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31.
32.
A stochastic model for cooperative transitions in biological systems based on a Markov chain is proposed. This model requires only two parameters, the mean probability, p, and the coupling capacity, Deltap, which measure the probability of forming a new weak bond depending on the number of similar bonds already formed and it is also responsible for the transition. In this paper we show how the model works for a large number of identical molecules and how it can be useful for studying the noise around the centre of the transition where, increasing the degree of cooperativity, i.e. the number n in the well-known Hill equation, the width of the noise increases along with its fractal dimension. A simple relationship between the degree of cooperativity and the parameter Deltap is proposed, suggesting that the cooperativity of real biological transitions is related to the coupling capacity Deltap of the present model. 相似文献
33.
苏云金芽孢杆菌δ-内毒素基因穿梭质粒的构建 总被引:1,自引:0,他引:1
在农业生产中长期使用化学农药已对环境和生态平衡造成一定破坏作用,同时有不少害虫也逐渐产生抗药性从而引起某些害虫的大流行,给农业生产带来巨大损失。应用苏云金杆菌杀虫蛋白基因(Bt基因)可构建具有抗虫作用的抗虫工程菌,这样通过拌种或植物叶面喷雾可达到快速、经济、有效的防治虫害的目的。国际上抗虫工程菌研究应用很快,如美国将BI基因转入到一种正常情况下定居在植物组织中的棒杆菌,将这种工程菌拌玉米种子,这样随植物生长该菌在植物体内大量繁殖,当玉米螟在茎和叶取食时,即因食用表达苏云金杆菌毒蛋白的工程菌而死亡。 田颖川等已克隆了苏云金芽孢杆菌内毒素基因CryIA(b)和CryIA(c)。本文将Bt基因CryIA(c)插入到大肠-枯草穿梭载体pBE-2中构建成Bt毒蛋白基因穿梭质粒pAMY,利用电穿孔法转人大肠杆菌DH5a,枯草芽孢杆菌B.subtilis BR151,IA511,野生型蜡状芽孢杆菌B.cereusa-47,短芽孢杆菌B.brevis A-5和枯草芽孢杆菌90-8,获得了具有较高杀虫活性的工程菌克隆。 相似文献
34.
贝氏隐孢子虫在珍珠鸡体内发育的扫描电镜观察 总被引:4,自引:0,他引:4
采用扫描电镜观察了贝氏隐孢子虫在珍珠鸡体内的发育。大量球形虫体镶嵌于气管和法氏囊微绒毛丛中。气管纤毛消失,微绒毛生发生融合。法氏囊粘膜表面可观察到宿主细胞突起,在突起的表面有数个虫体寄生。滋养体呈球状,平均大小为1.7μm。裂殖体拥有4个或8个香蕉状裂殖子。成熟大配子体大小为 4.2 × 3.3μm,在其侧面可观察到锯齿状突起。偶尔能观察到卵囊,其表 面有一明显裂缝。虫体逸出后所留下的带虫空泡似弹坑状,根据其结构可将其分为两类,其中一类为裂殖子或小配子的形成场所,另一类为卵囊的形成场所。 相似文献
35.
重组人GM—CSF基因在昆虫细胞中的表达 总被引:1,自引:0,他引:1
利用苜蓿夜蛾核型多角体病毒(AcNPV)带β-Galactosidase基因标记的非融合蛋白基因转移载体pBlueBac将人粒细胞巨噬细胞集落刺激因子(hGM-CSF)基因成功地插入病毒AcNPV的基因组中.hGM-CSF基因在感染重组病毒的草地夜蛾(Spodopterafrugiperda)培养细胞Sf9中得到表达,感染后的Sf9细胞培养液能刺激人骨髓细胞在体外形成典型的集落,表达水平可达2.7×1055CFU/ml。以hGM-CSF单抗所作的WesternBlotting表明,表达的hGM-CSF对是3种糖基化程度不同的产物,分子量分别约为15kd,18kd和20kd。 相似文献
36.
中国剑螽属四新种记述:直翅目:螽斯总科:蛩螽科 总被引:1,自引:0,他引:1
作者在整理陕西师范大学动物研究所标本时,发现剑螽属4新种,即膨基剑螽Xiphidiopsisinflata,sp.nov.双叶剑螽X.bifoliata,sp.nov.凸顶剑螽X.convexis,sp.nov.及叉尾剑螽X.divida,sp.nov.模式标本均存于陕西师范大学动物研究所。 相似文献
37.
