共查询到20条相似文献，搜索用时 15 毫秒
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The structure of an RNA polymerase II-transcribing complex has been determined in the posttranslocation state, with a vacancy at the growing end of the RNA-DNA hybrid helix. At the opposite end of the hybrid helix, the RNA separates from the template DNA. This separation of nucleic acid strands is brought about by interaction with a set of proteins loops in a strand/loop network. Formation of the network must occur in the transition from abortive initiation to promoter escape. 相似文献
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Numerous agents attack DNA, forming lesions that impair normal replication. Specialized DNA polymerases transiently replace the replicative polymerase and copy past lesions, thus generating mutations, the major initiating cause of cancer. We monitored, in Escherichia coli, the kinetics of replication of both strands of DNA molecules containing a single replication block in either the leading or lagging strand. Despite a block in the leading strand, lagging-strand synthesis proceeded further, implying transient uncoupling of concurrent strand synthesis. Replication through the lesion requires specialized DNA polymerases and is achieved with similar kinetics and efficiencies in both strands. 相似文献
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Damage induced by ultraviolet light or x-rays to the DNA of a eucaryotic organism, Tetrahymena pyriformis, is repaired by a process similar to the repair system present in bacteria. This repair process, which involves defect excision and subsequent resynthesis of the damaged section of DNA, occurs in the dark. Photoreactivation of damage induced by ultraviolet light is also indicated by a reduction in observed repair synthesis. An improved method for detecting repair synthesis is described. Repair synthesis is measured in parental DNA strands isolated from cultures that have undergone normal DNA replication after the repair process. 相似文献
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Transcription of nonrepeated DNA in mouse brain 总被引：10，自引：0，他引：10
Under normal conditions of DNA renaturation, about 60 percent of mouse DNA fragments renature at a rate consistent with their being present only once per sperm. These nonrepeated sequences (also called single-copy or unique) may be used in RNA-DNA hybridization experiments to provide quantitative estimates of RNA diversity. About 10 percent of the mouse single-copy sequences are transcribed in mouse brain tissue. Estimates of about 3 percent were obtained for mouse liver and kidney RNA's. If only one of the complementary DNA strands is transcribed, this hybridization value implies that the equivalent of at least 300,000 different sequences of 1000 nucleotides are expressed in mouse brain tissue. It is suggested that the large amount of DNA in mammals is functionally important, and that a substantial proportion of the genome is expressed in the brain. 相似文献
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Abdurashidova G Deganuto M Klima R Riva S Biamonti G Giacca M Falaschi A 《Science (New York, N.Y.)》2000,287(5460):2023-2026
The initiation sites of bidirectional synthesis at the DNA replication origin located at the 3' end of the human lamin B2 gene were investigated. RNA-primed nascent DNA molecules were subjected to second-strand synthesis with appropriate primers, amplified by ligation-mediated polymerase chain reaction, and size fractionated. Evidence for precise start sites was obtained. Exploration of close to 1 kilobase, coupled to inhibition of Okazaki fragment synthesis, demonstrates that the leading strands initiate at precise nucleotides on either helix, overlapping by three base pairs, within the area bound to a protein complex possibly analogous to the prereplicative complex of yeast. 相似文献
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Mammalian mitochondrial DNA (mtDNA) replication has long been considered to occur by asymmetric synthesis of the two strands, starting at the multiple origins of the strand-displacement loop (D-loop). We report the discovery of a major replication origin at position 57 in the D-loop of several human cell lines (HeLa, A549, and 143B.TK-) and immortalized lymphocytes. The nascent chains starting at this origin, in contrast to those initiated at the previously described origins, do not terminate prematurely at the 3' end of the D-loop but proceed well beyond this control point, behaving as "true" replicating strands. This origin is mainly responsible for mtDNA maintenance under steady-state conditions, whereas mtDNA synthesis from the formerly identified D-loop origins may be more important for recovery after mtDNA depletion and for accelerating mtDNA replication in response to physiological demands. 相似文献
