Binding of small organic molecules to a model nucleoprotein

The importance of DNA-protein-small molecule interactions in the control of genetic expression is now clearly established. Spectrophotometric and fluorometric titration of acridine orange, 9-aminoacridine, and ethidium bromide with DNA and a model nucleoprotein, composed of DNA complexed with poly-L-lysine, indicate that these small molecules successfully compete with poly-L-lysine for binding sites on DNA. A comparison of the absorption spectra of l-hydroxyacridine and l-hydroxyanthracene in the presence of DNA gives some insight into the nature of acridine-DNA interaction under the conditions of our experiments. Also described are preliminary efforts toward the extension of existing techniques to the study of carcinogenic hydrocarbons in this context. The possible significance in nature of small molecule-protein competition for DNA binding sites is discussed.