This paper describes an approach to seek for mouse c-Myc/Myn proteins-bound specific sequences among genomic DNA.cDNA fragment of myn gene was obtained through RT-PCR technique from RNA of NIH3T3 cells.DNA fragments encoding BR/HLH/LZ structure of Myc and Myn proteins were cloned in frame into pGEX-2T vector respectively.Fusion GST-Myc and GST-Myn synthesized in E.coli hosts showed affinity to CACGTG E-box DNA and subsequently interacted with genomic fragments prepared through whole-genome-PCR.A PCR-assisted procedure which combines protein-DNA interaction and affinity chromatography was designed to enrich Myc/Myn bound DNA.At least two genomic DNA fragments obtained exhibit specifical binding capacity to Myc/Myn complex but not to GST alone.Significance of the work and of the technique itself as well asidentification of the DNAs are discussed. 相似文献
38.
Atomic composition of the hydrophobic and hydrophilic membrane sides of self-assembled SC3p hydrophobin. 下载免费PDF全文
H A Wsten O M de Vries H C van der Mei H J Busscher J G Wessels 《Journal of bacteriology》1994,176(22):7085-7086
The hydrophobin SC3p of Schizophyllum commune self-assembles into a 10-nm-thick amphipathic membrane at hydrophilic-hydrophobic interfaces. X-ray photoelectron spectroscopy of the hydrophobic membrane side of SC3p, assembled in vitro, showed an atomic composition similar to the calculated composition of SC3p when glycosylation was taken into account. The atomic composition measured at the hydrophilic membrane side deviated from that at the hydrophobic side and indicated the presence of a lower number of peptide bonds. High levels of S and N were detected only on mycelia carrying hydrophobic aerial hyphae, as expected with assembled SC3p present at the surface of these hyphae. 相似文献
39.
Abscisic Acid-Induced Membrane Potential Changes in Barley Aleurone Protoplasts: a Possible Relevance for the Regulation of rab Gene Expression 总被引:2,自引:0,他引:2
Heimovaara-Dijkstra Sjoukje; van Duijn Bert; Libbenga Kees R.; Heidekamp Freek; Wang Mei 《Plant & cell physiology》1994,35(5):743-750
The effect of ABA on the membrane potential of barley (Hordeumvulgare cv. Himalaya) aleurone protoplasts was studied by measuringthe distribution of the lipophilic cation tetraphenylphosphonium(TPP+). The resting membrane potential (Em) according to ourmeasurements with TPP+ is about 53 mV and is in agreementwith membrane potential values as measured with intracellularmicroelectrodes (about 55 mV). The TPP+-measurementscould demonstrate a clear dependence of the resting Em on theexternal pH (pHe). Stimulation of the protoplasts with ABA induced a transienthyperpolarization of the membrane to 62 mV as measuredwith TPP+. The hyperpolarization was ABA-concentration dependent. Inhibition of the H+-ATPases with the specific proton pump inhibitorsdiethylstilbestrol (DES) or Micanozole effectively preventedhyperpolarization. This indicates that the hyperpolarizationis consistent with the activation of plasma membrane H+-ATPases.The K+-inward rectifier inhibitor BaCl2 was able to prolongthe hyperpolarization. This result suggests that the hyperpolarizationcauses the opening of K+-channels. The ABA-induced proton-pump activation may be involved in ABA-inducedgene-expression, as DES was able to inhibit this gene expression.BaCl2 did only show a slight inhibitory effect on ABA-inducedgene-expression. (Received January 4, 1994; Accepted April 12, 1994) 相似文献
40.
Inorganic cofactors (Mn, Ca2+ and Cl-) are essential for oxidation of H2O to O2 by Photosystem II. The Mn reductants NH2OH and its N-methyl derivatives have been employed as probes to further examine the interactions between these species and Mn at the active site of H2O oxidation. Results of these studies show that the size of a hydroxylamine derivative regulates its ability to inactivate O2 evolution activity, and that this size-dependent inhibition behavior arises from the protein structure of Photosystem II. A set of anions (Cl-, F- and SO4
2-) is able to slow NH2OH and CH3NHOH inactivation of intact Photosystem II membranes by exerting a stabilizing influence on the extrinsic 23 and 17 kDa polypeptides. In contrast to this non-specific anion effect, only Cl- is capable of attenuating CH3NHOH and (CH3)2NOH inhibition in salt-washed preparations lacking the 23 and 17 kDa polypeptides. However, Cl- fails to protect against NH2OH inhibition in salt-washed membranes. These results indicate that the attack by NH2OH and its N-methyl derivatives on Mn occurs at different sites in the O2-evolving complex. The small reductant NH2OH acts at a Cl--insensitive site whereas the inhibitions by CH3NHOH and (CH3)2NOH involve a site that is Cl- sensitive. These findings are consistent with earlier studies showing that the size of primary amines controls the Cl- sensitivity of their binding to Mn in the O2-evolving complex.Abbreviation MES
4-morpholinoethanesulfonic acid
- PS II
Photosystem II 相似文献