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Short fragments from both complementary strands in the newly replicated DNA of bacteriophage SPP-1 总被引：3，自引：0，他引：3
Bacillus subtilis bacteriophage SPP-I has separable complementary DNA strands. Fragments of nascent DNA isolated a very short time after phage infection show that these short chains are complementary to both phage DNA strands, as observed by hybridization techniques. 相似文献
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Tetraplex formation of a guanine-containing nonameric DNA fragment 总被引：16，自引：0，他引：16
A combination of spectroscopic and calorimetric techniques has been used to characterize the structures formed by a family of short, guanine-containing DNA single strands of the form d[GGTTXTTGG], X = A, C, G, T. In 1 molar NaCl at low temperatures, these molecules do not behave like single strands, but rather exhibit properties consistent with tetraplex formation. The standard state enthalpies, entropies, and free energies for formation of each tetraplex have been measured, as have preliminary nuclear magnetic resonance (NMR) spectra. In 1 molar KCl, the melting behavior of the structure or structures is more complex than in 1 molar NaCl. This observation may be related to the recently proposed "sodium-potassium switch." 相似文献
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Multiplex DNA sequencing 总被引：32，自引：0，他引：32
The increasing demand for DNA sequences can be met by replacement of each DNA sample in a device with a mixture of N samples so that the normal throughput is increased by a factor of N. Such a method is described. In order to separate the sequence information at the end of the processing, the DNA molecules of interest are ligated to a set of oligonucleotide "tags" at the beginning. The tagged DNA molecules are pooled, amplified, and chemically fragmented in 96-well plates. The resulting reaction products are fractionated by size on sequencing gels and transferred to nylon membranes. These membranes are then probed as many times as there are types of tags in the original pools, producing, in each cycle of probing, autoradiographs similar to those from standard DNA sequencing methods. Thus, each reaction and gel yields a quantity of data equivalent to that obtained from conventional reactions and gels multiplied by the number of probes used. To date, even after 50 successive probings, the original signal strength and the image quality are retained, an indication that the upper limit for the number of reprobings may be considerably higher. 相似文献
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The replicating form of single-stranded DNA virus has been isolated in pure form by chromatography on columns of methylated albumin. Its buoyant density in CsCl and "melting temperature" are characteristic of a double stranded DNA structure containing 43 percent guanine-cytosine. The nearest neighbors to uridylate were compared in the RNA synthesized when replicating-form DNA and mature single-stranded DNA were employed as templates in an in vitro system. The mature DNA component of the replicating duplex does not serve as the sole source of complementary RNA. The results agree best with the assumption that both strands of the replicating form function as templates. It is important to note that this is contrary to the situation found in the intact cell where only one of the two strands appears to be transcribed into message. 相似文献
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利用RNA干扰在线生物学软件分析猪瘟病毒NS3基因,设计针对NS3基因不同位置的小发卡RNA(short hairpin RNA,shRNA)干扰序列(其结构特征为正链(19nt)-环(9nt)-负链(19nt))。化学合成这些序列,并退火连接为双链干扰片段,将双链干扰片段定向克隆到干扰载体中,构建重组载体pGene-NS3-1,pGene-NS3-2和pGene-NS3-3,转化DH5α大肠杆菌感受态细胞,对转化产物进行kan+筛选,碱裂解法提取重组质粒,将酶切鉴定为阳性的质粒测序。结果显示,双链干扰片段克隆方向正确,序列中未出现核苷酸的插入,缺失等突变现象。表明靶向猪瘟病毒NS3基因shRNA干扰载体构建成功。 相似文献
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Satellite DNA in constitutive heterochromatin of the guinea pig 总被引：8，自引：0，他引：8
Total DNA and DNA from the heterochromatin and euchromatin fractions of male guinea pig liver nuclei were analyzed by cesium sulfate-silver density-gradient centrifugation. Total DNA is composed of three components: a heavy satellite DNA, a main DNA of intermediate density, and a light satellite DNA. Heterochromatin DNA shows a fourfold enrichment in the satellite components while euchromatin DNA is relatively devoid of them. The strands of both satellite DNA's are separable by centrifugation in alkaline cesium chloride. Base analyses on the separate strands demonstrate that the two satellite DNA's represent different species. 相似文献
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The DNA binding domain of the rat liver nuclear protein C/EBP is bipartite 总被引：117，自引：0，他引：117
