Packing features of the all-AT oligonucleotide d(AAATTT).

Area of Science:

• Structural Biology
• Crystallography
• Molecular Biology

Background:

• Limited data exists for DNA sequences composed solely of adenine (A) and thymine (T) bases.
• Understanding DNA packing is crucial for comprehending genetic material organization and function.

Purpose of the Study:

• To elucidate the packing features of the oligonucleotide duplex d(AAATTT)2.
• To investigate the structural implications of adenine-thymine rich sequences in DNA.

Main Methods:

• X-ray diffraction was employed to determine the three-dimensional structure of the d(AAATTT)2 duplex.
• Analysis of base stacking interactions and helical parameters was performed.

Main Results:

• The d(AAATTT)2 duplex adopts a B-conformation with standard Watson-Crick hydrogen bonding.
• A helical arrangement of stacked oligonucleotides was observed.
• The virtual TA base step exhibits a negative twist, which favorably influences base stacking.

Conclusions:

• A-T rich DNA sequences tend to form helical stacks in the B-conformation.
• The negative twist at TA steps contributes to improved base stacking, correlating with their known lower stability in B-form DNA.