A novel intact circular dsDNA supercoil
A novel intact circular dsDNA supercoil is proposed as an alternative to the conventional DNA supercoil, so that the two complementary strands of ssDNA circles are separable without any covalent bond breakage. This new structure can be visualized by using two tubings: one black and one clear. Twist the black tubing a number of times and connect its two ends. Do the same for the clear tubing. Then wrap the two tubings together. This forms the separable or novel supercoil. On the other hand, the conventional supercoil can be modeled by twisting the black and clear tubings together and then connect their respective ends, so that the two tubings are not separable unless one of them is cut. Experimentally, in the absence of any enzyme, many intact plasmid dsDNA circles give two bands on agarose gel electrophoresis under a certain given condition, while the same plasmid molecules after cutting once by a restriction enzyme give only one band under the same, condition. In the case of intact pUC19 plasmids, these two bands can then be, recovered and sequenced separately, using two primers in opposite directions. Each band gives mostly one sequence which is complementary to that of the other band. The combination of the above theoretical model and experimental results strongly suggests that there is an alternative structure of DNA which does not have the usual difficulty of unwinding, rewinding and requiring numerous covalent bond breakages and ligations during semiconservative replication.
Unable to display preview. Download preview PDF.
- Casey, J. and N. Davidson. 1977. Rates of formation and thermal stabilities of RNA:DNA and DNA:DNA duplexes at high concentrations of formamide.Nucl. Acids Res. 4, 1539–1552.Google Scholar
- Rich, A. 1995. The nucleic acids. A backward glance.Ann. NY Acad. Sci. 758, 97–142.Google Scholar
- Saenger, W. 1984.Principles of Nucleic Acid Structure New York: Springer-Verlag.Google Scholar
- Sambrook, J., E. F. Fritsch and T. Maniatis. 1989.Molecular Cloning, 2nd ed. Cold Spring Harbor, NY: Cold Spring Harbor Laboratory Press.Google Scholar
- Stasiak, A. 1996. Getting down to the core of homologous recombination.Science 272, 828–829.Google Scholar
- Wu, T. T. 1968a. Strandedness of DNA at 92% relative humidity.Bull. Math. Biophys. 30, 681–686.Google Scholar
- Wu, T. T. 1968b. Periodic conformations of deoxyribonucleic acids.Bull. Math. Biophys. 30, 687–700.Google Scholar
- Wu, T. T. 1969a. A model for the tertiary structure of transfer ribonucleic acid.Bull. Math. Biophys 31, 395–402.Google Scholar
- Wu, T. T. 1992. Intact double-stranded DNA plasmid molecules give two bands on agarose gel electrophoresis.FASEB J. 6, A223.Google Scholar
- Wu, T. T. 1993. Strand separation of supercoiled intact circular dsDNA.FASEB J. 7, A1289.Google Scholar