An efficient and possibly general packing mode for crystals of B-DNA oligonucleotides

Two crystal forms of the self-complementary deoxytetramer GpGpCpC have been obtained by use of the phase diagram technique: hexagonal P6₂22 or P6₄22 with a = b = 67.7 Å, c = 105.6 Å, and trigonal P3₂12 or P3₁12 with a = b = 116.9 Å, c = 116.4 Å. Diffraction patterns from both crystals show strong 3.38 Å reflections that are typical of base-stacking in B-DNA. The self-rotation function R(φ, ψ, 180°) for the hexagonal form exhibits peaks representing pseudodyad rotation, whose periodicity also suggests B-DNA. Crystal packing arguments also favor use of this crystal form for a B helix.