THE EFFECTS OF CU2- DNA CONDENSATION AND DENATURATION STUDIED BY FOURIER-TRANSFORM IR DIFFERENCE SPECTROSCOPY( AND PB2+ ON THE SOLUTION STRUCTURE OF CALF THYMUS DNA )

The interaction of calf thymus DNA with CU2+ and Pb2+ was studied in a queous solution at pH 6.5 with metal/DNA(P) (P = phosphate) molar rati os (r) 1/80, 1/40, 1/20, 1/10, 1/4, 1/2, and 1, using Fourier Transfor m ir (FTIR) spectroscopy. Correlations between the ir spectral changes , metal ion binding mode, DNA condensation, and denaturation, as well as conformational features, were established. Spectroscopic evidence h as shown that at low metal/DNA(P) molar ratios 1/80 and 1/40, copper a nd lead ions bind mainly to the PO2- of the backbone, resulting in inc reased base-stacking interaction and duplex stability. The major coppe r ion base binding via G-C base pairs begins at r > 1/40, while the le ad ion base binding occurs at r > 1/20 with the A-T base pairs. The de naturation of DNA begins at r = 1/10 and continues up to r = 1/2 in th e presence of copper ions, whereas a partial destabilization of the he lical structure was observed for the lead ion at high metal ion concen tration (r = 1/2). Metal-DNA binding also results in DNA condensation. No major departure from the B-family structure was observed, upon DNA interaction with these metal ions. (C) 1993 John Wiley and Sons, Inc.