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

The interactions of spermine and polyamine analogues with synthetic po lynucleotides of various base sequences complexed with ethidium bromid e (EB) were investigated using measurements of fluorescence intensity and steady-state fluorescence polarization. Spermine and polyamine ana logues displaced some but not all of the EB bound to poly(dA-dT) . pol y(dA-dT) or poly(dG-dC) . poly(dG-dC), suggesting that polyamines may stabilize these polynucleotides in a conformation with reduced affinit y for EB. Modifications of the aliphatic backbone of spermine have pro nounced 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 n ot all of the polyamine analogues caused fluorescence depolarization w hen they interacted with the complex of EB and poly(dA-dT) . poly(dA-d T). Neither spermine nor any of the analogues, however, induced fluore scence depolarization in the complex of EB with poly(dG-dC) . poly(dG- dC) or poly(dA) . poly(dT). This suggests that spermine and some sperm ine analogues induce structural changes specific to alternating A-T se quences.