超螺旋DNA的碱变构研究

对超螺旋ＤＮＡ（ＤＮＡＩ）的碱处理产物进行了琼脂糖凝胶电泳,氯化铯－溴化惭锭密度梯度超离心分析,紫外吸收光谱分析和电镜观察,实验结果表明超螺旋ＤＮＡ在碱性环境中的结构改变发生在很窄的ＰＨ范围内（ＰＨ１２．８８－１３．００）。超过ＰＨ临界点的ＣｓＣｌ－ＥＢ密度梯度超离心听高密度区形成稳定的区带。用透射电镜的观察表明碱变构的超螺旋ｐＢＲ３２２ＤＮＡ具有高电子密度并呈中空颗粒状,以上事实表明,ＤＮＡ在高     

λ-DNA Hind Ⅲ 经酸变性-复性形成变异形态

对λ噬菌体ＤＮＡ Ｈｉｎｄ Ⅲ 依次进行了酸变性、复性、ＤＮａｓｅ Ⅰ降解处理。处理后的混合物的柱层析色谱显示出一个抗ＤＮａｓｅ Ⅰ酶切的产物的微弱吸收峰。原子力显微术（ＡＦＭ）研究的结果表明,该产物是一种变异形态的ＤＮＡ,其长度介于对应的双螺旋ＤＮＡ的Ａ构象长度和Ｂ构象长度之间,高度（平均６．８１ｎｍ）则为双螺旋ＤＮＡ的测量高度的１３倍,分析和对照实验均说明该变异形态ＤＮＡ不是超螺旋结构,因而极     

红树DNA的十六烷基三甲基溴化铵法提取及其随机扩增多态DNA反应

采用ＣＴＡＢ法提取了耐盐植物红树ＤＮＡ,所得ＤＮＡ样品的紫外吸收Ａ２５８／Ａ２８０比值为１．８９,纯度能符合限制性内切酶酶切、ＰＣＲ反应以及ＤＮＡ重组克隆等分子生物学操作的要求．方法简便,容易掌握,较普通的酚－氯仿法有明显的优点．还探讨了以ＣＴＡＢ法制备的红树ＤＮＡ为模板进行ＲＡＰＤ反应参数的优化组合     

电离辐射诱导DNA链断裂的动力学研究

通过测试γ射线辐照下超螺旋ｐＢＲ３２２ ＤＮＡ分子单链断裂（ＳＳＢ）,双链剂量效应,得到ＳＳＢ、αＤＳＢ产额与ＤＮＡ现含一定浓度甘露醇的ＤＮＡ溶液体系中,Ｇ（ＳＳＢ）、Ｇ（αＤＳＢ）的例数与ｃ（ＤＮＡ）的倒数成线性关系,并以二级动力学描述了ＤＮＡ和甘露醇分子对．ＯＨ的竞争反应,得到．ＯＨ引起ＳＳαＤＳＢ的速率常数及其效率。     

细胞电穿孔导入DNA的动态特征

本文以Ｅ．ＣｏｌｉＨＢ１０１为模型细胞,研究了不同幅度和时间常数的ＲＣ放电脉冲条件下,触发细胞穿孔,导入长度分别为４２２和１６８０ｎｍ的超螺旋长丝形质粒ｐＵＣ－１８和ｐＣＰ１０,及精胺缩合后直径为８８ｎｍ的复曲面体的质粒ｐＣＰ１０,测定了相应的细胞转化率。实验结果显示了细胞电穿孔导入ＤＮＡ的动态特征。     

香蕉束顶病毒基因克隆和序列分析

对香蕉束顶病毒（ＢＢＴＶ）中国分离株ＤＮＡ组份Ｉ（ＤＮＡ－１）、外壳蛋白（ＣＰ）和运转蛋白（ＭＰ）基因进行了克隆和序列分析。ＢＢＴＶＤＮＡ－１含有１１０３个核苷酸,与南太平洋和亚洲分离株分别有８７％－８８％ ９６．９－９８％的核苷酸序列同源性。由ＤＮＡ－１编码的复制酶含有１８６个在酸残基。与南太平洋和亚洲分离株分别有８４．４％－９５．８％和９７．６％、９８．０％的氨基酸序列同源性。外壳蛋白基因由５     

