. Here we describe six exquisitely made complete flutes which were found in radiocarbon-dated excavation layers, along with fragments of perhaps 30 more. The flutes are made from the ulnae of the red-crowned crane (Grus japonensis Millen) and have 5, 6, 7 and 8 holes. The best preserved flute has been played and tonally analysed. In addition to early musical artefacts, the archaeological record at Jiahu contains important information on the very foundations of Chinese society. We describe the archaeological characteristics of the Jiahu site, details concerning its dating, its place in the prehistory of the Chinese Neolithic, the ethnicity of its population and the results of a tonal analysis of a nearly 9,000-year-old musical instrument found there. 相似文献
99.
利用过氧化物过氧化二异丙苯(DCP)和多官能团化合物三烯丙基异氰尿酸酯(TAIC),对聚甲基乙撑碳酸酯(PPC)进行了交联研究。研究发现, DCP和TAIC的用量对PPC的交联均有较大影响, PPC交联后,其凝胶含量、机械性能、弹性模量、玻璃化转变温度均有所增加, 1%的DCP和4%的TAIC用量可得到较理想的交联PPC材料。 相似文献
100.
Segal E Fondufe-Mittendorf Y Chen L Thåström A Field Y Moore IK Wang JP Widom J 《Nature》2006,442(7104):772-778