A thermally driven interconversion of B and Z-dna

Area of Science:

• Molecular Biology
• Biophysics
• Structural Biology

Background:

• The B and Z forms represent distinct helical conformations of DNA.
• Previous studies suggested the poly(dG-dMeC) transition between these forms was temperature-independent with zero enthalpy change.

Purpose of the Study:

• To investigate the thermal interconversion of B and Z forms in poly(dG-dMeC) under specific ionic conditions.
• To re-evaluate the temperature dependence and thermodynamic properties of the B-Z DNA transition.

Main Methods:

• Circular Dichroism (CD) spectroscopy was employed to monitor DNA conformation.
• Infrared (IR) spectroscopy was utilized to study molecular structure and transitions.
• Experiments were conducted in dilute magnesium (Mg++) and sodium (Na+) solutions.

Main Results:

• Poly(dG-dMeC) exhibits reversible thermal interconversion between B and Z forms in 2 mM Mg++ and 55 mM Na+ solutions.
• The B conformation is stable below approximately 5°C, while the Z form is stable above approximately 20°C.
• The transition kinetics are relatively slow in both directions, with a faster Z to B conversion rate.

Conclusions:

• The B-Z DNA transition in poly(dG-dMeC) is temperature-dependent, contradicting earlier findings.
• Ionic conditions significantly influence the thermal stability and interconversion of DNA conformations.
• This study provides new insights into the dynamic structural behavior of DNA under physiological-like conditions.