On the behavior of Hoechst 33258 in DNA-PEG mixtures

Most of the studies on the interaction of fluorescent dyes with DNA have been performed under conditions radically different from those occurring in situ. Among others, this includes diluteness of experimental solutions, their homogeneity, and presence of a large amount of free water. To a certain extent, some model systems can help to approach the biological conditions. Thus, since some features of liquid-crystalline-like packaging of DNA were found in a number of living systems, to shed light on the behavior of Hoechst 33258 in biological-like conditions, we performed a detailed study of its properties in DNA-PEG mixtures, and, in particular, in the dispersed mesophases formed via polymer and salt induced (psi-) condensation. Being in complex with DNA, Hoechst 33258 shows a high sensitivity to the changes in osmotic conditions - the addition of PEG leads to a release of the dye molecules. However, this effect nonlinearly depends on osmolality. Individually, neither PEG nor NaCl at the studied concentrations significantly affect its complex with nucleic acid. The effect is caused precisely by their synergistic action. In cases of the dispersed systems formation, significant fraction of Hoechst 33258 molecules is retained within the resulting particles and is protected even from further increase in osmolality. This is partly due to competition between the processes of the dye releasing and formation of the dispersed particles.