乙型肝炎免疫指标全阴的原发性肝细胞癌患者体内HBV—DNA的检测…

本文以聚合酶链式反应（ＰＣＲ）对３５例乙型肝炎免疫指标（ＨＢＶｍ）全阴性的原发性肝细胞癌（ＰＨＣ）患者血清,外周血单核细胞（ＰＢＭＣ）肝活检标本进行乙型肝炎病毒ＨＢＶ－ＤＮＡ检测,其检出率分别为３４．２９％,６０．００％,６８．５７％,说明一部分血清ＨＢＶｍ全阴性的ＰＨＣ患者血清并非无传染性,ＥＬＳＩＡ法具有一定局限性。ＰＢＭＣ内有相当的ＨＢＶ－ＤＮＡ存在,这对于研究ＰＨＣ患者体内ＨＢＶ的存在情况     

产黑色素类厌氧杆菌质粒DNA的分离提取

采用碱解法从１１株产黑色素类厌氧杆菌（Ｂｌａｃｋ－Ｐｉｇｍｅｎｔｅｄ Ａｎａｒｏｂｉｃ Ｂｏｄ,简称ＢＰＡＢ）中提取其质粒ＤＮＡ,其中５株有质粒ＤＮＡ,其分子量大小不等,有的有超螺旋、开环、闭环三种结构,有的只有开环一种结构,对这几株细茵质粒ＤＮＡ的深入研究,可为令后将该质粒作为载体用于基因工程奠定基础。     

安徽庐江鸭乙型肝炎病毒LJ-76转染细胞系的建立

为建立鸭乙型肝炎病毒ＬＪ－７６的转染细胞系,将ＬＪ－７６病毒ＤＮＡ插入到ｐＵＣ１９的ＥｃｏＲⅠ位点上,分离得到含有双拷贝ＬＪ－７６ＤＮＡ的重组质粒．通过磷酸钙沉淀方法,将经ＣｓＣｌ等密度离心纯化的ＬＪ－７６ＤＮＡ双体导入到人肝癌细胞ＢＥＬ７４０２中．收集转染细胞的培养液进行蔗糖密度梯度离心,所得沉淀经检测发现含有ＬＪ－７６ＤＮＡ并具有特异性ＤＨＢＶ内源性ＤＮＡ多聚酶活性;对上述样品通过ＤｏｔＥＩＡ检测ＤＨＢＶ核心抗原及表面抗原结果为阳性．Ｓｏｕｔｈｅｒｎｂｌｏｔ分析表明转染细胞内存在病毒ＤＮＡ复制中间体ｃｃｃＤＮＡ、ｓｓＤＮＡ和ｒｃＤＮＡ,而ｃｃｃＤＮＡ被认为是复制活动较为活跃的标志．电镜观察转染细胞的上清发现有病毒颗粒的存在．     

水稻线粒体DNA的提取与分析

为了研究水稻细胞质雄性不育的分子基础,我们比较了各种提取线粒体ＤＮＡ（ｍｔＤＮＡ）的方法,并提出了一些改进措施。以丛广４１Ａ、丛广４１Ｂ和杂种一代广优青为材料,对所提取的材料ｍｔＤ－ＮＡ进行了紫外扫描、ＯＤ值测定、电泳、酶切等分析,结果表明,以新鲜材料进行不连续蔗糖密度梯度超速离心对提取高纯度的线粒体ＤＮＡ效果较好。     

Visualization of alkali-denatured supercoiled plasmid DNA by atomic force microscopy

To study the alkali denaturation of supercoiled DNA, plasmid pBR322 was treated with gradient concentrations of NaOH solution. The results of gel electrophoresis showed that the alkali denaturation of the supercoiled DNA occurred in a narrow range of pH value (12.88-12.90). The alkali-denatured supercoiled DNA ran, as a sharp band, faster than the supercoiled DNA. The supercoiled plasmid DNA of pBR322, pACYC184 and pJGX15A were denatured by NaOH, and then visualized by atomic force microscopy. Compared with the supercoiled DNA, the atomic force microscopy images of the alkali-denatured supercoiled DNA showed rough surface with many kinks, bulges on double strands with inhomogeneous diameters. The apparent contour lengths of the denatured DNA were shortened by 16%, 16% and 50% for pBR322, pACYC184 and pJGX15A, respectively. All evidence suggested that the alkali-denatured supercoiled DNA had a stable conformation with unregistered, topologically constrained double strands and intrastrand secondary structure.     

