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1.
Transformation and conjugation permit the passage of DNA through the bacterial membranes and represent dominant modes for the transfer of genetic information between bacterial cells or between bacterial and eukaryotic cells. As such, they are responsible for the spread of fitness-enhancing traits, including antibiotic resistance. Both processes usually involve the recognition of double-stranded DNA, followed by the transfer of single strands. Elaborate molecular machines are responsible for negotiating the passage of macromolecular DNA through the layers of the cell surface. All or nearly all the machine components involved in transformation and conjugation have been identified, and here we present models for their roles in DNA transport. 相似文献
2.
Beijersbergen A Dulk-Ras AD Schilperoort RA Hooykaas PJ 《Science (New York, N.Y.)》1992,256(5061):1324-1327
Agrobacterium tumefaciens transfers part of its Ti plasmid, the transferred DNA (T-DNA), to plant cells during tumor induction. Expression of this T-DNA in plant cells results in their transformation into tumor cells. There are similarities between the process of T-DNA transfer to plants and the process of bacterial conjugation. Here, the T-DNA transfer machinery mediated conjugation between bacteria. Thus, products of the Vir region of the Ti plasmid of Agrobacterium tumefaciens, normally involved in transfer of DNA from bacteria to plants, can direct the conjugative transfer of an IncQ plasmid between agrobacteria. 相似文献
3.
以生菜（Lactuca sativa）“申选5号”与“罗莎红”为材料,采用PCR-DGGE 和Real-Time PCR 技术,分析了土壤栽培系统和基质栽培系统根际细菌群落的差异。Real-Time PCR 检测结果表明,基质栽培的两个生菜品种根际细菌数量均显著高于土壤（P<0.05）;PCR-DGGE图谱条带结果表明,根际细菌群落多样性基质高于土壤。栽培系统是造成多样性差异的主要原因,但也与品种有关：“申选5 号”基质的Shannon-Wiener 指数（H）,Simpson 指数（D）和均匀度（E）均显著高于土壤（P<0.05）;“罗莎红”基质的H 显著高于土壤,而D和E 无显著差异。结合土壤和基质理化性质的RDA 分析结果,土壤和基质具有不同的细菌群落,pH 值与硝态氮是塑造根际细菌群落的主要因子,含水量、碳氮比和有效磷与细菌群落的形成呈正相关。 相似文献
4.
Structure of ribonuclease H phased at 2 A resolution by MAD analysis of the selenomethionyl protein 总被引：32，自引：0，他引：32
Ribonuclease H digests the RNA strand of duplex RNA.DNA hybrids into oligonucleotides. This activity is indispensable for retroviral infection and is involved in bacterial replication. The ribonuclease H from Escherichia coli is homologous with the retroviral proteins. The crystal structure of the E. coli enzyme reveals a distinctive alpha-beta tertiary fold. Analysis of the molecular model implicates a carboxyl triad in the catalytic mechanism and suggests a likely mode for the binding of RNA.DNA substrates. The structure was determined by the method of multiwavelength anomalous diffraction (MAD) with the use of synchrotron data from a crystal of the recombinant selenomethionyl protein. 相似文献
5.
蜂王浆介导外源基因转移的初步研究 总被引：1，自引：0，他引：1
采用DNA延滞实验研究蜂王浆与DNA的结合能力,然后通过蜂群哺育和人工培育两种方式,对1日龄工蜂幼虫进行短期饲喂,初步研究蜂王浆介导绿色荧光蛋白基因的方法和转移情况.结果表明:在蜂群环境下,蜂王浆中的外源DNA短期内不会完全被分解;但用蜂王浆作媒介并未实现蜜蜂基因转染,蜜蜂能否通过蜂王浆介导实现基因转移,还需进一步探讨. 相似文献
6.
将生物素标记的DNA与链霉亲和素(streptavidin,STV)按4∶1摩尔比连接,用原子力显微镜(atomic force microscope,AFM)对混合物表征,观察到所有可能的几种DNA-STV复合物。并按照不同摩尔浓度比和孵育时间配制DNA与STV混合液,探讨了影响结合效率的因素,初步得到用生物素-链霉亲和素系统批量制备1STV-1DNA单分子复合物的最佳制备条件,为未来单分子DNA的大规模快速制备奠定了基础。 相似文献
7.
