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71.
Saturn's narrow F ring exhibits several unusual features that vary on timescales of hours to years. These include transient clumps, a central core surrounded by a multistranded structure and a regular series of longitudinal channels associated with Prometheus, one of the ring's two 'shepherding' satellites. Several smaller moonlets and clumps have been detected in the ring's immediate vicinity, and a population of embedded objects has been inferred. Here we report direct evidence of moonlets embedded in the ring's bright core, and show that most of the F ring's morphology results from the continual gravitational and collisional effects of small satellites, often combined with the perturbing effect of Prometheus. The F-ring region is perhaps the only location in the Solar System where large-scale collisional processes are occurring on an almost daily basis. 相似文献
72.
Molecular cloning and nucleotide sequence of a transforming gene detected by transfection of chicken B-cell lymphoma DNA 总被引:26,自引:0,他引:26
A transforming gene detected by transfection of chicken B-cell lymphoma DNA has been isolated by molecular cloning. It is homologous to a conserved family of sequences present in normal chicken and human DNAs but is not related to transforming genes of acutely transforming retroviruses. The nucleotide sequence of the cloned transforming gene suggests that it encodes a protein that is partially homologous to the amino terminus of transferrin and related proteins although only about one tenth the size of transferrin. 相似文献
73.
James J. Cooper 《西北部美国博物学家》2011,42(1)
Various aspects of the reproduction and embryology of Walker Lake Lahontan tui chub, Gila bicolor , were investigated during the spring–summer period of 1976, 1977, and 1981. Tui chub were found to spawn in littoral regions of the lake beginning in late May or early June. Early in the season male chub substantially outnumbered females over the spawning grounds, with a normal 1:1 sex ratio gradually approached as the season progressed. The developmental period between fertilization to hatch-out was shortened by increases in water temperature. Selected stages of embryonic development are described from egg fertilization through post-hatch. 相似文献
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75.
The homologue of the Duchenne locus is defective in X-linked muscular dystrophy of dogs 总被引:20,自引:0,他引:20
B J Cooper N J Winand H Stedman B A Valentine E P Hoffman L M Kunkel M O Scott K H Fischbeck J N Kornegay R J Avery 《Nature》1988,334(6178):154-156
76.
77.
N. W. Kasting W. L. Veale K. E. Cooper 《Cellular and molecular life sciences : CMLS》1981,37(9):1001-1002
Summary The AVP analog, vasotocin, administered s. c. effectively antagonized pentylenetetrazol-induced convulsions, supporting the contention that AVP may be a mediator in convulsive disorders.This work was supported by the Medical Research Council of Canada. 相似文献
78.
Structure of porphobilinogen deaminase reveals a flexible multidomain polymerase with a single catalytic site. 总被引:11,自引:0,他引:11
G V Louie P D Brownlie R Lambert J B Cooper T L Blundell S P Wood M J Warren S C Woodcock P M Jordan 《Nature》1992,359(6390):33-39
The three-domain structure of porphobilinogen deaminase, a key enzyme in the biosynthetic pathway of tetrapyrroles, has been defined by X-ray analysis at 1.9 A resolution. Two of the domains structurally resemble the transferrins and periplasmic binding proteins. The dipyrromethane cofactor is covalently linked to domain 3 but is bound by extensive salt-bridges and hydrogen-bonds within the cleft between domains 1 and 2, at a position corresponding to the binding sites for small-molecule ligands in the analogous proteins. The X-ray structure and results from site-directed mutagenesis provide evidence for a single catalytic site. Interdomain flexibility may aid elongation of the polypyrrole product in the active-site cleft of the enzyme. 相似文献
79.
80.
Summary Levels of essential and nonessential amino acids in blood of patients with an acute myocardial infarction (AMI) were found in general not to differ from values obtained from non-AMI patients. This is in contrast to blood taurine levels which are elevated in the AMI patients. 相似文献