Recombination-like structure of d(CCGCGG)

Area of Science:

• Structural Biology
• Crystallography
• Molecular Biology

Background:

• DNA can adopt various secondary structures beyond the canonical B-DNA form.
• Z-DNA is a left-handed helical structure characterized by alternating purine-pyrimidine sequences.
• Understanding DNA structural transitions is crucial for comprehending genetic processes.

Purpose of the Study:

• To determine the high-resolution crystal structure of the synthetic DNA hexamer d(CCGCGG).
• To investigate the structural basis of Z-DNA formation and intermolecular interactions.
• To explore potential models for DNA recombination and B/Z DNA junctions.

Main Methods:

• Single crystal X-ray diffraction analysis.
• Molecular replacement and refinement using molecular dynamics simulated annealing.
• Analysis of crystallographic data to 1.92 Å resolution.

Main Results:

• The structure revealed a Z-DNA duplex formed by the central alternating tetramer of d(CCGCGG).
• Intermolecular Watson-Crick base-pairing occurred between terminal nucleotides of symmetry-related molecules, forming a DNA twin.
• A sodium ion stabilized the twin structure, which exhibited recombination-like features and modeled B/Z junctions.

Conclusions:

• The crystal structure of d(CCGCGG) provides a detailed atomic model of Z-DNA formation.
• The observed intermolecular interactions and twin formation offer insights into DNA structural plasticity.
• This structure serves as a valuable model for understanding DNA junctions and recombination mechanisms.