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排序方式: 共有436条查询结果,搜索用时 15 毫秒
391.
Biological activity of a polar metabolite of vitamin D 总被引:8,自引:0,他引:8
392.
Two distinct steps in nuclear envelope assembly can be assayed in vitro: the protein-mediated binding of nuclear-specific vesicles to chromatin, and the subsequent fusion of these vesicles to enclose the chromatin within a double nuclear membrane. Nuclear vesicle fusion, like fusion in the secretory pathway, requires ATP and cytosol and is inhibited by nonhydrolysable GTP analogues. The sensitivity of nuclear vesicle fusion to GTP-gamma S requires a GTP-dependent soluble factor, the properties of which are strikingly similar to a GTP-dependent Golgi binding factor (GGBF) that inhibits Golgi vesicle fusion in the presence of GTP-gamma S and belongs to the ADP-ribosylation factor (ARF) family of small GTPases. In the presence of GTP-gamma S, ARF proteins and alpha-, beta-, gamma-, delta-COP ('coatomer') subunits are associated with Golgi transport vesicles, but the exact roles of ARF proteins in secretion are not yet understood. We report here that purified ARF1 and GGBF have GTP-dependent soluble factor activity in the nuclear vesicle fusion assay. Our results show that the function of ARF is not limited to the Golgi apparatus, and indicate that there may be a link between the formation of nuclear vesicles during mitosis and proteins involved in secretion. 相似文献
393.
Mitochondrial DNA and human evolution 总被引:90,自引:0,他引:90
Mitochondrial DNAs from 147 people, drawn from five geographic populations have been analysed by restriction mapping. All these mitochondrial DNAs stem from one woman who is postulated to have lived about 200,000 years ago, probably in Africa. All the populations examined except the African population have multiple origins, implying that each area was colonised repeatedly. 相似文献
394.
395.
Analgesia: morphine-pathway block in top1 poppies 总被引:1,自引:0,他引:1
Millgate AG Pogson BJ Wilson IW Kutchan TM Zenk MH Gerlach WL Fist AJ Larkin PJ 《Nature》2004,431(7007):413-414
The opium poppy is a source of the pharmaceuticals codeine, morphine and their derived analgesics. Here we describe the initial characterization of the poppy mutant known as top1 (for 'thebaine oripavine poppy 1'), which accumulates the morphine and codeine precursors thebaine and oripavine and does not complete their biosynthesis into morphine and codeine. The original discovery of top1 stimulated a re-engineering of the opioid industry in the island state of Tasmania, which grows over 40% of the world's licit opiates, in order to produce thebaine and oripavine efficiently from morphine-free poppy crops to provide precursors for highly effective analgesics and for treatment of opioid addiction. 相似文献
396.
397.
Maximum running speed is constrained by the speed at which the limbs can be swung forwards and backwards, and by the force they can withstand while in contact with the ground. Humans sprinting around banked bends change the duration of foot contact to spread the time over which the load is applied, thereby keeping the force on their legs constant. We show here that, on entering a tight bend, greyhounds do not change their foot-contact timings, and so have to withstand a 65% increase in limb forces. This supports the idea that greyhounds power locomotion by torque about the hips, so--just as in cycling humans--the muscles that provide the power are mechanically divorced from the structures that support weight. 相似文献
398.
Adaptive evolution in the stomach lysozymes of foregut fermenters 总被引:19,自引:0,他引:19
The convergent evolution of a fermentative foregut in two groups of mammals offers an opportunity to study adaptive evolution at the protein level. The appearance of this mode of digestion has been accompanied by the recruitment of lysozyme as a bacteriolytic enzyme in the stomach both in the ruminants (for example the cow) and later in the colobine monkeys (for example the langur). The stomach lysozymes of these two groups share some physicochemical and catalytic properties that appear to adapt them for functioning in the stomach fluid. To examine the basis for these shared properties, we sequenced langur stomach lysozyme and compared it to other lysozymes of known sequence. Tree analysis suggest that, after foregut fermentation arose in monkeys, the langur lysozyme gained sequence similarity to cow stomach lysozyme and evolved two times faster than the other primate lysozymes. This rapid evolution, coupled with functional and sequence convergence upon cow stomach lysozyme, could imply that positive darwinian selection has driven about 50% of the evolution of langur stomach lysozyme. 相似文献
399.
The male-specific region of the human Y chromosome is a mosaic of discrete sequence classes 总被引:2,自引:0,他引:2
Skaletsky H Kuroda-Kawaguchi T Minx PJ Cordum HS Hillier L Brown LG Repping S Pyntikova T Ali J Bieri T Chinwalla A Delehaunty A Delehaunty K Du H Fewell G Fulton L Fulton R Graves T Hou SF Latrielle P Leonard S Mardis E Maupin R McPherson J Miner T Nash W Nguyen C Ozersky P Pepin K Rock S Rohlfing T Scott K Schultz B Strong C Tin-Wollam A Yang SP Waterston RH Wilson RK Rozen S Page DC 《Nature》2003,423(6942):825-837
400.
Extra-embryonic function of Rb is essential for embryonic development and viability 总被引:31,自引:0,他引:31
Wu L de Bruin A Saavedra HI Starovic M Trimboli A Yang Y Opavska J Wilson P Thompson JC Ostrowski MC Rosol TJ Woollett LA Weinstein M Cross JC Robinson ML Leone G 《Nature》2003,421(6926):942-947
The retinoblastoma (Rb) gene was the first tumour suppressor identified. Inactivation of Rb in mice results in unscheduled cell proliferation, apoptosis and widespread developmental defects, leading to embryonic death by day 14.5 (refs 2-4). However, the actual cause of the embryonic lethality has not been fully investigated. Here we show that loss of Rb leads to excessive proliferation of trophoblast cells and a severe disruption of the normal labyrinth architecture in the placenta. This is accompanied by a decrease in vascularization and a reduction in placental transport function. We used two complementary techniques-tetraploid aggregation and conditional knockout strategies-to demonstrate that Rb-deficient embryos supplied with a wild-type placenta can be carried to term, but die soon after birth. Most of the neurological and erythroid abnormalities thought to be responsible for the embryonic lethality of Rb-null animals were virtually absent in rescued Rb-null pups. These findings identify and define a key function of Rb in extra-embryonic cell lineages that is required for embryonic development and viability, and provide a mechanism for the cell autonomous versus non-cell autonomous roles of Rb in development. 相似文献