大肠杆菌pheA与tyrB基因的克隆与串联表达

为探讨用基因工程的手段改良苯丙氨酸的发酵菌株，采用聚合酶链反应（ＰＣＲ）的方法，从大肠杆菌总ＤＮＡ中克隆得到了编码苯丙氨酸合成途中的两个关键酶基因－即分枝酸变位酶（ＣＭ）／预苯酸脱水酶（ＰＤ）基因ｐｈｅＡ与苯丙氨酸转氨酶（ＰＡＴ）基因ｔｙｒＢ，在大肠杆菌中进行了这两个基因的单个和串联表达。ｐｈｅＡ和ｔｙｒＢ基因分别都能在λ噬菌体的ＰＲ启动子之后得到较大量的表达，在ＳＤＳ－ＰＡＧＥ上出现清晰的条带，     

Stable expression of the bacterial neor gene in Leishmania enriettii

Molecular genetic studies in parasitic protozoa have been hindered by the lack of methods for the introduction and expression of modified or foreign genes in these organisms. Two recent reports described the transient expression of the bacterial chloramphenicol acetyl transferase (CAT) gene under the control of parasite-specific sequences. We now describe the stable expression of a selectable marker, the gene for neomycin resistance (neor) in Leishmania enriettii. A chimaeric gene containing the neor gene inserted between two alpha-tubulin intergenic sequences was introduced into the cells and drug-resistant L. enriettii were observed which stably expressed the neor gene. One goal of this work was to analyse the sequences necessary for trans-splicing of messenger RNA, as trypanosomatids have a novel process of RNA trans-splicing, described initially in Trypanosome brucei and subsequently in several other trypanosomatids, including L. enriettii. Many trypanosomatid genes are arranged in tandem arrays and the intergenic sequences contain both the splice acceptor site for the addition of the spliced leader sequence and a putative polyadenylation site. Messenger RNA isolated from several different neor L. enrietti lines contained the spliced leader sequence joined to the neor gene at the position of the splice acceptor site in the alpha-tubulin intergenic sequence. The neor mRNA was also polyadenylated. Plasmid DNA is present within the drug-resistant organisms and appears to be extrachromosomal. The development of these methods allows the functional analysis of sequences necessary for trans-splicing.     

Role of ion flux in the control of c-fos expression

There has been much interest in the biochemical and biophysical processes that couple extracellular signals to alterations in gene expression. While many early events associated with the treatment of cells with growth factors have been described (for example, ion flux and protein phosphorylation), it has proved difficult to establish biochemical links to gene expression. Recently, the study of such genomic control signals has been facilitated by the demonstration that the c-fos proto-oncogene is rapidly and transiently induced by treatment of several cell types with polypeptide growth factors and other growth modulating substances. In one particular system it has been shown that nerve growth factor (NGF) causes a transient induction of c-fos in the phaeochromocytoma cell line PC12, within 15 min. Furthermore, the magnitude of this induction can be modulated with pharmacological agents such as peripheral-type benzodiazepines (BZDs). Thus, the study of c-fos expression in PC12 cells could yield valuable clues to the coupling mechanisms linking cell surface activation to genomic events. Here we demonstrate that c-fos is induced in PC12 cells either by receptor-ligand interaction or by agents or conditions that effect voltage-dependent calcium channels.     

一株融合菌的构建及其调剖特征研究

利用原生质体融合的方法构建了微生物采油菌株,并通过其耐温、产糖量等指标筛选了一株优秀的融合子RH18.适应性实验表明,RH18在40℃下能代谢不溶于水的生物多糖,在有杂菌的地层水中也能生长代谢;岩心驱替实验表明,RH18在多孔介质中流动会优先进入大孔道,发酵产糖后能较好地封堵大孔道、调整吸水剖面和提高非均质油层的采收率;从岩心剖面电镜照片上观察到了生物多糖的形状及其分布,分析了融合菌调剖堵水的微观机理.     

SPECT图像重建中的衰减校正算法比较

为克服单光子发射计算机断层显像中 ,会出现假阳性的结果。利用胸部数学模型和投影算法得到发射和透射的投影数据 ,采用校正算法重建发射断层图像 ,再与模型数据相比较 ,从而确定各算法的收敛性和收敛速度 ,总结出选择合适的衰减校正算法 ,并提出了将多目标优化方法应用于衰减校正的设想。     

基于基因表达调控的进化模型

为了研究生物进化过程中高级复杂结构的出现和不同复杂程度的各种结构并存的现象 ,建立了一个简单的进化模型。在模型中 ,考虑了基因的表达调控过程 ,借鉴了生命作为复杂系统的自组织现象 ,提出了基因突变产生的系列突变效果。在模仿生物的进化的实验过程中 ,出现了由简单结构向复杂结构进化的趋势。对这一过程进行了理论分析 ,将模型推广到多个物种的情况 ,并结合生物学中的现象 ,得出了结论 :生物演化过程中 ,同时存在进化与退化的趋势 ;高级复杂结构的出现是在一定的外界环境下 ,生物种群内部出现的自组织过程     

转基因表达的精细调控

将细胞特异性表达启动子与可诱导系统相结合 ,建立可用于植物转基因表达时、空、量三维调控的基因开关系统 ,为功能基因组研究及通过基因工程技术对植物代谢实施精确调控提供了全新的思路     

Heterologous expression of a bacterial haemoglobin improves the growth properties of recombinant Escherichia coli

