Supramolecular ordering of DNA in the cholesteric liquid crystalline phase: an ultrastructural study.

Aqueous solutions of 146-base pair DNA fragments form a cholesteric liquid crystalline phase in the range of about 160-290 mg/ml. We present a structural analysis of this phase by comparing the data obtained from polarizing and electron microscopy. This phase shows multiple aspects or "textures" which are presented and interpreted. They mainly depend on the orientation of the structure relative to the observation plane and on the nature, distribution, and amount of defects present in the phase. These defects are then analyzed with the two methods, and the molecular orientations can be defined precisely in their core. The biological interest of such structural analyses is discussed in relation with the understanding of chromatin structure and function.