Structure of a DNA duplex with all-AT base pairs

Area of Science:

• Structural biology
• Crystallography
• Molecular biology

Background:

• Oligonucleotide structures are crucial for understanding DNA function.
• Previous crystal structures have not shown this type of DNA duplex organization.

Purpose of the Study:

• To determine the crystal structure of the oligonucleotide duplex d(AAATATTT)(2).
• To elucidate the novel helical arrangement and packing of DNA duplexes in crystals.

Main Methods:

• X-ray crystallography was used to obtain two crystal forms of the d(AAATATTT)(2) duplex.
• Analysis of the crystal structures revealed Watson-Crick base pairing and helical stacking.

Main Results:

• Two crystal forms (form I and form II) of the d(AAATATTT)(2) duplex were identified.
• The duplexes formed helical columns with 11 or 14 duplexes per helix, exhibiting a pseudohexagonal arrangement.
• Lateral interactions were indirect, mediated by hydrated ions, resembling DNA fiber structures.

Conclusions:

• A previously undescribed organization of DNA duplexes in oligonucleotide crystals was discovered.
• The findings provide new models for DNA packing and interactions in crystalline states.
• The structural parameters are consistent with DNA structures containing CG terminal base pairs.