A thermally driven interconversion of B and Z-dna.

CD and IR studies show that poly(dG-dMeC) in dilute Mg++ and Na+ solutions (e.g., 2 mM Mg++ and 55 mM Na+) undergoes reversible thermal interconversion of B and Z forms, in contrast to previous reports that the transition is independent of temperature and has an enthalpy change of zero. The B conformation is stable under the above conditions at lower temperature (approximately 5 degrees) and the Z form above approximately 20 degrees. The conversion is relatively slow in both directions, but is more rapid in the Z leads to B direction.