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81.
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
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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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A spectrum of comet Austin (1988 c(1)) has been obtained from 910 to 1180 A. Three bright emission lines were detected, including a forbidden oxygen line (1128 A), which are attributable to radiative pumping of neutral oxygen by solar Lyman beta. The relative strengths of the observed features should prove to be a useful diagnostic of the physical conditions and radiation fields in cometary comae. In addition, the absence of strong spectral features from highly volatile species such as He, Ar, or N(2) can be used to place constraints on the thermal environment under which the comet was formed and has been processed. 相似文献
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Green WK 《Science (New York, N.Y.)》1925,62(1616):555-557