Reinterpretation of fluorescence of terbium ion-DNA complexes.

Terbium (Tb3+) fluorescence was used to investigate local non-denaturation perturbations of double-helical DNA structure induced in this nucleic acid by various physical and chemical agents. It has been shown that the interaction of Tb3+ with DNA into which single-strand or double-strand breaks have been introduced by DNase I or by low doses of ionizing radiation does not influence the fluorescence of the lanthanide cation. On the other hand, interaction of terbium with DNA modified by the antitumour drug cis-diamminedichloroplatinum(II) at low levels of binding and by low doses of ultraviolet radiation (wavelength 254 nm) has been shown to result in substantial enhancement of the fluorescence of this cation. It has been proposed that the terbium fluorescent probe can also be exploited successfully for the purpose of analysing the guanine bases present in distorted double-stranded regions of DNA, in which only the vertical stacking of the base-pairs is altered.