Nanomechanics of negatively supercoiled diaminopurine-substituted DNA

Abstract

Single molecule experiments have demonstrated a progressive transition from a B- to an L-form helix as DNA is gently stretched and progressively unwound. Since the particular sequence of a DNA segment influences both base stacking and hydrogen bonding, the conformational dynamics of B-to-L transitions should be tunable. To test this idea, DNA with diaminopurine (DAP) replacing adenine was synthesized to produce linear fragments with triply hydrogen-bonded DAP:T base pairs. Triple hydrogen bonding stiffened the DNA by 30% flexurally.