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Updated: Jul 19, 2026

Single-molecule Manipulation of G-quadruplexes by Magnetic Tweezers
Published on: September 19, 2017
Folding and unfolding of a giant duplex-DNA in a mixed solution with polycations, polyanions and crowding neutral
1Department of Bioengineering, National Cardiovascular Center Research Institute, 5-7-1 Suita, Osaka, 565-8565, Japan. kidoaki@res.ncvc.go.jp
Abstract:
To understand the conformational behavior of a giant duplex-DNA chain in a mixed solution with various biopolymers with different state of ionization, the higher-order structure of the DNA chain was analyzed with a fluorescence microscope in the presence of polycations (poly-arginine), polyanions (poly-glutamic acid), and neutral polymers (poly-ethylene glycol) as a model for cellular environment. Concentrated medium with neutral polymer induced the discrete folding transition of the DNA. At the threshold condition for the transition, addition of small amounts of either the polycation or the polyanion caused marked structural changes in the folded DNAs. Based on thermodynamic considerations on the experimental results, profile of free energy of a single giant DNA chain was depicted with respect to the size, or the expansion factor alpha, in the three-dimensional structure of the DNA. The effect of the neural crowding polymer on the degree of folding of a single giant DNA chain is discussed in a semi-quantitative manner.
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