Nucleosome “phasing” and cruciform structures in circular supercoiled pBR322 DNA

Cruciform structures have been detected in pBR322 supercoiled DNA, both in its naked state and when complexed with histone octamer, using S1 endonuclease cleavage and EcoRI restriction. An inspection of the DNA sequence shows that the S1-hypersensitive sites are very near to AT-rich regions of pBR322 genome. A nucleosome “phasing” in these regions, as found on AT-rich regions of SV40 DNA (15), has been shown by restriction enzymes analysis. On the basis of these results it can be proposed that cruciform structures protrude on the nucleosome surface. This model explains the reason why these structures, which need high superhelical density, can exist in supercoiled DNA partially relaxed by nucleosome formation.     

Nucleosome "phasing" and cruciform structures in circular supercoiled pBR322 DNA

Cruciform structures have been detected in pBR322 supercoiled DNA, both in its naked state and when complexed with histone octamer, using S1 endonuclease cleavage and EcoRI restriction. An inspection of the DNA sequence shows that the S1-hypersensitive sites are very near to AT-rich regions of pBR322 genome. A nucleosome "phasing" in these regions, as found on AT-rich regions of SV40 DNA (15), has been shown by restriction enzymes analysis. On the basis of these results it can be proposed that cruciform structures protrude on the nucleosome surface. This model explains the reason why these structures, which need high superhelical density, can exist in supercoiled DNA partially relaxed by nucleosome formation.     

Supercondensed structure of plasmid pBR322 DNA in an Escherichia coli DNA topoisomerase II mutant

An unusual structural component, supercondensed pBR322 DNA, has been found in plasmid pBR322 DNA samples isolated from a DNA topoisomerase II mutant of Escherichia coli, SD108 (topA+, gyrB225). The supercondensed pBR322 DNA moved faster than supercoiled pBR322 DNA as a homogeneous band in agrose gels when the DNA samples were analysed by electrophoresis. The mobility of the supercondensed DNA was not substantially affected by chloroquine intercalation. The supercondensed pBR322 DNA migrated as a high density "third DNA band" when the samples were subjected to caesium chloride/ethidium bromide gradient equilibrium centrifugation. The unusual pBR322 DNA visualized by electron microscopy was a globoid-shaped particle. These observations suggest that the pBR322 plasmid can assume a tertiary structure other than a supercoiled or relaxed structure. DNA topoisomerases may be involved in the supercondensation of plasmid DNA and chromosomal DNA.     

Escherichia coli Fpg protein and UvrABC endonuclease repair DNA damage induced by methylene blue plus visible light in vivo and in vitro.

pBR322 plasmid DNA was treated with methylene blue plus visible light (MB-light) and tested for transformation efficiency in Escherichia coli mutants defective in either formamidopyrimidine-DNA glycosylase (Fpg protein) and/or UvrABC endonuclease. The survival of pBR322 DNA treated with MB-light was not significantly reduced when transformed into either fpg-1 or uvrA single mutants compared with that in the wild-type strain. In contrast, the survival of MB-light-treated pBR322 DNA was greatly reduced in the fpg-1 uvrA double mutant. The synergistic effect of these two mutations was not observed in transformation experiments using pBR322 DNA treated with methyl methanesulfonate, UV light at 254 nm, or ionizing radiation. In vitro experiments showed that MB-light-treated pBR322 DNA is a substrate for the Fpg protein and UvrABC endonuclease. The number of sites sensitive to cleavage by either Fpg protein or UvrABC endonuclease was 10-fold greater than the number of apurinic-apyrimidinic sites indicated as Nfo protein (endonuclease IR)-sensitive sites. Seven Fpg protein-sensitive sites per PBR322 molecule were required to produce a lethal hit when transformed into the uvrA fpg-1 mutant. These results suggest that MB-light induces DNA base modifications which are lethal and that these modifications are repaired by Fpg protein and UvrABC endonuclease in vivo and in vitro. Therefore, one of the physiological functions of Fpg protein might be to repair DNA base damage induced by photosensitizers and light.     

