SYMMETRY LAWS FOR INTERACTION BETWEEN HELICAL MACROMOLECULES

The power of symmetry laws is applied in many scientific areas from el ementary particle physics to structural biology. The structures of man y biological helices, including DNA, were resolved with the use of per tinent symmetry constraints, It was not recognized, however, that simi lar constraints determine cardinal features of helix-helix interaction s vital for many recognition and assembly reactions in living cells. W e now formulate such symmetry-determined interaction laws and apply th em to explain DNA ''over-winding'' from 10.5 base pairs per turn in so lution to 10 in hydrated fibers, counterion specificity in DNA condens ation, and forces observed over the last 15 Angstrom of separation bet ween DNA, collagen, and four-stranded guanosine helices.