Structure and stability of Z* DNA

Area of Science:

• Molecular Biology
• Biophysics
• Structural Biology

Background:

• DNA can adopt various secondary structures beyond the canonical B-DNA form.
• Left-handed DNA structures, such as Z-DNA, have distinct structural and functional properties.
• Understanding DNA aggregation is crucial for comprehending its biological roles and potential applications.

Purpose of the Study:

• To investigate the structure and stability of the left-handed Z* DNA aggregate.
• To characterize the formation and dissolution mechanisms of Z* DNA.
• To explore the interaction of ethidium bromide with the Z* DNA aggregate.

Main Methods:

• Spectroscopic methods (circular dichroism, turbidity measurements).
• Electron microscopy for structural visualization.
• Kinetic and equilibrium binding studies.

Main Results:

• Poly(dGdC) forms a large, fibrous Z* DNA aggregate (approx. 20 nm diameter) in the presence of Mn++ and heat.
• Turbidity changes monitor Z* DNA formation, consistent with a nucleated condensation mechanism.
• Poly(dGm5dC) also forms Z* DNA, but other DNA types do not under tested conditions.
• Ethidium bromide induces Z* DNA dissolution and allosteric conversion to an intercalated, right-handed form.

Conclusions:

• Z* DNA represents a stable, aggregated left-handed DNA structure formed under specific conditions.
• The formation and dissolution of Z* DNA are dynamic processes influenced by ions and intercalating agents.
• Ethidium bromide's interaction with Z* DNA provides insights into DNA structural transitions and drug-DNA interactions.