Study of applicability of the bifunctional system ethidium bromide plus hoechst-33258 for DNA analysis

Changes in absorbance and fluorescence excitation and emission spectra in the ultraviolet and visible regions of the system containing ethidium bromide (EtBr) and Hoechst-33258 (Ht) were investigated depending on various DNA quantities and the composition of the medium. It is noted that spectral properties of this system are determined by interactions of EtBr and Ht both with nucleic acid and with one another (for example, joint sorption of EtBr and Ht on DNA may involve fluorescent resonance energy transfer between the dye molecules). Thus, different modes of EtBr and Ht specificity to substrate and assay conditions suggest that combined use of these dyes provides some additional effects that may be interesting in terms of structure-functional study of nucleic acid. Some of these effects are considered in this paper.