Crystal structure of d(CCGGGGTACCCCGG)2 at 1.4 Å resolution.

The X-ray crystal structure of the DNA tetradecamer sequence d(CCGGGGTACCCCGG)2 is reported at 1.4 Å resolution in the tetragonal space group P41212. The sequence was designed to fold as a four-way junction. However, it forms an A-type double helix in the presence of barium chloride. The metal ion could not be identified in the electron-density map. The crystallographic asymmetric unit consists of one A-type double helix with 12 base pairs per turn, in contrast to 11 base pairs per turn for canonical A-DNA. A large number of solvent molecules have been identified in both the grooves of the duplex and around the backbone phosphate groups.