Construction of large DNA segments in Escherichia coli

Recombinant DNA clones containing large pieces of DNA are useful in the study of large genetic units, but these are difficult to make in most bacterial cloning vectors. A strategy is described that uses general and site-specific recombination to construct large pieces of eukaryotic DNA from smaller cloned segments. The large clones are propagated on F factor-based plasmids in Escherichia coli. They can be easily modified to introduce mutations or rearrangements. These techniques were applied to the construction of large DNA segments from the bithorax complex of Drosophila.     

一种快速提取玉米大群体基因组DNA的方法

快速高效的DNA提取方法是玉米大规模分子育种的第一步,因此,需要发展一种快速提取玉米基因组DNA的方法,以满足我国中小型实验室的需要。本研究介绍了一种可用于玉米大规模基因组DNA提取的方法：先利用改良碱煮法提取玉米籽粒小块胚乳的DNA,进行基因型鉴定,对大群体进行筛选,再利用电钻磨样及简化的CTAB法快速提取玉米苗期叶片的DNA,进行后期的研究。这种方法使得玉米大群体的筛选和研究简单化、快速化、常规化,可广泛应用于玉米分子育种。     

用聚赖氨酸包被国产载玻片制作DNA芯片

用多聚赖氨酸对国产载玻片进行包被处理,在不同的固定条件下,比较其与进口多聚赖氨酸载玻片对大片段DNA和3′端氨基修饰寡核苷酸的固定效果.结果表明,在DNA固定率上,自行包被处理的国产载玻片与进口多聚赖氨酸载玻片没有显著差异;紫外交联对大片段DNA固定率影响显著,但对氨基修饰的寡核苷酸影响不显著;3种点样液中,进口点样液MSS点样效果最好,其次为3×SSC,第三是水.氨基修饰的寡核苷酸可以很好地固定在聚赖氨酸包被的载玻片上.     

真核生物重复序列的研究进展

真核生物核基因组内含有大量的DNA重复序列,在核基因组结构和功能研究中居于举足轻重的地位.本文主要介绍真核生物几类重要DNA重复序列的特点和用途,并对其在物种起源和进化、染色体分子指纹图谱绘制、分子标记辅助选择及染色体操作中的应用作了分析与介绍.     

Volatilization of high molecular weight DNA by pulsed laser ablation of frozen aqueous solutions

DNA has been volatilized by pulsed laser ablation of a thin film of a frozen aqueous DNA solution. The target film was irradiated in vacuum by a pulsed laser at power densities sufficient to ablate the ice matrix. The expanding ablated water vapor entrained embedded DNA molecules and expelled them into the gas phase. Ejection of DNA molecules as large as 410 kilodaltons was verified by collection of the ablation products and subsequent mass analysis by polyacrylamide gel electrophoresis with autoradiographic detection.     

Conserved structure for single-stranded telomeric DNA recognition

The essential Cdc13 protein in the yeast Saccharomyces cerevisiae is a single-stranded telomeric DNA binding protein required for chromosome end protection and telomere replication. Here we report the solution structure of the Cdc13 DNA binding domain in complex with telomeric DNA. The structure reveals the use of a single OB (oligonucleotide/oligosaccharide binding) fold augmented by an unusually large loop for DNA recognition. This OB fold is structurally similar to OB folds found in the ciliated protozoan telomere end-binding protein, although no sequence similarity is apparent between them. The common usage of an OB fold for telomeric DNA interaction demonstrates conservation of end-protection mechanisms among eukaryotes.     

Steps toward computer analysis of nucleotide sequences

Advances in recombinant DNA technology have allowed the isolation of large numbers of biologically interesting fragments of DNA. Concomitant improvements in methods for nucleic acid sequencing have led many investigators to characterize their clones by sequencing them. This has resulted in the accumulation of such large amounts of sequence data that computer-assisted methods, with programs directed toward the manipulation of nucleic acid sequences, have become indispensable during the collection and analysis of that data.     

