FORMATION OF (C-CENTER-DOT-G)ASTERISK-G TRIPLETS IN A B-DNA DUPLEX WITH OVERHANGING BASES

Crystallization of a DNA double helix with overhanging bases at the 5' -ends of both strands, results in the formation of two crystallographi cally independent (C . G)G triplets. In a previous report [Van Meerve lt, Vlieghe, Dautant, Gallois, Precigoux & Kennard (1995). Nature (Lon don), 374, 742-744] the unique molecular packing of the duplex and the Hoogsteen hydrogen-bond pattern and parallel backbone orientation of the guanine-containing strands in the triplets was described. The fine structural details and hydration of the d(GCGAATTCG) crystal structur e refined to 2.05 Angstrom (R = 0.168, 86 water molecules, two Mg2+ ca tions) are now presented. Helical parameters, stacking effects, the ge ometry at the duplex-tripler junction, and the hydration of the minor groove are discussed and compared with related theoretical and crystal structures.