CHIMERIC LIQUID CRYSTALLINITY - NONCOVALENT ASSOCIATION OF DNA AND BACTERIAL LEVAN

The liquid-crystalline phase of cell-free and nominally pure bacterial levan in water is shown to depend on the presence of DNA. The necessa ry concentrations of DNA are 2 orders of magnitude lower than those ne eded to stabilize a mesophase in aqueous solutions of DNA on its own a nd are similarly small in comparison to the number concentration of th e globular levan molecules. A partial phase diagram for liquid crystal linity in the ternary system water/levan/DNA, is mapped out. A model i s proposed in which the levan and DNA associate noncovalently, to prod uce supramolecular, rodlike aggregates. The term ''chimeric liquid cry stal'' is coined to denote a mesophase based on such rods assembled fr om otherwise unrelated molecular species. The model can account fur se veral characteristics of the liquid-crystalline phase of bacterial lev an, including the unexpected observation that liquid crystal phase for mation is accompanied by a continuous increase in viscosity.