Supercoiled plasmid

The formation of three-stranded nucleic acid complexes was first demonstrated over five decades ago [56] but the possible biological role of an extended triplex was expanded by the discovery of the H-DNA structure in natural DNA samples [57-59]. H-DNA is an intermolecular triplex that is generally of the pyrimidine-purine x pyrimidine type ( dot -Watson-Crick pairing and cross Hoogsteen base paring) and can be formed at mirror repeat sequences in supercoiled plasmids [59]. 

Prazeres, D.M.F., Schluep, T., and Cooney, C., Preparative purification of supercoiled plasmid DNA using anion-exchange chromatography, ]. Chromatogr. A, 806, 31, 1998. 

Ferreira, G.N.M., Cabral, J.M.S., and Prazeres, D.M.F., Development of process flow sheets for the purification of supercoiled plasmids for gene therapy applications, Biotechnol. Prog. 15, 725, 1999. 

Giovanni, R., Freitag, R., and Tertnikova, T. B., High-performance membrane chromatography of supercoiled plasmid DNA, Anal. Chem., 70, 3348, 1998. 

In the absence of conclusive data on the role of a positive supercoiling wave, static positive supercoiling elicited by nucleosome reconstitution on relaxed or slightly positively-supercoiled plasmids [51] or by ethidium bromide intercalation in the loop of mononucleosomes on DNA minicircles [52] did not succeed either in releasing dimers. Moreover, circular dichroism, histone chemical modi-flcation and H3-thiol accessibility failed to detect an even slight alteration in the structure of such torsionally-stressed nucleosomes [51]. The reason was later found to lie in the ability of nucleosome entry/exit DNAs to form a positive crossing [52]. 

Marrot, L. and Agapakis-Causse, C. (2000) Differences in the photogenotoxic potential of two fluoroquinolones as shown in diploid yeast strain (Saccharomyces cerevisae) and supercoiled plasmid DNA. Mutation Research, 468, 1-9. 

FIGURE 24-13 Relaxed and supercoiled plasmid DNAs. The molecule in the leftmost electron micrograph is relaxed the degree of supercoiling increases from left to right. 

Detection of SSBs and DSBs with the Help of Supercoiled Plasmids... 

Figure 6.11 AFM images of (left) 1 nM supercoiled plasmid DNA (left) and (right) condensed blobs of 1 nM supercoiled plasmid DNA in the presence of 1 mM of calixarene 6.33a (n = 4). Each image is 2 X 2 pun. (Reproduced by permission of The Royal Society of Chemistry).

Separation of polynucleotides 259 Supercoiled plasmid DNA investigated as model... 

Direct Site-selective Scission of Supercoiled Plasmid DNA... 

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