Evaluation of five basic fluorochromes of potential use in microfluorometric studies of nucleic acids

Five basic fluorochromes were evaluated to determine whether or not any could be used in microfluorometric studies for the selective demonstration of nucleic acids. Only two of the fluorochromes - Nuclear Yellow (Hoechst 769121) and the phenoxyindole compound D261/37 - were found to be selective for nucleic acids, while the other three fluorochromes produced small to moderate amounts of fluorescence in preparations extracted sequentially with RNase and DNase. All of the fluorochromes could be considered "structural probes" since they produced less fluorescence in the highly condensed chromatin of thymocyte nuclei than they did in the less condensed chromatin of hepatocyte nuclei. When exposed to continuous excitation for 2-min intervals, hepatocyte nuclei stained with Nuclear Yellow or D261/37 gradually lost, respectively, approximately 21% or nearly 60% of their original fluorescence. Nuclei stained with the other three fluorochromes displayed much more rapid fading and lost more than 80% of their original fluorescence.