A model for the sequence-dependent DNA binding of 4',6-diamidino-2-phenylindole (DAPI).

A study on the sequence dependent DNA binding mode of DAPI has been carried out on pUC8 and the beta gal promoter region by restriction endonuclease and DNAase I protection experiments. A molecular model depicting drug interaction at the level of selected palyndromes has also been constructed that confirms the A-T sequence specificity of the compound. Experimental data indicate that the binding sites for RNA polymerase and cyclic AMP receptor protein (CRP) in the beta gal gene are privileged locales for DAPI interaction, a feature that explains impairment of transcription at this level. From a stereochemical view point, DAPI binding to DNA minor groove, while being incompatible with promoter unwinding in the open complex, may also disturb optimal contacts with proteins regulating RNA polymerase activity.