Comparison of X-ray crystal structures of a tetradecamer sequence d(CCCGGGTACCCGGG)2 at 1.7 Å resolution.

We presented a comparison of three different X-ray crystal structures of DNA tetradecamer sequence d(CCCGGGTACCCGGG)2 all at about 1.7 Å resolution. The sequence was designed as an attempt to form a DNA four-way junction with A-type helical arms. However, in the presence of magnesium, it does not take up the junction structure, but forms an A-type double helix in P41212 space group. This allowed us to study possible conformational changes in the double helix due to the presence of metal ions. Though the crystallization condition has magnesium chloride, it was not observed in the electron density map.