Molecular structure of nicked DNA: A substrate for DNA repair enzymes

The molecular structure of a nicked dodecamer DNA double helix, made of a ternary system containing d(CGCGAAAACGCG) + d(CGCGTT) + d(TTCGCG) oligonucleotides, has been determined by x-ray diffraction analysis at 3 Å resolution. The molecule adopts a B-DNA conformation, not unlike those found in intact dodecamer DNA molecules crystallized in a somewhat different crystal lattice, despite a gap due to the absence of a phosphate group in the molecule. The helix has a distinct narrow minor groove near the center of the molecule at the AAAA region. This suggests that the internal stabilizing forces due to base stacking and hydrogenbonding interactions are sufficient to overcome the loss of connectivity associated with the disruption of the covalent backbone of DNA.