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81.
Hong D Gupta R Ancliff P Atzberger A Brown J Soneji S Green J Colman S Piacibello W Buckle V Tsuzuki S Greaves M Enver T 《Science (New York, N.Y.)》2008,319(5861):336-339
Understanding cancer pathogenesis requires knowledge of not only the specific contributory genetic mutations but also the cellular framework in which they arise and function. Here we explore the clonal evolution of a form of childhood precursor-B cell acute lymphoblastic leukemia that is characterized by a chromosomal translocation generating a TEL-AML1 fusion gene. We identify a cell compartment in leukemic children that can propagate leukemia when transplanted in mice. By studying a monochorionic twin pair, one preleukemic and one with frank leukemia, we establish the lineal relationship between these "cancer-propagating" cells and the preleukemic cell in which the TEL-AML1 fusion first arises or has functional impact. Analysis of TEL-AML1-transduced cord blood cells suggests that TEL-AML1 functions as a first-hit mutation by endowing this preleukemic cell with altered self-renewal and survival properties. 相似文献
82.
An RNA processing activity that debranches RNA lariats 总被引:68,自引:0,他引:68
The excised introns of pre-messenger RNA's (pre-mRNA's) and intron-containing splicing intermediates are in a lariat configuration in which the 5' end of the intron is covalently joined by a 2',5'-phosphodiester bond to a specific adenosine residue near the 3' end of the intron. A 2',5'-phosphodiesterase activity in HeLa cell extracts has been detected that debranches RNA lariats, converting them to linear RNA molecules by specific cleavage of the 2',5'-phosphodiester bond. This lariat debranching activity is distinct from previously reported 2',5'-phosphodiesterases with regard to its biochemical and substrate requirements as well as its stringent cleavage specificity. The debranching activity is observed only if the RNA lariats generated during in vitro processing are deproteinized and added back to the extract. These results suggest that during the normal in vitro splicing reaction the 2',5'-phosphodiester bond of RNA lariats is protected from cleavage by the lariat debranching activity. 相似文献
83.
The use of scanning tunneling microscopy in an electrochemical environment as a tool for the nanoscale modification of gold electrodes was demonstrated. Small copper clusters, typically two to four atomic layers in height, were precisely positioned on a gold(111) electrode by a process in which copper was first deposited onto the tip of the scanning tunneling microscope, which then acted as a reservoir from which copper could be transferred to the surface during an appropriate approach of the tip to the surface. Tip approach and position were controlled externally by a microprocessor unit, allowing the fabrication of various patterns, cluster arrays, and "conducting wires" in a very flexible and convenient manner. 相似文献
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Coordinated observations of the earth's bow shock were made as Vela 3A and Explorer 33 passed within 6 earth radii of each other. Elapsed time measurements of shock motion give directly determined velocities in the range 1 to 10 kilometers per second and establish the existence of two regions, one of large amplitude magnetic "shock" oscillations and another of smaller, sunward, upstream oscillations. Each region is as thick as 1 earth radius, or more. 相似文献
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