Single-molecule kinetics of lambda exonuclease reveal base dependence and dynamic disorder

We used a multiplexed approach based on flow-stretched DNA to monitor the enzymatic digestion of lambda-phage DNA by individual bacteriophage lambda exonuclease molecules. Statistical analyses of multiple single-molecule trajectories observed simultaneously reveal that the catalytic rate is dependent on the local base content of the substrate DNA. By relating single-molecule kinetics to the free energies of hydrogen bonding and base stacking, we establish that the melting of a base from the DNA is the rate-limiting step in the catalytic cycle. The catalytic rate also exhibits large fluctuations independent of the sequence, which we attribute to conformational changes of the enzyme-DNA complex.     

Cyclobutane-type pyrimidine dimers in polynucleotides

The formation of cyclobutane-type dimers between adjacent pyrimidine residues in model polynucleotides or DNA may be represented by the general scheme See pdf 379.pdf Whereas the formation of all other known photoproducts follows the irreversible path See pdf 379.pdf Thus dimers are distinguished from other photoproducts by the fact that they can be monomerized, as well as formed, by ultraviolet irradiation. At large incident fluxes of photons the steady-state value of dimers depends on wavelength and pH, as well as on other characteristics of the surrounding medium. The number of dimers in an irradiated polynucleotide may be decreased by purely photochemical means, whereas this is not true for most other photoproducts, for which continued irradiation, irrespective of wavelength, always results in the formation of more photoproduct (37). The wavelength dependence of the steady-state for dimers is also reflected in the biological activity of irradiated transforming DNA. This experiment and the fact that photoreactivating enzyme plus visible light monomerizes dimers (and has not been demonstrated to have any effect on other photoproducts) are the strongest lines of experimental evidence that pyrimidine dimers of the cyclobutane type are biologically important lesions and can account for a large fraction of the effects of ultraviolet light on DNA in solution. Insofar as DNA is one of the more important biological structures, such dimers, when formed, account for a large part of the effects of ultraviolet radiation on biological systems.     

毛竹大片段双元细菌人工染色体基因组文库的构建

从毛竹Phyllostachys pubescens幼嫩叶片中提取纯化得到高质量的基因组DNA,经限制性内切酶BamH I对它们进行梯度酶切,脉冲场电泳选择合适酶切DNA片段,与脱磷酸化处理过的质粒载体pCLD04541按质量比3∶1相互连接,转化大肠杆菌Escherichia coli DH10B感受态细胞进行蓝白斑筛选,挑取白色克隆,获得重组率较高的阳性克隆,构建了含有10⁴个克隆的双元细菌人工染色体（BIBAC）基因组文库,并通过脉冲场电泳检测分析后确定,所构建的毛竹BIBAC文库平均插入片段为105 kb,约覆盖5倍毛竹基因组。该文库的构建为毛竹基因组研究做好了前期的基础工作。图8参18     

Chromosomal region of the cystic fibrosis gene in yeast artificial chromosomes: a model for human genome mapping

A general strategy for cloning and mapping large regions of human DNA with yeast artificial chromosomes (YAC's) is described. It relies on the use of the polymerase chain reaction to detect DNA landmarks called sequence-tagged sites (STS's) within YAC clones. The method was applied to the region of human chromosome 7 containing the cystic fibrosis (CF) gene. Thirty YAC clones from this region were analyzed, and a contig map that spans more than 1,500,000 base pairs was assembled. Individual YAC's as large as 790 kilobase pairs and containing the entire CF gene were constructed in vivo by meiotic recombination in yeast between pairs of overlapping YAC's.     

Retroviral DNA integration directed by HIV integration protein in vitro

Efficient retroviral growth requires integration of a DNA copy of the viral RNA genome into a chromosome of the host. As a first step in analyzing the mechanism of integration of human immunodeficiency virus (HIV) DNA, a cell-free system was established that models the integration reaction. The in vitro system depends on the HIV integration (IN) protein, which was partially purified from insect cells engineered to express IN protein in large quantities. Integration was detected in a biological assay that scores the insertion of a linear DNA containing HIV terminal sequences into a lambda DNA target. Some integration products generated in this assay contained five-base pair duplications of the target DNA at the recombination junctions, a characteristic of HIV integration in vivo; the remaining products contained aberrant junctional sequences that may have been produced in a variation of the normal reaction. These results indicate that HIV IN protein is the only viral protein required to insert model HIV DNA sequences into a target DNA in vitro.     

