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1.
Miwi catalysis is required for piRNA amplification-independent LINE1 transposon silencing 总被引:1,自引:0,他引:1
Reuter M Berninger P Chuma S Shah H Hosokawa M Funaya C Antony C Sachidanandam R Pillai RS 《Nature》2011,480(7376):264-267
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Some plasmid DNAs, when maintained in wild-type Escherichia coli strains, form high levels of oligomeric species while others remain primarily monomers. One explanation of this observation is that the plasmids that do not form circular oligomers lack a DNA sequence necessary for the formation or maintenance of circular oligomeric species. Here we describe the isolation of segments of DNA from the E. coli genome and other sources that through a recA+ -dependent process: (1) stimulate the conversion of monomeric plasmids to different oligomeric forms, (2) stimulate the conversion of an oligomeric plasmid to a mixture of monomeric and different oligomeric forms, and (3) increase the frequency of recovery of figure-8 molecules. Both cis-acting and trans-acting elements were found. These elements seen to act by stimulating either the frequency of the recombination events that lead to the interconversion of different oligomeric plasmid DNA molecules or some process involved in the maintenance of newly-formed recombinant molecules. 相似文献
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Sequence of retrovirus provirus resembles that of bacterial transposable elements 总被引:104,自引:0,他引:104
The nucleotide sequences of the terminal regions of an infectious integrated retrovirus cloned in the modified lambda phage cloning vector Charon 4A have been elucidated. There is a 569-base pair direct repeat at both ends of the viral DNA. The cell-virus junctions at each end consist of a 5-base pair direct repeat of cell DNA next to a 3-base pair inverted repeat of viral DNA. This structure resembles that of a transposable element and is consistent with the protovirus hypothesis that retroviruses evolved from the cell genome. 相似文献
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An exonucleolytic activity of human apurinic/apyrimidinic endonuclease on 3' mispaired DNA 总被引:3,自引:0,他引:3
Human apurinic/apyrimidinic endonuclease (APE1) is an essential enzyme in DNA base excision repair that cuts the DNA backbone immediately adjacent to the 5' side of abasic sites to facilitate repair synthesis by DNA polymerase beta (ref. 1). Mice lacking the murine homologue of APE1 die at an early embryonic stage. Here we report that APE1 has a DNA exonuclease activity on mismatched deoxyribonucleotides at the 3' termini of nicked or gapped DNA molecules. The efficiency of this activity is inversely proportional to the gap size in DNA. In a base excision repair system reconstituted in vitro, the rejoining of nicked mismatched DNA depended on the presence of APE1, indicating that APE1 may increase the fidelity of base excision repair and may represent a new 3' mispaired DNA repair mechanism. The exonuclease activity of APE1 can remove the anti-HIV nucleoside analogues 3'-azido-3'-deoxythymidine and 2',3'-didehydro-2', 3'-dideoxythymidine from DNA, suggesting that APE1 might have an impact on the therapeutic index of antiviral compounds in this category. 相似文献
