Abstract: The effect of metal ions of different valences on the conformation of DNA molecules by UV spectra has been studied. The result shows that a hypochromicity occurs at 257 nm after adding metal ions, and the degree of hypochromicity depends on the valence of metal ions. The higher the valence of metal ion, the stronger the hypochromicity. It follows that interactions of metal ions with DNA molecules cause contraction of DNA conformation. The higher the valence of the metal ion, the stronger the effect, eventually, DNA condensation may be induced. The phenomena has been disscussed according to Modern Polyelectrolyte Theory, and the result is satisfactory.

Key words: Conformation, Hypochromicity, Condensation, Flexibility, UV spectra