The genome sequence of Trypanosoma cruzi, etiologic agent of Chagas disease

Whole-genome sequencing of the protozoan pathogen Trypanosoma cruzi revealed that the diploid genome contains a predicted 22,570 proteins encoded by genes, of which 12,570 represent allelic pairs. Over 50% of the genome consists of repeated sequences, such as retrotransposons and genes for large families of surface molecules, which include trans-sialidases, mucins, gp63s, and a large novel family (>1300 copies) of mucin-associated surface protein (MASP) genes. Analyses of the T. cruzi, T. brucei, and Leishmania major (Tritryp) genomes imply differences from other eukaryotes in DNA repair and initiation of replication and reflect their unusual mitochondrial DNA. Although the Tritryp lack several classes of signaling molecules, their kinomes contain a large and diverse set of protein kinases and phosphatases; their size and diversity imply previously unknown interactions and regulatory processes, which may be targets for intervention.     

DNA疫苗制备工艺研究

以禽流感DNA疫苗pCAOH5转化大肠杆菌JM109后,利用发酵罐进行发酵培养。将菌体悬浮裂解中和后,经澄清和浓缩处理,利用阴离子交换色谱对其进行纯化。结果表明实验室规模的技术路线完全能够为质粒DNA的工业化制备奠定技术基础。     

棉花基因组DNA快速提取方法改良

选择2种简化的棉花基因组DNA提取方法并进行适当精简改良后与传统CTAB提取法进行实验对比的结果显示,改良SDS-CTAB法所提DNA得率较高,纯度好,但其操作步骤相对复杂。改良CTAB法操作更加简捷,但DNA得率相对较低,所得DNA溶液浑浊度较高。相对于传统的CTAB提取法,两种改良方法都能够更加快捷的得到足量且纯净的基因组DNA,完全能够满足转基因后代PCR筛选检测的要求。     

微卫星PCR聚丙烯酰胺凝胶银染法影响因素的分析研究

 微卫星PCR结合聚丙烯酰胺凝胶电泳是一种常用的DNA检测方法。此法分离小于500bP的DNA片段效果很好，分辨率极高，只相差1bp的片段也能分开，且可容纳相对大量的DNA。再结合银染法使该方法得到了广大科研工作着的青睐，本研究通过多方面摸索对该方法进行了总结和改良。     

同源重组探针在暂时转化的烟草原生质体内的重组和缺失

通过电激法(electroporation)将同源重组探针pBC 7导入烟草原生质体,再从转化的烟草原生质体中提取DNA,并将其转化到E.coli DH 1细胞.结果在E.codi DH 1细胞中获得了一种新的质粒分子,该质粒含有功能的neo基因,与重组探针pBC 7相比有较大的缺失、倒位,并出现了新的限制酶切部位,重组探针pBC 7的主要特征为含有Tn5的neo基因两个截短的不等部份,只有通过重排才可能产生完整的neo基因,这表明了暂时转化的原生质体在外源DNA整合以前具有这样的基因重排功能。     

DNA催化活性的研究：Ⅱ.DNA分子催化机理探讨

通过乙酸萘酯水解产物的显色反应，研究了ＤＮＡ分子二级结构对催化萘酯水解活性的重要性，结果表明：双链ＤＮＡ（ｄｓＤＮＡ）分子具有良好催化乙酸－α－萘酯、乙酸－β－萘酯水解的活性，而单链ＤＮＡ（ｓｓＤＮＡ）则完全不具备这种活性，ＤＮＡ完全酶解产物也不能使α－萘酯产生显色反应。因此认为，ＤＮＡ分子是具有催化活性的生物高分子。从ＤＮＡ二级结构角度探讨了其催化萘酯水解的反应机理。     

提高转HSA基因小鼠效率的研究

将无基因的序列CIT987SK-384D8(30号)和结构特异的内切酶基因hFEN1穴36号雪与HSA的cDNA(26号)进行混合注射来制备转HSA小鼠动物模型,旨在提高转HSA基因效率。结果表明:无基因的序列CIT987SK-384D8对HSA的整合基本无影响穴P>0.05雪,结构特异的内切酶基因hFEN1可以显著提高转HSA基因效率穴P<0.01雪。