Fluorescent labeling of DNA in solution with covalently bound acriflavin

We have prepared a fluorescent derivative of DNA based on the acriflavin-Feulgen histological procedure for staining DNA. Our procedure involved binding acriflavin to DNA in solution by reacting the acriflavin with aldehydes formed on the deoxyribose of DNA by controlled removal of a few percent of the purine bases of the DNA. Partially depurinated DNA was reacted with the acriflavin reagent, and unbound acriflavin was removed by chromatography on Sephadex G-25 eluted with phosphate buffered guanidine -HCl. Such single-stranded depurinated DNA bound 0.36 acriflavin molecules per 100 purine bases per h of depurination. DNA containing one bound acriflavin per 200 bases reassociated at 85% of the value of control DNA. The acriflavin - DNA complex showed new absorption maxima at 466 and 370 nm. The fluorescent product had excitation maxima at 304 and 465 nm and an emission maximum at 502 nm. This labeling procedure should be useful in place of or in addition to radioactive labeling for DNA.