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射极跟随器输入电阻很高、输出电阻很低,使得其用途非常广泛。本文就射极跟随器作输入级和输出级时,对主放大器的电压放大倍数的影响,作出简单的剖析。 相似文献
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A major goal of molecular oncology is to identify means to kill cells lacking p53 function. Most current cancer therapy is based on damaging cellular DNA by irradiation or chemicals. Recent reports support the notion that, in the event of DNA damage, the p53 tumour-suppressor protein is able to prevent cell death by sustaining an arrest of the cell cycle at the G2 phase. We report here that adeno-associated virus (AAV) selectively induces apoptosis in cells that lack active p53. Cells with intact p53 activity are not killed but undergo arrest in the G2 phase of the cell cycle. This arrest is characterized by an increase in p53 activity and p21 levels and by the targeted destruction of CDC25C. Neither cell killing nor arrest depends upon AAV-encoded proteins. Rather, AAV DNA, which is single-stranded with hairpin structures at both ends, elicits in cells a DNA damage response that, in the absence of active p53, leads to cell death. AAV inhibits tumour growth in mice. Thus viruses can be used to deliver DNA of unusual structure into cells to trigger a DNA damage response without damaging cellular DNA and to selectively eliminate those cells lacking p53 activity. 相似文献
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Identification and comparison of two sequence elements that confer cell-type specific transcription in yeast 总被引:3,自引:0,他引:3
The MAT alpha 2 protein of budding yeast represses a set of genes; if the MATa1 protein is also present, a further set of genes is repressed. DNA sequence comparisons reveal a 20-base pair 'operator' sequence that is present in genes repressed by a1/alpha 2. A related, but distinct, sequence is found in genes repressed by alpha 2 alone. 相似文献
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The four-way (Holliday) DNA junction is the central intermediate in homologous recombination, a ubiquitous process that is important in DNA repair and generation of genetic diversity. The penultimate stage of recombination requires resolution of the DNA junction into nicked-duplex species by the action of a junction-resolving enzyme, examples of which have been identified in a wide variety of organisms. These enzymes are nucleases that are highly selective for the structure of branched DNA. The mechanism of this selectivity has, however, been unclear in the absence of structural data. Here we present the crystal structure of the junction-resolving enzyme phage T7 endonuclease I in complex with a synthetic four-way DNA junction. Although the enzyme is structure-selective, significant induced fit occurs in the interaction, with changes in the structure of both the protein and the junction. The dimeric enzyme presents two binding channels that contact the backbones of the junction's helical arms over seven nucleotides. These interactions effectively measure the relative orientations and positions of the arms of the junction, thereby ensuring that binding is selective for branched DNA that can achieve this geometry. 相似文献
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用自然科学定量方法实现对社会问题的描述,是计算机技术应用于社会分析与预测的关键.五元模糊计算模型源于五行学假设,摆脱用还原论方法对复杂系统建模的难度,是一种符合对立统一基本规律的、能引导计算向可持续方向发展的计算模型.以股市预测为证例,说明模型应用于实现社会宏观问题分析演化的可行性. 相似文献
