A method is described which allows the rapid analysis of the binding of practically any molecules to DNA or to protein-DNA complexes (termed nucleoacidic protein or NAP). The antibiotic streptomycin sulfate, a soluble aminoglycoside, is used to precipitate the DNA after the ligand binding. Comparison of different sources and commercial batches of the antibiotic is described. Optimal conditions for precipitating DNA or NAP and the application of this method to the binding of the chick oviduct progesterone receptor to soluble NAP are described. The streptomycin method can be used with DNA molecules whose size ranges from 750 base pairs to greater than 50000 base pairs. The method works with a DNA or NAP from a variety of sources, including synthetic homo- or heteropolymers. The precipitation of DNA or NAP by streptomycin occurs rapidly and has minimal effects on the steroid receptor complex or binding of the steroid receptor to DNA or NAP. The requirements and limitations of the method as well as the optimal conditions for binding of the progesterone receptor to DNA or NAP are described.
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