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Summary CosmopolitanDrosophila species can survive wide ecological tolerances measured by resistance to desiccation/temperature extremes compared with endemic rain forest species. This, rather than any genetic features, is important in helping to explain the widespread distributions of cosmopolitan species.We thank Dr Lee Ehrman for cultures ofD. paulistorum, and the Australian Research Grants Committee for financial support. 相似文献
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Cooperative tandem binding of met repressor of Escherichia coli 总被引:10,自引:0,他引:10
S E Phillips I Manfield I Parsons B E Davidson J B Rafferty W S Somers D Margarita G N Cohen I Saint-Girons P G Stockley 《Nature》1989,341(6244):711-715
We present biochemical and genetic data to support the hypothesis that the Escherichia coli met repressor, MetJ, binds to synthetic and natural operator sequences in tandem arrays such that repression depends not only on the affinity of the DNA-protein interaction, but also on protein-protein contacts along the tandem array. This represents a novel form of regulatory switch. Furthermore, there seems to be homology between the organization of the met and trp operators. 相似文献
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Gehrels N Norris JP Barthelmy SD Granot J Kaneko Y Kouveliotou C Markwardt CB Mészáros P Nakar E Nousek JA O'Brien PT Page M Palmer DM Parsons AM Roming PW Sakamoto T Sarazin CL Schady P Stamatikos M Woosley SE 《Nature》2006,444(7122):1044-1046
Gamma-ray bursts (GRBs) are known to come in two duration classes, separated at approximately 2 s. Long-duration bursts originate from star-forming regions in galaxies, have accompanying supernovae when these are near enough to observe and are probably caused by massive-star collapsars. Recent observations show that short-duration bursts originate in regions within their host galaxies that have lower star-formation rates, consistent with binary neutron star or neutron star-black hole mergers. Moreover, although their hosts are predominantly nearby galaxies, no supernovae have been so far associated with short-duration GRBs. Here we report that the bright, nearby GRB 060614 does not fit into either class. Its approximately 102-s duration groups it with long-duration GRBs, while its temporal lag and peak luminosity fall entirely within the short-duration GRB subclass. Moreover, very deep optical observations exclude an accompanying supernova, similar to short-duration GRBs. This combination of a long-duration event without an accompanying supernova poses a challenge to both the collapsar and the merging-neutron-star interpretations and opens the door to a new GRB classification scheme that straddles both long- and short-duration bursts. 相似文献
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I C Parsons 《Nature》1965,206(985):717-718
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G. E. Spence A. A. Hoffmann P. A. Parsons 《Cellular and molecular life sciences : CMLS》1984,40(7):763-765
Summary We have found that males of the sibling speciesD. melanogaster andD. simulans are preferentially attracted to sites marked by the residual odors of conspecific females, especially if non-virgin. In natural populations, this could enhance sexual selection among males, and cause some isolation at the microhabitat level. 相似文献