DNA stiffening and elongation caused by the binding of ethidium bromide

Abstract

1. The relative change of DNA viscosity induced by binding of ethidium bromide molecules has been measured for three DNA samples of very different molecular weights. 2. The experiments have been interpreted in terms of changes of DNA contour length and persistence length. 3. These results have been compared with those derived for the proflavine-DNA complex from literature data. The binding of ethidium bromide and proflavine causes the same chain elongation of 2.7 A ̊ ligand molecule . The change of persistence length is considerably smaller for ethidium bromide, possibly on account of its hydrophobic substituents.