DAPI-pUC8 complex: a tool to investigate biological effects of nucleic acid-drug interaction.

A complex consisting of pUC8, a 1.8 Md plasmid, and 4'-6-diamidino-2-phenylindole, a DNA-binding agent, has been performed in vitro under different conditions of ionic strength, and used to transform competent cells. A strong interference with the plasmid-coded activities, related to the P/D ratio where at the DNA-drug complex was formed, was shown to occur. Since the compound does not inhibit the uptake process neither affects plasmid activity once dissociated at high ionic strength, it is likely to be acting from inside the cell while still in the form of a DNA-adduct. This system is proposed as a useful tool to investigate the effects on target genes of drugs endowed with DNA sequence specificity.