Interaction of Nucleic Acids, I. Physical Binding of Thymine, Adenine, Steroids, and Aromatic Hydrocarbons to Nucleic Acids
The interaction of steroids and polycyclic carcinogens with nucleic acids was investigated. Native and denatured DNA from calf thymus were deproteinized and precipitated. Yeast RNA, pea ribosomal RNA, and calf thymus histone were prepared. Equilibrium dialysis was performed using nucleic acid solution. Binding constants were measured. Tritiated thymine (65714), adenine, (73245), 17-beta-estradiol (50282), testosterone (58220), diethylstilbestrol (56531), phenanthrene (85018), and naphthalene (91203), and carbon-14 labeled caffeine (58082) were used to evaluate the binding of nucleic acids. Partition coefficients of the radiochemicals were measured. Radioactivity was measured by scintillation counting. All experiments were conducted at 5 degrees-C. The affinity of the compounds was generally greater for the coil form of nucleic acids than for the helix or native form. Denatured DNA had 200 percent greater affinity for the substrates than RNA. There was a correlation between partition coefficients and the number of binding sites and the binding constant. The order of increasing affinity constants of compounds to nucleic acids was thymine, adenine, caffeine, naphthalene, diethylstilbestrol, 17-beta-estradiol, testosterone, and phenanthrene.