Specificity in the interaction of 4',6-diamidino-2-phenylindole with polynucleotides

The binding of a fluorescent dye, 4',6-diamidino-2-phenylindole (DAPI) to polynucleotides was investigated by UV absorption and fluorescence spectroscopy. The results show that there are two types of bindings. In a higher concentration of DAPI, where UV spectroscopy is a suitable means for detecting the binding, the association of DAPI is independent of base compositions and the types of sugar moiety in spite of the spectral difference between DNA and RNA complexes with DAPI. On the other hand in a lower concentration of DAPI, where only fluorescence is measured to detect the binding, the degree of association is dependent upon the sugar types as well as base compositions.