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排序方式: 共有101条查询结果,搜索用时 62 毫秒
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Y Deng J Zhao D Sakurai KM Kaufman JC Edberg RP Kimberly DL Kamen GS Gilkeson CO Jacob RH Scofield CD Langefeld JA Kelly ME Alarcón-Riquelme BIOLUPUS GENLES Networks JB Harley TJ Vyse BI Freedman PM Gaffney KM Sivils JA James TB Niewold RM Cantor W Chen BH Hahn EE Brown PROFILE BP Tsao 《Arthritis research & therapy》2012,14(Z3):A5
45.
Background
Pichia stipitis xylose reductase (Ps-XR) has been used to design Saccharomyces cerevisiae strains that are able to ferment xylose. One example is the industrial S. cerevisiae xylose-consuming strain TMB3400, which was constructed by expression of P. stipitis xylose reductase and xylitol dehydrogenase and overexpression of endogenous xylulose kinase in the industrial S. cerevisiae strain USM21. 相似文献46.
de Oliveira Pinheiro Ricardo Boddey Lúcia H. James Euan K. Sprent Janet I. Boddey Robert M. 《Plant and Soil》2002,246(2):151-166
Recent microscopic evidence acquired using strain-specific monoclonal antibodies and specific gene probes confirms earlier claims that some strains of Azospirillum lipoferum and A. brasilense, but not others, are capable of infecting the interior of wheat roots. The present study was performed to determine whether this strain specificity in the infection of the interior of wheat roots was apparent in the first 24 h of adsorption (`anchoring') of Azospirillum cells to the root surface. Strains of A. brasilense, originally isolated from surface-sterilised wheat roots (Sp 245, Sp 107) or with a proven ability to infect the interior of wheat roots (Sp 245), showed no greater ability to anchor to the roots than other Azospirillum strains isolated from the wheat rhizosphere (Sp 246) or from the rhizosphere or rhizosphere soil of other gramineae (Sp 7, Cd, S 82). The SEM images showed that at the root tip the Azospirillum cells were principally located in cracks between epidermal cells. In the root hair zone the bacteria were more numerous but again principally located in the depressions between epidermal cells. In all zones of the roots mucilage was present, and near the tip this appeared to have been partially digested, forming `halos' around the bacteria and revealing fibril-like strands attached to the bacteria. Subsequent studies were conducted using a technique originally developed for investigating competition of rhizobia for adsorption sites on legume roots. In the adaptation of this technique it was found that the presence of any significant concentration of Ca++ in the incubation medium reduced bacterial adsorption, as did concentrations of (PO4)3- above 50 mM. The influence of the pH of the incubation medium on the adsorption of ten different strains of Azospirillum showed, that with one exception, strains isolated from the roots or rhizosphere of wheat showed optimum adsorption at pH 6.0, and all other strains pH 7.0. Apart from this effect of pH no differences in adsorption were detected between strains with a proven capacity to infect wheat roots and those unable to do so. However, strains varied in their capability to compete for adsorption sites, there being a tendency for strains with a proven capacity to invade the internal tissues of wheat roots to be more competitive for adsorption sites. 相似文献
47.
Reduced natural selection associated with low recombination in Drosophila melanogaster 总被引:8,自引:1,他引:7
Synonymous codons are not used equally in many organisms, and the extent of
codon bias varies among loci. Earlier studies have suggested that more
highly expressed loci in Drosophila melanogaster are more biased,
consistent with findings from several prokaryotes and unicellular
eukaryotes that codon bias is partly due to natural selection for
translational efficiency. We link this model of varying selection intensity
to the population-genetics prediction that the effectiveness of natural
selection is decreased under reduced recombination. In analyses of 385 D.
melanogaster loci, we find that codon bias is reduced in regions of low
recombination (i.e., near centromeres and telomeres and on the fourth
chromosome). The effect does not appear to be a linear function of
recombination rate; rather, it seems limited to regions with the very
lowest levels of recombination. The large majority of the genome apparently
experiences recombination at a sufficiently high rate for effective natural
selection against suboptimal codons. These findings support models of the
Hill-Robertson effect and genetic hitchhiking and are largely consistent
with multiple reports of low levels of DNA sequence variation in regions of
low recombination.
相似文献
48.
Kappa-chain constant-region gene sequences in genus Rattus: coding regions are diverging more rapidly than noncoding regions 总被引:2,自引:0,他引:2
We have determined the nucleotide sequence of a 1,200-base pair (bp)
genomic fragment that includes the kappa-chain constant-region gene (C
kappa) from two species of native Australian rodents, Rattus leucopus
cooktownensis and Rattus colletti. Comparison of these sequences with each
other and with other rodent C kappa genes shows three surprising features.
First, the coding regions are diverging at a rate severalfold higher than
that of the nearby noncoding regions. Second, replacement changes within
the coding region are accumulating at a rate at least as great as that of
silent changes. Third, most of the amino acid replacements are localized in
one region of the C kappa domain--namely, the carboxy-terminal "bends" in
the alpha-carbon backbone. These three features have previously been
described from comparisons of the two allelic forms of C kappa genes in R.
norvegicus. These data imply the existence of considerable evolutionary
constraints on the noncoding regions (based on as yet undetermined
functions) or powerful positive selection to diversify a portion of the
constant-region domain (whose physiological significance is not known).
These surprising features of C kappa evolution appear to be characteristic
only of closely related C kappa genes, since comparison of rodent with
human sequences shows the expected greater conservation of coding regions,
as well as a predominance of silent nucleotide substitutions within the
coding regions.
相似文献
49.
F. F. Duque M. C. P. Neves A. A. Franco R. L. Victoria R. M. Boddey 《Plant and Soil》1985,88(3):333-343
Summary A field experiment was performed to assess the effects of Rhizobium inoculation and nitrogen fertilizer (100 kg N ha–1) on four cultivars of Phaseolus beans; Carioca, Negro Argel, Venezuela 350 and Rio Tibagi. In the inoculated treatment 2.5 kg N ha–1 of15N labelled fertilizer was added in order to apply the isotope dilution technique to quantify the contribution of N2 fixation to the nutrition of these cultivars.Nodulation of all cultivars in the uninoculated treatments was poor, but the cultivars Carioca and Negro Argel were well nodulated when inoculated. Even when inoculated, nodulation of the cultivars Venezuela 350 and Rio Tibagi was poor and these cultivars showed little response to inoculation in terms of nitrogen accumulation or grain yield. The estimates of the contribution of N2 fixation estimated using the isotope dilution technique, for the Carioca and Negro Argel cultivars, amounted to 31.7 and 18.4 kg N ha–1 respectively. These two cultivars produced 991 and 883 kg ha–1 of grain, respectively, when inoculated and 663 and 620 kg ha–1 with the addition of 100 kg N ha–1 of N fertilizer. The response to nitrogen was particularly poor due to high leaching losses in the very sandy soil at the experimental site.The Venezuela 350 and Rio Tibagi cultivars only responded to N fertilizer and not to inoculation with Rhizobium which stresses the great importance of selecting plant cultivars for nitrogen fixation in the field. 相似文献
50.
R Quintero‐Torres HA Castillo‐Matadamas Jeff F Young RM Bermúdez Cruz 《Luminescence》2014,29(5):440-444
Relaxation dynamics is universal in science and engineering; its study serves to parameterize a system's response and to help identify a microscopic model of the processes involved. When measured data for a phenomenon cannot be fitted using one exponential, the choice of an alternative function to describe the decay becomes nontrivial. Here, we contrast two different, but fundamentally related approaches to fitting nontrivial decay curves; exponential decomposition and the gamma probability density function. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献