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  • Phsyical and Biochemical Characterisation of DNA  (4)
  • Oxford University Press  (4)
  • American Institute of Physics (AIP)
  • Public Library of Science
  • 2010-2014  (4)
  • 1985-1989
  • 2013  (4)
  • 2010
  • 1
    Publication Date: 2013-05-29
    Description: Proteins that recognize and bind specific sites in DNA are essential for regulation of numerous biological functions. Such proteins often require a negative supercoiled DNA topology to function correctly. In current research, short linear DNA is often used to study DNA–protein interactions. Although linear DNA can easily be modified, for capture on a surface, its relaxed topology does not accurately resemble the natural situation in which DNA is generally negatively supercoiled. Moreover, specific binding sequences are flanked by large stretches of non-target sequence in vivo . Here, we present a straightforward method for capturing negatively supercoiled plasmid DNA on a streptavidin surface. It relies on the formation of a temporary parallel triplex, using a triple helix forming oligonucleotide containing locked nucleic acid nucleotides. All materials required for this method are commercially available. Lac repressor binding to its operator was used as model system. Although the dissociation constants for both the linear and plasmid-based operator are in the range of 4 nM, the association and dissociation rates of Lac repressor binding to the plasmid-based operator are ~18 times slower than on a linear fragment. This difference underscores the importance of using a physiologically relevant DNA topology for studying DNA–protein interactions.
    Keywords: Phsyical and Biochemical Characterisation of DNA
    Print ISSN: 0305-1048
    Electronic ISSN: 1362-4962
    Topics: Biology
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  • 2
    Publication Date: 2013-04-23
    Description: Electron transfer in DNA has been intensively studied to elucidate its biological roles and for applications in bottom-up DNA nanotechnology. Recently, mechanisms of electron transfer to DNA have been investigated; however, most of the systems designed are intramolecular. Here, we synthesized pyrene-conjugated pyrrole-imidazole polyamides (PPIs) to achieve sequence-specific electron injection into DNA in an intermolecular fashion. Electron injection from PPIs into DNA was detected using 5-bromouracil as an electron acceptor. Twelve different 5-bromouracil-containing oligomers were synthesized to examine the electron-injection ability of PPI. Product analysis demonstrated that the electron transfer from PPIs was localized in a range of 8 bp from the binding site of the PPIs. These results demonstrate that PPIs can be a useful tool for sequence-specific electron injection.
    Keywords: Phsyical and Biochemical Characterisation of DNA
    Print ISSN: 0305-1048
    Electronic ISSN: 1362-4962
    Topics: Biology
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  • 3
    Publication Date: 2013-11-02
    Description: Obtaining quantities of highly pure duplex DNA is a bottleneck in the biophysical analysis of protein–DNA complexes. In traditional DNA purification methods, the individual cognate DNA strands are purified separately before annealing to form DNA duplexes. This approach works well for palindromic sequences, in which top and bottom strands are identical and duplex formation is typically complete. However, in cases where the DNA is non-palindromic, excess of single-stranded DNA must be removed through additional purification steps to prevent it from interfering in further experiments. Here we describe and apply a novel reversed-phase ion-pair liquid chromatography purification method for double-stranded DNA ranging in lengths from 17 to 51 bp. Both palindromic and non-palindromic DNA can be readily purified. This method has the unique ability to separate blunt double-stranded DNA from pre-attenuated (n-1, n-2, etc) synthesis products, and from DNA duplexes with single base pair overhangs. Additionally, palindromic DNA sequences with only minor differences in the central spacer sequence of the DNA can be separated, and the purified DNA is suitable for co-crystallization of protein–DNA complexes. Thus, double-stranded ion-pair liquid chromatography is a useful approach for duplex DNA purification for many applications.
    Keywords: Phsyical and Biochemical Characterisation of DNA
    Print ISSN: 0305-1048
    Electronic ISSN: 1362-4962
    Topics: Biology
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  • 4
    Publication Date: 2013-11-02
    Description: The effect of a cationic-neutral diblock polypeptide on the conformation of single DNA molecules confined in rectangular nanochannels is investigated with fluorescence microscopy. An enhanced stretch along the channel is observed with increased binding of the cationic block of the polypeptide to DNA. A maximum stretch of 85% of the contour length can be achieved inside a channel with a cross-sectional diameter of 200 nm and at a 2-fold excess of polypeptide with respect to DNA charge. With site-specific fluorescence labelling, it is demonstrated that this maximum stretch is sufficient to map large-scale genomic organization. Monte Carlo computer simulation shows that the amplification of the stretch inside the nanochannels is owing to an increase in bending rigidity and thickness of bottlebrush-coated DNA. The persistence lengths and widths deduced from the nanochannel data agree with what has been estimated from the analysis of atomic force microscopy images of dried complexes on silica.
    Keywords: Phsyical and Biochemical Characterisation of DNA
    Print ISSN: 0305-1048
    Electronic ISSN: 1362-4962
    Topics: Biology
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