Regulation of the Amount of Starch in Plant Tissues by ADP Glucose Pyrophosphorylase 总被引：2，自引：0，他引：2
Starch, a major storage metabolite in plants, positively affects the agricultural yield of a number of crops. Its biosynthetic reactions use adenosine diphosphate glucose (ADPGlc) as a substrate; ADPGlc pyrophosphorylase, the enzyme involved in ADPGlc formation, is regulated by allosteric effectors. Evidence that this plastidial enzyme catalyzes a rate-limiting reaction in starch biosynthesis was derived by expression in plants of a gene that encodes a regulatory variant of this enzyme. Allosteric regulation was demonstrated to be the major physiological mechanism that controls starch biosynthesis. Thus, plant and bacterial systems for starch and glycogen biosynthesis are similar and distinct from yeast and mammalian systems, wherein glycogen synthase has been demonstrated to be the rate-limiting regulatory step. 相似文献
8.
[目的]构建未引入任何遗传标记物的溶藻弧菌vscC基因框内缺失突变株。[方法]首先以溶藻弧菌ZJ51-O基因组DNA为模板,用重叠延伸PCR(gene splicing by overlapext ension PCR,SOE-PCR)扩增法构建体外vscC基因缺失片段;扩增产物经酶切后连接至自杀质粒pDM4,再转化入大肠杆菌SY327进行克隆,筛选阳性克隆子并进行PCR分析鉴定;提取阳性克隆子的自杀重组质粒pDM4-△vscC,用热休克法将其转入到大肠杆菌S17-1中,再经接合生殖的方式将自杀重组质粒导入溶藻弧菌ZJ51-O菌株中,利用抗生素筛选策略与蔗糖反向筛选系统,挑选疑似目的突变菌株,最后利用PCR鉴定与测序分析进行确证。[结果]溶藻弧菌ZJ51-O的vscC基因框内缺失突变株构建成功。[结论]该研究为进一步研究vscC基因的功能和T3SS在溶藻弧菌致病过程中所起的作用奠定基础,同时也为溶藻弧菌的其他基因突变株的构建和研究提供了参考和试验经验。 相似文献
9.
DNA glycosylases must interrogate millions of base pairs of undamaged DNA in order to locate and then excise one damaged nucleobase. The nature of this search process remains poorly understood. Here we report the use of disulfide cross-linking (DXL) technology to obtain structures of a bacterial DNA glycosylase, MutM, interrogating undamaged DNA. These structures, solved to 2.0 angstrom resolution, reveal the nature of the search process: The protein inserts a probe residue into the helical stack and severely buckles the target base pair, which remains intrahelical. MutM therefore actively interrogates the intact DNA helix while searching for damage. 相似文献
10.
Navarre WW Porwollik S Wang Y McClelland M Rosen H Libby SJ Fang FC 《Science (New York, N.Y.)》2006,313(5784):236-238
Horizontal gene transfer plays a major role in microbial evolution. However, newly acquired sequences can decrease fitness unless integrated into preexisting regulatory networks. We found that the histone-like nucleoid structuring protein (H-NS) selectively silences horizontally acquired genes by targeting sequences with GC content lower than the resident genome. Mutations in hns are lethal in Salmonella unless accompanied by compensatory mutations in other regulatory loci. Thus, H-NS provides a previously unrecognized mechanism of bacterial defense against foreign DNA, enabling the acquisition of DNA from exogenous sources while avoiding detrimental consequences from unregulated expression of newly acquired genes. Characteristic GC/AT ratios of bacterial genomes may facilitate discrimination between a cell's own DNA and foreign DNA. 相似文献
11.