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角色分配格中的特异元 总被引:1,自引:0,他引:1
Agent组织是合作求解的Agent集合,它描述了Agent与其承担的角色之间的关系.本文主要讨论Agent组织中的角色分配问题,提出了一种考虑了Role与Agent的偏好因素的扩充的角色分配二部图的概念,并指出Agent的角色分配问题就是在扩充的角色分配二部图上构造一个二部图的完美匹配.在Agent组织中,由于Agent及其组织的管理者都具有智能性,虽然Agent及其角色都可以得到匹配,但有些匹配不具有稳定性,因此自利的组织管理者和Agent都会在利益的驱动下背叛对方,从而导致组织破坏.紧接着本文讨论了稳定的扩充角色分配二部图的完美匹配集合,并在其上构造一个强稳定关系,从而将稳定匹配集和强稳定关系构造成一个代数结构--角色分配格,并在该格上构造了两个运算,并分析了两个运算之间的关系,由此得出角色分配格是一个分配格.最后分析了角色分配格中的几类特殊元--最大元、最小元、补元及交不可约元,并指出任何一个角色分配格都存在最大元和最小元,从而角色分配格是一个有界格,但并不是任何元都存在补元,从而角色分配格不一定是布尔代数,但是在给定特定的偏好下,即在特定的扩充角色分配二部图上,角色分配格可以构成布尔代数.对于交不可约元来说,它的重要意义就在于角色分配格中的任何元都可以表示成一些交不可约元的交,从而所有的交不可约元构成的集合是稳定匹配集的一个完备集.本文的结论是:扩充的角色分配二部图是Agent组织中的角色分配模型,其上所有的稳定匹配在强稳定关系下构成一个角色分配格,该格是一个有界分配格,但不一定是布尔代数,该格中的所有元都可以用其中的交不可约元来构造,从而为快速求解角色分配格做好了理论上的准备. 相似文献
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研究三株人癌细胞和两株对照细胞对细小病毒H-1杀伤作用敏感性的分子机制.表明了在感染复数moi(multipicityofinfection)为5pfu(plaqueformingunit)/细胞的情况下,作为H—1病毒复制受纳细胞的人肝癌细胞株OGY-7703和人胃癌细胞株SGC—7901,能够支持病毒DNA扩增和非结构蛋白NS—1基因的表达,这和作为阳性对照的由SV40转化的新生儿肾细胞株NB—K一样,但对H—1病毒感染有抗性的人肾癌细胞株OUR—10和它的对照人胎肾细胞株HuK—1,并不支持病毒DNA扩增和NS—1蛋白的表达.本文结果指出,细小病毒H—1的杀伤作用与细胞中的病毒DNA扩增及NS—1基因表达的程度相关. 相似文献
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八种稀土金属配合物和铂配合物抗HIV活性的研究 总被引:3,自引:0,他引:3
为了寻找治疗艾滋病的新药,研究了8种稀土金属(镧、铒、镝、钆、镨、镱、钐、钕)配合物和铂配合物的抗HIV活性。我们以C8166细胞系为指示细胞,测定样品对HIV-1IIIB诱导的细胞合胞体形成的抑制作用,并以MTT方法测定它们对细胞存活率的影响,以研究稀土和铂配合物对细胞的毒性。根据公式,计算出其CC50和EC50值,并进一步计算出其TI值。结果表明,镧配合物、钐配合物和铂配合物的EC50值分别为0.006μg/ml、74.28μg/ml和21.54μg/ml,它们的治疗指数分别为63、21和45,具有一定的抗HIV-1活性。其它的配合物具有很低或者不具有抗HIV-1活性。 相似文献
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Identification of genes that modify ataxin-1-induced neurodegeneration 总被引:55,自引:0,他引:55
Fernandez-Funez P Nino-Rosales ML de Gouyon B She WC Luchak JM Martinez P Turiegano E Benito J Capovilla M Skinner PJ McCall A Canal I Orr HT Zoghbi HY Botas J 《Nature》2000,408(6808):101-106
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目前我国已经进入了老龄化社会,老年人的健康问题深受关注。体育锻炼作为促进健康的重要作用得到了普遍认同。本文就老年人的科学锻炼问题提供了建议,借以提高老年人整体的健康水平。 相似文献
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司法公信力的结构性要素 总被引:7,自引:0,他引:7
司法公信力既具有公共权力的性质,也体现了人们对司法的信任和尊重的心理模态以及人民对司法的认同和信仰的程度。司法公信力的内涵可以通过分析其四个结构性要素:司法权威、司法独立、司法公正、司法信仰来予以阐明。 相似文献
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结合宪法的原则性规定,分析和探讨了公用征收必须具备为了公共利益的目的、遵循法律规定的程序、予以公正的补偿这三个法律要件,同时就解决我国公用征收制度中存在的问题提出了建议。 相似文献
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赵更吉 《西北师范大学学报(自然科学版)》2007,43(6):105-107
指出编辑过程中要注重“思”与“查”,要审视内容的正确性和合法合规性,要正确处理大局与局部、现实与过去和将来、整体与特例的关系,还要认真细心地去审查各个细节问题.只有如此,才能保证经手的文稿不出问题或少出问题. 相似文献
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In 1991, we found that methylation outside the Pvu II recognition sequence could partially inhibit its cleavage activity. To clarify the molecular mechanism, three plasmids with different methylation states were constructed. Then, together with the original one, four plasmids were digested with different amounts of Pvu II. Results show that methylation on both sites results in 90 % inhibition; moving the methylated site one base further away decreases the inhibitory effect to about 30 %; with the adjacent dam methylation site eliminated, the inhibitory effect disappears. The data suggest that the inhibition of cleavage activity caused by outside methylation is not “all or none”, and the degree of inhibition is dependent on the position and the number of methylated bases. 相似文献