BINDING OF TO-PRO-3 AND TOTO-3 TO DNA - FLUORESCENCE AND HOLE-BURNINGSTUDIES

The thiazole orange derivative, TO-PRO-3, and its dimeric analogue, TO TO-3, bind strongly to both double- and single-stranded DNA. Both the bound and the free dye undergo efficient nonphotochemical hole burning . From the structure of the hole burned and the fluorescence line-narr owed spectra, it is concluded that there are multiple modes of binding of the dyes to DNA. burned vibronic band structure are similar to tho se of the free dye. It is proposed that the molecules in this mode are externally bound to the DNA chain. Molecules in the other binding mod e are characterized by a strong interaction with DNA. These are propos ed to be molecules in intercalated or base-stacked configurations.