Abstract
Upon increasing the concentration of ethylene glycol (EG) at 37°C, the twist energy parameter, E~T~, which governs the supercoiling free energy, was recently found to undergo a decreasing (or reverse) sigmoidal transition with a midpoint near 20 w/v % EG. In this study, the effects of adding 20 w/v % EG on the torsion elastic constant (α) of linear p30δ DNA and on the hydrodynamic radius (R~H~) of a synthetic 24 bp duplex DNA were examined at both 40 and 20°C. The time‐resolved fluorescence intensity and fluorescence polarization anisotropy (FPA) of intercalated ethidium were measured in order to assess the effects of 20 w/v % EG on: (1) α; (2) R~H~; (3) the lifetimes of intercalated and non‐intercalated dye; (4) the amplitude of dye wobble in its binding site; and (5) the binding constant for intercalation. The effects of 20 w/v % EG on the circular dichroism (CD) spectrum of the DNA and on the emission spectrum of the free dye were also measured. At 40°C, addition of 20 w/v % EG caused a substantial (1.27‐ to 1.35‐fold) increase in α, a significant change in the CD spectrum, and a very small, marginally significant increase in R~H~, but little or no change in the amplitude of dye wobble in its binding site or the lifetime of intercalated dye. Together with previously reported measurements of E~T~, these results imply that the bending elastic constant of DNA is significantly decreased by 20 w/v % EG at 40°C. At 20°C, addition of 20 w/v % EG caused a marginally significant decrease in α and very little change in any other measured properties. Also at 20°C, addition of 30 w/v % betaine caused a marginally significant increase in α and significant but modest change in the CD spectrum, but very little change in any other properties. © 2006 Wiley Periodicals, Inc. Biopolymers 85: 222–232, 2007.
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