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91.
Comparison of models for nucleotide substitution used in maximum- likelihood phylogenetic estimation 总被引:31,自引:15,他引:16
Using real sequence data, we evaluate the adequacy of assumptions made in
evolutionary models of nucleotide substitution and the effects that these
assumptions have on estimation of evolutionary trees. Two aspects of the
assumptions are evaluated. The first concerns the pattern of nucleotide
substitution, including equilibrium base frequencies and the
transition/transversion-rate ratio. The second concerns the variation of
substitution rates over sites. The maximum-likelihood estimate of tree
topology appears quite robust to both these aspects of the assumptions of
the models, but evaluation of the reliability of the estimated tree by
using simpler, less realistic models can be misleading. Branch lengths are
underestimated when simpler models of substitution are used, but the
underestimation caused by ignoring rate variation over nucleotide sites is
much more serious. The goodness of fit of a model is reduced by ignoring
spatial rate variation, but unrealistic assumptions about the pattern of
nucleotide substitution can lead to an extraordinary reduction in the
likelihood. It seems that evolutionary biologists can obtain accurate
estimates of certain evolutionary parameters even with an incorrect
phylogeny, while systematists cannot get the right tree with confidence
even when a realistic, and more complex, model of evolution is assumed.
相似文献
92.
Pot experiments were conducted with a calcareous soil (Inceptisol) to elucidate the effects of bicarbonate (0 and 20 mM) and root zone temperature (15° and 25°C) on the uptake of Zn, Fe, Mn and Cu by "Zn-efficient" and "Zn-inefficient" rice cultivars. Bicarbonate decreased concentrations and total uptake of Zn in shoots of "Zn-inefficient" cultivars, especially of IR 26 at 25°C, but not in Zn-efficient cultivars. Bicarbonate decreased concentrations and uptake of Fe in shoots of Zn inefficient cultivars, particularly in IR 26. Concentrations and total uptake of Mn were lower in bicarbonate treatment in the Zn-inefficient cultivars at 15°C, and in all cultivars at 25°C. However, concentration and uptake of Cu were not affected by bicarbonate in all cultivars. Compared to the 25°C root zone temperature, the concentrations and total uptake of both Zn and Cu in shoots at 15°C were lower in Zn-inefficient than in the Zn-efficient cultivars. The results indicate that Zn-efficiency in rice is causally related to high tolerance of plant to elavated bicarbonate concentrations in soil solution. 相似文献
93.
Divalent cation and lipid-protein interactions of biomembranes 总被引:1,自引:0,他引:1
Divalent cations play an important role in the functions of biomembranes. This review deals with three topics: (1) Mg2+-mediated change in physical state of phospholipid induces conformation and activity change of reconstituted mitochondrial H+-ATPase, (2) a proper transmembrane Ca2+ gradient is essential for the higher enzymatic activity of adenylate cyclase, and (3) role of transmembrane Ca2+ gradient in the modulation of reconstituted sarcoplasmic reticulm Ca2+-ATPase activity. 相似文献
94.
T. C. Pan T. H. Lin C. L. Tseng M. H. Yang C. W. Huang 《Biological trace element research》1993,39(2-3):117-128
Blackfoot disease is a peripheral vascular disease resulting in gangrene of the lower extremities. Though extensive epidemiological
study has implicated that high arsenic content in artesian well water of the endemic area, bears some important connection
with the disease, the etiology of the disease is still unknown. In this study, attention is paid to multielement determination
in order to find out whether the trace elements in hair of Blackfoot disease patients are different from those of the controls.
Experimental results indicate that the concentrations of As and Se in hair of patients are significantly higher than those
of the controls, but Ca and Zn are significantly lower than those of the controls. The possible connection of these elements
with the etiology of the disease is discussed. 相似文献
95.
In a previous report [Yanget al., (1987a),J. Biol Chem. 262, 7034–7040], a cyclic-AMP- and calcium-independent brain kinase which requires autophosphorylation for activity was identified as a very potent myelin basic protein (MBP) kinase. In this report, the phosphorylation sites of MBP by this autophosphorylation-dependent protein kinase (autokinase) are further determined by two-dimensional electrophoresis/thin-layer chromatography, phosphoamino acid analysis, high-performance liquid chromatography, tryptic peptide mapping, sequential manual Edman degradation, and direct peptide sequencing. Autokinase phosphorylates MBP on both threonine and serine residues. Three major tryptic phosphopeptide peaks were resolved by C18-reversed phase highper-formance liquid chromatography. Sequential manual Edman degradation together with direct sequence analysis revealed that FS(p)WGAEGQKPGFGYGGR is the phosphorylation site sequence (molar ratio ~1.0) for the first major phosphopeptide peak. When mapping with bovine brain MBP sequence, we finally demonstrate Ser115, one of thein vivo phosphorylation sites in MBP, as the major site phosphorylated by autokinase, implicating a physiologically relevant role of autokinase in the regulation of brain myelin function. By using the same approach, we also identified HRDT(p)GILDSLGR (molar ratio ~0.9) and TT(p)HYGSLPQK (molar ratio ~0.8) as the major phosphorylation site sequences in32P-MBP phosphorylated by autokinase, further indicating that -Arg-XSer/Thr-(neutral amino acid)3-(amino acid-containing hydroxyl group such as Ser/Glu/Asp)-(neutral amino acid)2-may represent a unique consensus sequence motif specifically recognized by this autophosphorylation-dependent multisubstrate/ multifunctional protein kinase in the brain. 相似文献
96.
Yang S. P.; Bergo G. W.; Krasney E.; Krasney J. A. 《Journal of applied physiology》1994,76(1):303-313
97.
98.
通过对N、P、K不同施肥条件下的“秦油2号”油菜植株内含物等与萝卜蚜有翅率关系的研究,建立了8个数学模型,结果表明可溶性糖、总N、糖与蛋白质之比和丝氨酸与萝卜蚜有翅率有密切关系,其次是天门冬氨酸、苏氨酸、谷氨酸、甘氨酸、丙氨酸、蛋氨酸、异亮氨酸、亮氨酸、酪氨酸、含水量、水溶性蛋白、酰胺氮和含P量等. 相似文献
99.
The effect of hydration on the dynamics of trimethoprim bound to dihydrofolate reductase. A deuterium NMR study. 下载免费PDF全文
To determine the effect of hydration on the dynamics of a protein complex, we used deuterium nuclear magnetic resonance (NMR) techniques to examine a trimethoprim (TMP)/E. coli dihydrofolate reductase (DHFR) complex in its lyophilized, partially hydrated, polycrystalline, and ammonium sulfate-precipitated states. The results indicate that TMP is rigid in the lyophilized powder state. The dynamic behavior could be restored by partial rehydration. At 30 wt% hydration the deuterium spectrum of the partially hydrated sample was indistinguishable from that of the polycrystalline and ammonium sulfate-precipitated samples, suggesting that the structure of the protein/TMP complex is similar in the three physical states. Furthermore, we found that the para- and meta-methoxyl groups have very different dynamical behavior. 相似文献
100.
东方蝾螈繁殖生态的研究 总被引:17,自引:2,他引:15
本文报道东方蝾螈(Cynops orientalis)的繁殖生态,内容有精巢分叶、精子形态、怀卵量、性征、性比、求偶、交配、纳精、产卵及孵化等,并对产卵场中性比的周年变化、精包形态、精子存活力及与蓝尾蝾螈的种间差异进行了观察和讨论。 相似文献