NUCLEIC-ACID SPIN-LABELING STUDY OF INTERACTION BETWEEN POLYADENYLIC-ACID - POLYURIDILIC ACID DUPLEX AND EGG PHOSPHATIDYLCHOLINE VESICLES -INVOLVEMENT OF TERMINAL AND INTERNAL NUCLEOTIDES AND SUGAR-PHOSPHATE BACKBONE

Model DNA-membrane contacts were studied in the system containing poly adenylic acid (polyA): polyuridilic acid (polyU) duplex and egg phosph atidylcholine (PC) vesicles without or in the presence of MgCl2. PolyU containing O-(1-oxyl-2,2,5,5-tetramethylpyrroline-3-carbonyl) spin la bel at 2'-OH moiety was used for spin labeling study of nucleic acid - phospholipid interactions. For polyA labeled with the same nitroxyl r adical EPR spectra from spin labels attached at terminal and at intern al nucleotide units contribute into the EPR spectrum of d.s. polynucle otide without or in the presence of egg PC vesicles and Mg ions. Inter nal spin labels are more sensitive to the interaction with PC-MLV than terminal ones. The complexation between s.s. polynucleotide and PC-ML V was shown. The values of spin labels' melting temperature of polyA : SL-polyU duplex at 1 mM MgCl2 reflect the changes in rotational mobil ity of terminal spin labels connected with duplex --> triplex transiti on. Arrhenius plots of temperature dependence of EPR spectra parameter s prove that ribose moieties of sugar-phosphate backbone are involved into the interaction between polynucleotide duplex and phospholipid bi layer. Egg PC vesicles demonstrate stabilizing effect on polyA : polyU duplex at 1 mM of Mg2+ and destabilizing effect at 5 mM Mg2+.