C/EBP is a rat liver nuclear protein capable of sequence-specific interaction with DNA. The DNA sequences to which C/EBP binds in vitro have been implicated in the control of messenger RNA synthesis. It has therefore been predicted that C/EBP will play a role in regulating gene expression in mammalian cells. The region of the C/EBP polypeptide required for direct interaction with DNA has been identified and shown to bear amino acid sequence relatedness with the product of the myc, fos, and jun proto-oncogenes. The arrangement of these related amino acid sequences led to the prediction of a new structural motif, termed the "leucine zipper," that plays a role in facilitating sequence-specific interaction between protein and DNA. Experimental tests now provide support for the leucine zipper hypothesis. 相似文献
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Bertone P Stolc V Royce TE Rozowsky JS Urban AE Zhu X Rinn JL Tongprasit W Samanta M Weissman S Gerstein M Snyder M 《Science (New York, N.Y.)》2004,306(5705):2242-2246
Elucidating the transcribed regions of the genome constitutes a fundamental aspect of human biology, yet this remains an outstanding problem. To comprehensively identify coding sequences, we constructed a series of high-density oligonucleotide tiling arrays representing sense and antisense strands of the entire nonrepetitive sequence of the human genome. Transcribed sequences were located across the genome via hybridization to complementary DNA samples, reverse-transcribed from polyadenylated RNA obtained from human liver tissue. In addition to identifying many known and predicted genes, we found 10,595 transcribed sequences not detected by other methods. A large fraction of these are located in intergenic regions distal from previously annotated genes and exhibit significant homology to other mammalian proteins. 相似文献
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The DNA-binding properties of the major regulatory protein alpha 4 of herpes simplex viruses 总被引：58，自引：0，他引：58
N Michael D Spector P Mavromara-Nazos T M Kristie B Roizman 《Science (New York, N.Y.)》1988,239(4847):1531-1534
The transition from the expression of alpha, the first set of five herpes simplex virus genes expressed after infection, to beta and gamma genes, expressed later in infection, requires the participation of infected cell protein 4 (alpha 4), the major viral regulatory protein. The alpha 4 protein is present in complexes formed by proteins extracted from infected cells and viral DNA fragments derived from promoter domains. This report shows that the alpha 4 protein forms specific complexes with DNA fragments derived from 5' transcribed noncoding domains of late (gamma 2) genes whose expression requires viral DNA synthesis as well as functional alpha 4 protein. Some of the DNA fragments to which alpha 4 binds do not contain homologs of the previously reported DNA binding site consensus sequence, suggesting that alpha 4 may recognize and interact with more than one type of DNA binding site. The alpha 4 proteins can bind to DNA directly. A posttranslationally modified form of the alpha 4 protein designated alpha 4c differs from the alpha 4a and alpha 4b forms with respect to its affinity for DNA fragments differing in the nucleotide sequences of the binding sites. 相似文献
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The success of nanorobotics requires the precise placement and subsequent operation of specific nanomechanical devices at particular locations. The structural programmability of DNA makes it a particularly attractive system for nanorobotics. We have developed a cassette that enables the placement of a robust, sequence-dependent DNA robot arm within a two-dimensional (2D) crystalline DNA array. The cassette contains the device, an attachment site, and a reporter of state. We used atomic force microscopy to demonstrate that the rotary device is fully functional after insertion. Thus, a nanomechanical device can operate within a fixed frame of reference. 相似文献
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DNA mismatch correction in a defined system 总被引：64，自引：0，他引：64
DNA mismatch correction is a strand-specific process involving recognition of noncomplementary Watson-Crick nucleotide pairs and participation of widely separated DNA sites. The Escherichia coli methyl-directed reaction has been reconstituted in a purified system consisting of MutH, MutL, and MutS proteins, DNA helicase II, single-strand DNA binding protein, DNA polymerase III holoenzyme, exonuclease I, DNA ligase, along with ATP (adenosine triphosphate), and the four deoxynucleoside triphosphates. This set of proteins can process seven of the eight base-base mismatches in a strand-specific reaction that is directed by the state of methylation of a single d(GATC) sequence located 1 kilobase from the mispair. 相似文献