Strand cleavage of supercoiled DNA by water-soluble peroxyl radicals. The overlooked importance of peroxyl radical charge

It is well established that the peroxyl radicals formed during the thermal decomposition of 2,2'-azobis(amidinopropane), ABAP, in oxygenated water can cleave double-stranded DNA, from which fact it has been concluded that peroxyl radicals, as a general class, can induce DNA strand scission. However, the ABAP-derived radicals are positively charged, and DNA is a negatively charged polyanion. Moreover, the relatively small and, therefore, free to diffuse peroxyl radicals likely to be formed in vivo will generally be negatively charged or neutral. Plasmid supercoiled DNA [pBR 322, 4361 base pairs (bp)] was reacted with known, equal fluxes of two positively charged peroxyl radicals, a negatively charged peroxyl radical, and a neutral peroxyl radical. The two positively charged peroxyl radicals degraded >/=80% of the supercoiled pBR 322 at a flux of 4 radicals/bp, but the negatively charged and neutral peroxyl radicals had no significant effect even at a flux as high as 24 radicals/bp. The same lack of effect on the DNA was also observed with high fluxes of superoxide/hydroperoxyl radicals. Similar results were obtained with another supercoiled DNA, pUC 19, except that pUC 19 is somewhat more sensitive to strand scission by positively charged peroxyl radicals than pBR 322. We conclude that most of the peroxyl radicals likely to be formed in vivo have little or no ability to induce DNA strand scission and that the potential role of electrostatics in radical/DNA reactions should always be considered.     

Nickel(II) and cobalt(II) complexes of hydroxyl-substituted triazamacrocyclic ligand as potential antitumor agents

The stability constants for the formation of nickel(II) and cobalt(II) complexes of the ligand [1,4,7]triazecan-9-ol (L) were presented. Antitumor activity of two complexes was reported. Nuclei of [NiL]-stimulated BEL-7402 cells clearly exhibited condensation and break down into chromatin clumps typical of apoptosis. Also it exhibited perturbation effects to cell cycle, and optimal induction of apoptosis was found by Flow-Cytometric analysis. But CoL complex did not exhibit introduction effects to BEL-7402 cells apoptosis; and could not perturb cell cycle. NiL and CuL complexes could cleave supercoiled DNA (pBR 322 DNA) to nicked and linear DNA, and DNA of cells treated with NiL or CuL complex was obviously damaged; while CoL complex only could cleave supercoiled DNA (pBR 322 DNA) to nicked DNA, and DNA of cells treated with CoL complex had no significant difference with control.     

Direct observation of positive supercoils introduced by reverse gyrase through atomic force microscopy

Reverse gyrase is a hyperthermophilic enzyme that can introduce positive supercoiling in substrate DNA. It is showed in our studies that positive DNA supercoils were induced in both pBR322 vector and an artificially synthesized mini-plasmid DNA by reverse gyrase. The left-handed structures adopted by positively supercoiled DNA molecules could be identified from their right-handed topoisomers through atomic force microscopic examination. Additional structural comparisons revealed that positively supercoiled DNA molecule AFM images exhibited increased contour lengths. Moreover, enzymatic assays showed that the positively supercoiled DNA could not be cleaved by T7 endonuclease. Together, this suggests that the overwound structure of positive supercoils could prevent genomic duplex DNA from randomly forming single-stranded DNA regions and intra-stranded secondary structures.     

DNA topoisomerase I mutants. Increased heterogeneity in linking number and other replicon-dependent changes in DNA supercoiling

Plasmid pBR322 DNA isolated from Salmonella typhimurium supX (topoisomerase I) mutants exhibits a novel supercoiling distribution characterized by extreme heterogeneity in linking number and the presence of highly negatively supercoiled topoisomers. The most negatively supercoiled topoisomers isolated from one supX mutant have more than twice the wild-type level of supercoiling; the distribution as a whole has a median superhelix density about 1.3 times that of wild type. Surprisingly, the supercoiling distribution of plasmid pUC9 DNA isolated from supX mutants differs from that of pBR322. Escherichia coli topoisomerase I mutants have been shown to acquire compensatory mutations that reduce bacterial chromosome supercoiling to below the wild-type level even in the absence of topoisomerase I. We find that such a compensatory mutation in an E. coli topoisomerase I deletion mutant does not reduce pBR322 DNA supercoiling to a level below that of wild type. Thus, the effects of topoisomerase mutations on supercoiling depend on the replicon.