[Mechanism of AT base pairs recognition by molecules of dye "Hoechst 33258"]

Experimental studies are reported on the binding of the dye "Hoechst 33 258" to DNA and synthetic polynucleotides. A stereochemical model of binding of the dye to DNA is proposed. According to the model, the molecules of the dye are located in the minor groove of DNA, each covering 4 base pairs. The benzimidazole backbone of the dye tends to form a helix isogeometric to that of DNA in the B form. The specifisity of "Hoechst 33 258" binding to At pairs involves hydrogen bonding of two NH-groups of benzimidazole rings and CH3N+H group of the piperazine ring to O2 oxygenes of thymines and N3 nitrogens of adenines facing the minor groove of the DNA double helix.