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排序方式: 共有249条查询结果,搜索用时 31 毫秒
1.
We have isolated the delta-globin gene of the New-World spider monkey,
Ateles geoffroyi, and compared its nucleotide sequence with those of other
primate delta- and beta-globin genes. Among primate delta-globin genes, the
rate of nonsynonymous substitutions is much less than the rate of
synonymous substitutions. This suggests that primate delta- globin genes
may remain under evolutionary conservation, perhaps because hemoglobin A2
has an as yet unknown physiological importance.
相似文献
2.
Wei-Cai Yang Hayo C.J. Canter Cramers Peter Hogendijk Panagiotis Katinakis Carel A. Wijffelman Henk Franssen Albert Van Kammen Ton Bisseling 《The Plant journal : for cell and molecular biology》1992,2(2):143-151
In this paper studies on the role of flavonoids in pea root nodule development are reported. Flavonoid synthesis was followed by localizing chalcone synthase (CHS) mRNA in infected pea roots and in root nodules. In a nodule primordium, CHS mRNA is present in all cells of the primordium. Therefore it is hypothesized that the Rhizobium Nod factor induces cell division in the root cortex by stimulating the production of flavonoids that function as auxin transport inhibitors. In nodules CHS mRNA is predominantly present in a region at the apex of the nodule consisting of meristematic and cortical cells. These cells are not infected by Rhizobium. Therefore it is postulated that CHS plays a role in nodule development rather than in a defence response. In roots CHS mRNA is located at a similar position as in nodules, suggesting that CHS has the same function in both root and nodule development. When nodules are formed by mutants of Rhizobium leguminosarum bv. viciae that are unable to secrete β(1-2) glucan and to synthesize the O-antigen containing LPS I, CHS genes are also expressed in regions of the nodule that are infected by Rhizobium. It is postulated that the impaired development of nodules formed by these mutants is due to an induction of a plant defence response. 相似文献
3.
Biochemical pathways in prokaryotes can be traced backward through evolutionary time 总被引:10,自引:0,他引:10
For the first time, a credible prokaryotic phylogenetic tree is being
assembled by Woese and others using quantitative sequence analysis of
oligonucleotides in the highly conservative rRNA. This provides an
evolutionary scale against which the evolutionary steps that led to the
arrangement and regulation of contemporary biochemical pathways can be
measured. This paper presents an emerging evolutionary picture of aromatic
amino acid biosynthesis within a large superfamily assemblage of
prokaryotes that is sufficiently developed to illustrate a new perspective
that will be applicable to many other biochemical pathways.
相似文献
4.
Jacques Hille Frank Verheggen Peter Roelvink Henk Franssen Ab van Kammen Pim Zabel 《Plant molecular biology》1986,7(3):171-176
Summary Plant cells are sensitive to the antibiotic bleomycin, a DNA damaging glycopeptide. A bleomycin resistance determinant, located on transposon Tn5 and functional in bacteria, has been cloned in a plant expression vector and introduced into Nicotiana plumbaginifolia using Agrobacterium tumefaciens. The expression of this determinant in plant cells confers resistance to bleomycin and allows selection of transformed plant cells. 相似文献
5.
An activator of blood coagulation factor X was found in the venom of the horned viper Cerastes cerastes, and was purified by gel filtration, ion-exchange chromatography and chromatofocussing. The activator is a protein composed of a heavy and a light polypeptide chain linked by disulfide bonds. Two subforms of the activator were found. Both contained a heavy chain of Mr 58000 and are distinguished from each other by the presence of two different light chains of Mr 17700 and 15000. The activator appears to cleave the bond in the factor X molecule that is also cleaved by factor IXa. Factor X activation by the activator is strongly stimulated by Ca2+. The kinetic parameters for the activation reaction have been determined. A Km for factor X of 19.2 nM and a Vmax of 0.11 pmol of Xa/min per ng venom were found. 相似文献
6.
