The joint effect of Ethidium Bromide (EtBr) and Hoechst 33258 (H33258) on double-stranded DNA (ds-DNA) stabilization was investigated to understand the mechanisms of simultaneous interactions of these ligands with DNA. EtBr is a classic intercalator and binds with DNA with weak preference to GC-rich sequences of polynucleotide. At the same time H33258 is a minor groove binding ligand showing high preference for AT-sequences of polynucleotide. At joint interaction of EtBr and H33258 with double stranded DNA prevailing influence of one of them is revealed depending on the ligand concentration: at low concentrations effect of EtBr on the stabilization of ds-DNA is more distinct, when increase the concentration leads to the significant increase of the effect of H33258.

Detailed analyses of obtained experimental data show, that joint effect of two ligands having different types of binding to DNA on dynamic characteristics of helix-coil transition is not the simple sum of the separate effect of the ligands bound with DNA in accordance with the earlier developed theory (1).

References and Footnotes

1. Karapetian A. T., Vardevanian P. O., Terzikian G. A., Frank-Kamenetskii M. D. J.Biomol. Struct. & Dyn. 8, 123-130 (1990).