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41.
42.
Alveolar function following surfactant deactivation 总被引:4,自引:0,他引:4
Nieman G. F.; Bredenberg C. E.; Clark W. R.; West N. R. 《Journal of applied physiology》1981,51(4):895-904
43.
The role of DNA sequence in determining nucleosome positions in vivo was investigated by comparing the positions adopted by nucleosomes reconstituted on a yeast plasmid in vitro using purified core histones with those in native chromatin containing the same DNA, described previously. Nucleosomes were reconstituted on a 2.5 kilobase pair DNA sequence containing the yeast TRP1ARS1 plasmid with CUP1 as an insert (TAC-DNA). Multiple, alternative, overlapping nucleosome positions were mapped on TAC-DNA. For the 58 positioned nucleosomes identified, the relative positioning strengths and the stabilities to salt and temperature were determined. These positions were, with a few exceptions, identical to those observed in native, remodeled TAC chromatin containing an activated CUP1 gene. Only some of these positions are utilized in native, unremodeled chromatin. These observations suggest that DNA sequence is likely to play a very important role in positioning nucleosomes in vivo. We suggest that events occurring in yeast CUP1 chromatin determine which positions are occupied in vivo and when they are occupied. 相似文献
44.
Molecular cloning and DNA sequence analysis of the human guanine nucleotide-binding protein Go alpha 总被引:4,自引:0,他引:4
S Lavu J Clark R Swarup K Matsushima K Paturu J Moss H F Kung 《Biochemical and biophysical research communications》1988,150(2):811-815
The nucleotide sequence of human Go alpha was determined from a partial human brain cDNA clone and the sequence of the first two 5' coding exons of a human genomic Go alpha clone. Comparison of this sequence with bovine and rat Go alpha shows greater than 90% homology at the nucleotide and deduced amino acid level. There is 100% identity at the amino acid level for the cholera and pertussis toxin-catalyzed ADP ribosylation sites, the putative guanine nucleotide binding, and the GTP hydrolysis sites. 相似文献
45.
The functional role of Asp80, a residue involved in the coordination of the Mg(2+).guanine nucleotide complex in elongation factor Tu (EF-Tu), has been investigated by its substitution with Asn in the isolated N-terminal domain (G domain). The G domain D80N is characterized by a strong decrease in binding affinity for GTP and magnesium, whereas the affinity for GDP is unchanged. This effect can be mimicked in wild-type G domain by the addition of EDTA. In contrast to this, EDTA does not essentially influence the selective effects of the mutation on the GTP and GDP binding of G domain D80N, indicating that the action of Asp80 is mainly mediated by the GTP-coordinated magnesium ion. The GTPase activity of the G domain D80N is very unstable, but can be markedly stabilized by the addition of glycerol without essentially modifying the specific effects of the mutation. In the absence of glycerol G domain D80N can express a short-lived GTPase activity. The presence of glycerol transforms this evanescent activity into a linear multiple-round activity that under optimal conditions can be almost 2 orders of magnitude higher than the GTPase of wild-type G domain. This enhanced catalytic activity represents the most striking consequence of the mutation and stresses the key role of Asp80 in the GTPase of EF-Tu.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
46.
J. Clark 《Helgoland Marine Research》1980,33(1-4):721-731
The process of coastal zone management in the United States has progressed to the point that it is now possible to embrace
whole coastal ecosystems in management programs. The structural and dynamical features of the ecosystems have to be known
before management can succeed. Furthermore, it is necessary to disaggregate the systems into subsystems. The following six
subsystems have been used as the best compromise between scientific and administrative needs: the watershed terrain, the land
drainage system, the coastal basin, the basin floor, the coastal waters, and the ocean. The Apalachicola National Estuarine
Sanctuary in Florida is used as a case history of a managed ecosystem. 相似文献
47.
Oral glucose 75 g was given to 352 patients with chronic glaucoma, acute glaucoma, or ocular hypertension and 73 patients without glaucoma. The proportion of patients with shallow anterior chambers who showed an abnormal response was significantly greater than that in patients with deep anterior chambers and in the control group (p less than 0.005). The probability of developing an abnormal response to oral glucose tests increased as the depth of the anterior chamber decreased; these two variables showed a significant negative linear correlation (r = -0.79, p less than 0.001). The high prevalence of autonomic dysfunction in patients with shallow anterior chambers and glaucoma may explain this association. Because of this, acute glaucoma should be regarded as a symptom of diabetes. 相似文献
48.
Stephen J. Clark Richard W. Thompson 《Human ecology: an interdisciplinary journal》1987,15(3):289-300
Births in Greene County, Alabama for the years 1980–1984 were examined and an overall seasonal trend was found with a peak from August through November. This trend was found to be most pronounced among women greater than 24 yeas old, and among multiparous women, and to be negatively correlated with seasonal variations in temperature and daylight. The phenomenon is likely multifactorial in origin, with sociocultural factors playing a considerable role. The influence of increasing maternal age and parity in the expression of the seasonal trend may be a function of age-related changes in families, with nuclear families acting as the most powerful potentiators of seasonality. 相似文献
49.
50.
Two simulations of plankton dynamics are combined: an N/P/Zmodel and an optimal foraging strategy dependent on variablevertical migration. We show that there is no optimal individualstrategy consistent with a copepod population that has two generationsand is a significant grazer on its limiting food supply. Alternativeroles for did vertical migration are considered. 相似文献