[Enzymatic cleavage of superhelical DNA in a liquid crystal state]

Superhelical pBR322 DNA molecules form liquid-crystalline dispersions in water-salt solutions containing poly(ethyleneglycol). The formation of the liquid-crystalline dispersions from superhelical DNA molecules results in the appearance of two sites inside the DNA molecules that are split by Micrococcal nuclease. The first site of digestion does not differ from the standard site split by this enzyme in water-salt solutions, whereas the second one represents a new site specific only for the DNA molecules forming liquid-crystalline dispersions. Splitting of the DNA molecule through the first site is accompanied by formation of its linear form; splitting of a new site results in the formation of two linear DNA fragments with molecular masses equal to half of the initial DNA molecules. Enzyme digestion of superhelical DNA molecules forming liquid-crystalline dispersions induces a reformation of the "nonspecific" space organization of dispersions to the cholesteric one. A hypothetic model for packing of the superhelical DNA molecules inside liquid-crystalline dispersions and its transformation under enzyme action is suggested.