The mechanism of DNA transfer in the mating system of an archaebacterium 总被引：15，自引：0，他引：15
The genetic transfer system in the extremely halophilic archaebacterium Halobacterium volcanii is the only archaebacterial mating system known. The mechanism of genetic transfer of this archaebacterium was studied by using the immobile plasmids pHV2 and pHV11 as cytoplasmic markers. It was found that the cytoplasms of the parental types do not mix during the mating process, that each parental type can serve both as a donor and as a recipient, and that cytoplasmic bridges, with dimensions of up to 2 micrometers long and 0.1 micrometer in diameter, were formed between the parental types. These bridges appear to be used for the transfer of DNA from one cell to another. If so, this archaebacterial mating system is different from both eubacterial conjugation and eukaryotic sexual cell fusion. 相似文献
12.
有毒有机物影响DNA酶解和抗生素抗性基因横向迁移 总被引：1，自引：1，他引：0
进入环境中的有毒有机物种类较多、分布广泛。大量生命遗传物质DNA与有毒有机物共存于污染环境中,由于抗生素滥用,一些DNA上携带着抗生素抗性基因(ARGs);有毒有机物和ARGs复合污染严重危害着生态安全和人群健康。有毒有机物如何影响DNA酶解和ARGs迁移,这已成为环境领域研究的热点之一,近些年来,该领域研究取得一些重要进展。有毒有机物可通过共价作用、非共价作用、剪切作用与DNA结合,进而改变DNA分子结构、影响DNA酶解;有毒有机物也可通过改变DNA降解酶活性或占据DNA上降解酶的酶切位点,进而影响DNA酶解过程。环境中ARGs横向迁移主要有接合、转导、转化三种方式,有毒有机物影响ARGs横向迁移的机制主要包括:有毒有机物调控可动遗传因子、引起细胞SOS反应、胁迫细胞形成自然感受态、影响生物膜形成、改变细胞膜通透性、与胞外质粒形成加合物。进入细胞后的有毒有机物如何作用于ARGs的复制和表达,这应是未来深化有毒有机物影响ARGs横向迁移机制的一个关键所在。 相似文献
13.
Transfer of genes between plant species has played an important role in crop improvement for many decades. Useful traits such as resistance to disease, insects, and stress have been transferred to crop varieties from noncultivated plants. Recombinant DNA methods greatly extend (even outside the plant kingdom) the sources from which genetic information can be obtained for crop improvement. Gene transfer systems based on recombinant DNA are available for several crop species and are under development for others. The concerted use of traditional and more recent methods for plant genetic manipulation will contribute to crop improvement. 相似文献
14.
Graphite: a mimic for DNA and other biomolecules in scanning tunneling microscope studies 总被引：11，自引：0，他引：11
Highly ordered pyrolytic graphite (HOPG) is the substrate often used in scanning tunneling microscope (STM) studies of biomolecules such as DNA. All of the images presented in this article are of freshly cleaved HOPG surfaces upon which no deposition has occurred. These images illustrate features previously thought to be due to biological molecules, such as periodicity and meandering of "molecules" over steps. These features can no longer be used to distinguish real molecules from features of the native substrate. The feasibility of the continued use of HOPG as a substrate for biological STM studies is discussed. 相似文献
15.
Weller GR Kysela B Roy R Tonkin LM Scanlan E Della M Devine SK Day JP Wilkinson A d'Adda di Fagagna F Devine KM Bowater RP Jeggo PA Jackson SP Doherty AJ 《Science (New York, N.Y.)》2002,297(5587):1686-1689
In eukaryotic cells, double-strand breaks (DSBs) in DNA are generally repaired by the pathway of homologous recombination or by DNA nonhomologous end joining (NHEJ). Both pathways have been highly conserved throughout eukaryotic evolution, but no equivalent NHEJ system has been identified in prokaryotes. The NHEJ pathway requires a DNA end-binding component called Ku. We have identified bacterial Ku homologs and show that these proteins retain the biochemical characteristics of the eukaryotic Ku heterodimer. Furthermore, we show that bacterial Ku specifically recruits DNA ligase to DNA ends and stimulates DNA ligation. Loss of these proteins leads to hypersensitivity to ionizing radiation in Bacillus subtilis. These data provide evidence that many bacteria possess a DNA DSB repair apparatus that shares many features with the NHEJ system of eukarya and suggest that this DNA repair pathway arose before the prokaryotic and eukaryotic lineages diverged. 相似文献
16.
