<title>Effect of bending strain on the torsion constant of DNA</title>

Abstract

The torsion constants of both linear and circular forms of the same approximately 200 base- pair DNA were measured by time-resolved fluorescence polarization anisotropy (FPA). Upon circularization, the torsion constant undergoes a substantial increase, and the circular dichroism (CD) spectrum indicates a significant perturbation of the secondary structure. The torsion constant of the circular form lies in the range of values determined previously for similarly small circular DNAs by static methods. It is suggested that the long-standing discrepancy between torsion constants obtained via static methods for small circles and those obtained via the FPA method for linear DNAs may be due to such an alteration of the secondary structure and enhancement of the torsion constant by coherent bending strain present in the small circles.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.