Binding to Nucleic Acids?

ABSTRACT: The mechanism of the enhancement of the fluo-rescence of ethidium bromide on binding to double helical RNA and DNA has been investigated. From an examination of the effect of different solvents on the fluorescence lifetime, quenching of fluorescence by proton acceptors, and the sub-stantial lengthening of lifetime observed upon deuteration of the amino protons, regardless of the medium, we conclude that proton transfer from the excited singlet state is the process primarily responsible for the low fluorescence yield in most polar solvents. Enhancement of fluorescence upon intercalation E t h i d i u m bromide, a cationic dye (structure I) which in-teracts strongly and specifically with double helical RNAs and DNAs, is widely used in spectrofluorimetric studies because of the striking fluorescence enhancement it displays upo