Regular superstructures of purified DNA in ethanolic solutions

Aqueous solutions of purified DNA from bacteriophage T7 were subjected to various concentrations of ethanol and visualized by electron microscopy. Compact, linear, unbranched particles with uniform diameters were found which have three distinct lengths, 3.04±0.04 μm, 0.69±0.01 μm and 0.159±0.014μm, with increasing diameters. An analysis of the observations revealed supercoils of first, second and third order for the above lengths. DNA supercoiling may be the consequence of dehydration by ethanol and drying and, in native chromatin, of dehydration by histone.