In Drosophila pseudoobscura, the amylase (Amy) multigene family is
contained within a series of inversions, or gene arrangements, on the third
chromosome. The Standard (ST), Santa Cruz (SC), and Tree Line (TL)
inversions are central to the phylogeny of arrangements, and have clusters
of other arrangements derived from them. The gene arrangements belonging to
each of these three clusters have a characteristic number of Amy genes,
ranging from three in ST to two in SC to one in TL. This distribution
pattern can reflect a history of either duplications or deletions, although
the data available in the past did not permit a decision between these
alternatives. We provide unambiguous evidence that three Amy genes were
present before the divergence of the ST, SC, and TL arrangements. Thus, the
current status of the Amy multigene family is the result of deletions in
the TL and SC arrangements, which created three new pseudogenes: TL
Amy2-psi, TL Amy3-psi, and SC Amy3- psi. Analysis of pseudogene sequences
revealed that, in the SC and ST arrangements, pseudogene evolution has been
retarded, most likely due to the homogenization effect of gene conversion.
Finally, by determining the original copy number, we have reconstructed the
evolutionary history of the Amy multigene family and linked it with the
evolution of the central gene arrangements.
相似文献
7.
The application of sensory methodology for measuring deodorizing effect of an air conditioner equipped with electric plasma was introduced. Deodorizing effect was measured using chemical and sensory methods at different time (0, 30 and 60 min) and mode (control, blowing and cooling) of an air conditioner. Smoke from a roll of cigarette in a closed room was used as a source of odor and the concentrations of acetic acid and ammonia were measured as odorous chemical components. As one of the sensory methods triangle test was used and as a first step to obtain deodorizing effects by triangle test, the threshold of each panelist was obtained as the log dilution ratio of odor concentration at which the difference from odorless air was detected. The odor concentration at each time and mode was calculated using the threshold of the panel and the deodorizing effect was obtained on the basis of the odor concentration. In addition to a triangle test, scaling methods such as category scaling or magnitude estimation were used to measure deodorizing effect of an air conditioner. Deodorizing effects by scaling methods were calculated based on odor intensity with time at each mode. The regression analysis was done between the efficacy of deodorizing effect by sensory test and those by acetic acid and ammonia, the R2 values of the regression equations for triangle test, category scale, and magnitude estimation were 0.84, 0.72 and 0.69, respectively. Deodorizing effect by triangle test explained the decrease of acetic acid and ammonia better than those by category scaling or magnitude estimation while high cost and time consuming labor involved in triangle tests reduced the merit. The results of this study demonstrated that various sensory methods could be used to measure deodorizing effect of air conditioners and further researches on fast and reliable methods are needed to establish the official procedures. 相似文献
8.
C. A. G. M. Weijers H. Jongejan M. C. R. Franssen A. de Groot J. A. M. de Bont 《Applied microbiology and biotechnology》1995,42(5):775-781
A broad range of epoxyalkanes was converted into the corresponding ketones by cell extracts of Xanthobacter Py2. Both 1,2- and 2,3-epoxyalkanes were degraded and in addition, the degradation of 2,3-epoxyalkanes in all cases was highly enantioselective. Conversion of a deuterium-labelled substrate indicated that the ketone product was probably formed indirectly via an hydroxy intermediate. Degradation of epoxyalkanes by Xanthobacter Py2 was dependent on both NAD and another, not yet identified, cofactor that was present in the low-molecular-mass fraction (LMF) of propene-grown cells. It is proposed that the LMF was involved in a reductive reaction step since it could be replaced by dithiothreitol (DTT) and various other dithiol compounds. Epoxyalkane-degrading activity was inhibited by the sulphhydryl blocking reagent N-ethylmaleimide (NEM). Inhibition by NEM and stimulation by LMF, DTT and other dithiols was effective only in the simultaneous presence of NAD. 相似文献
9.
10.
For phototropic curvature of a green sunflower seedling, only the hypocotyl has to be illuminated; the tip and cotyledons are not involved in stimulus perception. The etiolated seedling is phototropically insensitive, illumination of only the hypocotyl renders it sensitive. It is concluded that the photoreceptor is located within the responding organ. In curving seedlings, the endogenous indoleacetic acid (IAA) remains evenly distributed. However, the inhibitor, xanthoxin (Xa), accumulates on the illuminated side. The degree of phototropic response is generally related to the concentration of Xa. The amount of phototropic curvature is independent of the rate of elongation growth, the former can be changed without affecting the latter, and vice versa. The data conflict with the Cholodny-Went theory, whereas they support the hypothesis of Blaauw that the phototropic reaction is caused by the local accumulation of a growth-inhibiting substance on the irradiated side.Abbreviations CCC
chlormequat, (2-chloroethyl)trimethylammonium chloride
- GA3
gibberellic acid
- IAA
indole-3-acetic acid
- Xa
xanthoxin 相似文献