Paulson S Helser A Nardelli MB Taylor RM Falvo M Superfine R Washburn S 《Science (New York, N.Y.)》2000,290(5497):1742-1744
The transfer of electrons from one material to another is usually described in terms of energy conservation, with no attention being paid to momentum conservation. Here we present results on the junction resistance between a carbon nanotube and a graphite substrate and show that details of momentum conservation also can change the contact resistance. By changing the angular alignment of the atomic lattices, we found that contact resistance varied by more than an order of magnitude in a controlled and reproducible fashion, indicating that momentum conservation, in addition to energy conservation, can dictate the junction resistance in graphene systems such as carbon nanotube junctions and devices. 相似文献
17.
beta-Glucuronidase catalyzed hydrolysis of benzo(a)pyrene-3-glucuronide and binding to DNA 总被引：1，自引：0，他引：1
beta-Glucuronidase catalyzes the hydrolysis of benzo[a]pyrene-3-glucuronide to 3-hydroxybenzo[a]pyrene. During the enzymatic hydrolysis, a benzo[a]pyrene derivative is formed which binds to DNA to a far greater extent than either the 3-hydroxybenzo[a]pyrene or its glucuronide. These results suggest that conjugates of benzo(a)pyrene may be converted by beta-glucuronidase at intracellular and organ sites distal to the initial sites of oxygenation and conjugation of benzo(a)pyrene to activated intermediates that are possibly carcinogenic. 相似文献
18.
3种DNA提取方法对养殖池塘不同生境菌群PCR-DGGE分析的影响 总被引：2，自引：0，他引：2
比较3种DNA提取方法(溶菌酶法、CTAB法及珠磨法)对养殖池塘几种生境(底泥、饲料、草鱼肠道内容物及肠道壁)菌群PCR-DGGE分析的影响。结果表明,以3种提取方法获得的DNA为模板均能进行16S rDNA V3区特异性片段扩增;但不同DNA提取方法对池塘不同生境菌群DGGE指纹图谱存在显著影响。DGGE指纹图谱显示草鱼肠道内容物菌群(溶菌酶法)与肠道壁菌群(溶菌酶法)存在较高一致性,底泥菌群(CTAB法)及饲料菌群(溶菌酶法)与鱼体肠道菌群(包括内容物菌群和肠道壁菌群)则存在明显差异,但肠道菌群与底泥菌群的相似度相对更高。研究提示采用微生物分子生态学工具对养殖池塘不同生境进行菌群结构分析时,需提前优化DNA提取方法;在以投饲为主的养殖鱼塘中,草鱼肠道菌群更多源自于池塘底泥。 相似文献
19.
When a mammalian cell strain was incubated with 5-iododeoxyuridine and 5-bromodeoxyuridine, DNA thymine was partially replaced by the halogen-containing pyrimidines. The extent of incorporation of the unnatural bases increased when amethopterin and hypoxanthine were added to the medium. It is thus evident that the replacement of DNA thymine by selected structural analogs, a phenomenon previously reported for bacterial systems, is applicable to cells of higher organisms. 相似文献
20.
Pan X Lührmann A Satoh A Laskowski-Arce MA Roy CR 《Science (New York, N.Y.)》2008,320(5883):1651-1654
Specialized secretion systems are used by many bacteria to deliver effector proteins into host cells that can either mimic or disrupt the function of eukaryotic factors. We found that the intracellular pathogens Legionella pneumophila and Coxiella burnetii use a type IV secretion system to deliver into eukaryotic cells a large number of different bacterial proteins containing ankyrin repeat homology domains called Anks. The L. pneumophila AnkX protein prevented microtubule-dependent vesicular transport to interfere with fusion of the L. pneumophila-containing vacuole with late endosomes after infection of macrophages, which demonstrates that Ank proteins have effector functions important for bacterial infection of eukaryotic host cells. 相似文献