Effects of ethylene glycol on the torsion elastic constant and hydrodynamic radius of p30[delta] DNA

• Published in: Biopolymers Vol. 85; no. 3; pp. 222 - 232
• Main Authors: Rangel, David P, Brewood, Greg P, Fujimoto, Bryant S, Schurr, JMichael
• Format: Journal Article
• Language: English
• Published: 01.01.2007
• ISSN: 0006-3525; 1097-0282
• DOI: 10.1002/bip.20634

Upon increasing the concentration of ethylene glycol (EG) at 37 not equal to , the twist energy parameter, E sub(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 ( alpha ) of linear p30[delta] DNA and on the hydrodynamic radius (R sub(H)) of a synthetic 24 bp duplex DNA were examined at both 40 and 20 not equal to . 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) alpha ; (2) R sub(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 not equal to , addition of 20 w/v % EG caused a substantial (1.27- to 1.35-fold) increase in alpha , a significant change in the CD spectrum, and a very small, marginally significant increase in R sub(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 sub(T), these results imply that the bending elastic constant of DNA is significantly decreased by 20 w/v % EG at 40 not equal to . At 20 not equal to , addition of 20 w/v % EG caused a marginally significant decrease in alpha and very little change in any other measured properties. Also at 20 not equal to , addition of 30 w/v % betaine caused a marginally significant increase in alpha and significant but modest change in the CD spectrum, but very little change in any other properties.