Rational design of novel as well as improved cellular biocatalysts by genetic manipulation of cellular metabolism has recently attracted considerable interest. A wide range of bacteria have been genetically modified by integrating new enzymatic functions into their metabolic network. A central problem in the aerobic growth of any cell culture is the maintenance of dissolved oxygen (DO) concentrations above growth-limiting levels especially in high cell-density fermentations which are usually of a fed-batch type. The optimal rate of nutrient addition (and consequently the productivity) is ultimately limited by the rate at which cells can aerobically catabolize the carbon source without generating growth-inhibitory metabolites such as lactate and acetate. All approaches thus far have concentrated on improving the oxygen mass transfer rates by manipulating various environmental parameters. We have isolated the gene for a haemoglobin-like molecule, expressed by the aerobic bacterium Vitreoscilla in poorly-oxygenated environments, and expressed it in Escherichia coli. The recombinant cells contain enhanced haem as well as active haemoglobin, and they grow faster and to considerably greater cell densities than comparable plasmid-containing cells which do not express haemoglobin. This haemoglobin increases the rate of oxygen use, especially when dissolved oxygen is less than 5% of air saturation.     

声学FDTD法完全匹配层数和衰减系数对衰减性能的影响

分析了声学时域有限差分(FDTD)法中完全匹配层(PML)层数、衰减系数对吸收效果的影响.通过建立研究PML边界吸收性能的模型发现:PML边界层层数和衰减系数的选择相互关联;边界层数越多,PML的吸收效果越好,但计算量增大;层数一定时,需要为各衰减层设置合适的衰减系数,以减少衰减系数差异带来的数值反射;在实际计算中,应...     

碳纳米管薄膜氢等离子体的微波衰减特性

研究了电子碰撞和自由电子密度分布对铁催化高压歧化生成的单壁碳纳米管中氢等离子体微波衰减的影响,运用Wentzel-Kramers-Brillouin(WKB)法理论推导了碳纳米管薄膜氢等离子体的微波衰减系数公式.模拟结果表明,随着单壁碳纳米管薄膜氢等离子体中自由电子密度的线性增加,衰减吸收峰值增加,衰减吸收峰向高频方向移动.随着电子有效碰撞频率的增加,衰减吸收峰向低频方向做微小移动.铁催化高压歧化生成的碳纳米管薄膜中氢等离子体对3-4 GHz的微波产生强烈衰减吸收.     

A gene expression atlas of the central nervous system based on bacterial artificial chromosomes

The mammalian central nervous system (CNS) contains a remarkable array of neural cells, each with a complex pattern of connections that together generate perceptions and higher brain functions. Here we describe a large-scale screen to create an atlas of CNS gene expression at the cellular level, and to provide a library of verified bacterial artificial chromosome (BAC) vectors and transgenic mouse lines that offer experimental access to CNS regions, cell classes and pathways. We illustrate the use of this atlas to derive novel insights into gene function in neural cells, and into principal steps of CNS development. The atlas, library of BAC vectors and BAC transgenic mice generated in this screen provide a rich resource that allows a broad array of investigations not previously available to the neuroscience community.     

Progress in artificial control system for gene expression

Along with the increasingly wide application of transgenic techniques, new stricter criteria have been raised for controlling the expression of exogenous genes. For these demands, a series of artificial control systems for gene expression have been developed and testified in recent years, which can control exogenous genes expression in exact time and certain level by administration of a specific drug or hormone. The successful construction of these systems offers a practicable method to control precise expression of exogenous gene in organisms, and raises the feasibility of wide application of gene therapy.     

平面电磁波在等离子体中的吸收衰减

研究等离子体在隐身技术中的应用.采用垂直入射线极化平面电磁波斜入射到具有金属衬底的等离子体层的模型,利用W.K.B解,推导出电磁波能量衰减与电磁波频率和等离子体密度的关系式.在此基础上,对不同入射角的电磁波在等离子体密度为均匀分布、线性分布和指数分布情况下传播的能量衰减进行了数值计算.结果表明,电磁波衰减随等离子体密度以及电磁波入射角增加而增加;在3种分布情况下电磁波能量衰减规律是相似的.     

微波衰减测量技术的进展

论述了二端口网络衰减的各种定义及它们与散射矩阵参数的关系。从高新技术的发展和物理学实验的需要彰显出微波衰减测量的意义。计算了MASER放大器噪声温度测量误差与衰减测量误差的关系;为保证|dTe|≤1K,要求|dA|/A≤6×10-3。微波衰减测量可通过多种方法进行,例如射频代替法(微波代替法)、中频代替法等;其中以中频代替法的精确度最高,因为它用工作在30MHz频率上的截止衰减器作为标准。一级衰减标准使用圆截止波导,其中场幅按可精确计算的常数α沿波导长度方向指数地减小。例如,我国的衰减标准|dα|/α≤5×10-5。然而在通常的物理学实验中,例如测量双三棱镜的间隙的衰减时,测量可用网络分析仪法而完成;此法已广泛应用于各种实验工作。     

电信线对电磁干扰的衰减

本文论证了电信线对电磁干扰衰减,阐述了衰减与敏感系数的关系,并推导了衰减的计算公式,然后说明了CCITT现有计算公式未计入衰减.     

Natural Biological Attenuation of Benzene in Groundwater

IntroductionBenzene is a toxic contaminant often detectedin high concentration above the allowable limits ingroundwater beneath petro- chemical plants.Theprocesses for removing benzene from groundwaterinclude adsorption by activated carbon,airstripping,chemical oxidation,and biologicaldegradation[1] .Pumping the benzene out of theground and treating itexternally is commonly usedbutis expensive and requires long periods of time.The method of in situ biological degradation isthought to be cost- …