DIFFERENTIAL-EFFECTS OF SPERMINE AND ITS ANALOGS ON THE STRUCTURES OF POLYNUCLEOTIDES COMPLEXED WITH ETHIDIUM-BROMIDE

The interactions of spermine and polyamine analogues with synthetic polynucleotides of various base sequences complexed with ethidium bromide (EB) were investigated using measurements of fluorescence intensity and steady-state fluorescence polarization. Spermine and polyamine analogues displaced some but not all of the EB bound to poly(dA-dT) . poly(dA-dT) or poly(dG-dC) . poly(dG-dC), suggesting that polyamines may stabilize these polynucleotides in a conformation with reduced affinity for EB. Modifications of the aliphatic backbone of spermine have pronounced effects on its ability to displace EB from poly(dA-dT) . poly(dA-dT) but not from poly(dG-dC) . poly(dG-dC). Spermine and some but not all of the polyamine analogues caused fluorescence depolarization when they interacted with the complex of EB and poly(dA-dT) . poly(dA-dT). Neither spermine nor any of the analogues, however, induced fluorescence depolarization in the complex of EB with poly(dG-dC) . poly(dG-dC) or poly(dA) . poly(dT). This suggests that spermine and some spermine analogues induce structural changes specific to alternating A-T sequences.