A fragment of the rat androgen receptor (amino acids 533-637) containing the DNA-binding domain was produced in Escherichia coli as a fusion product with protein A of Staphylococcus aureus. The fusion protein was purified on IgG-Sepharose, a method that does not involve the use of denaturing agents. Approximately 4 mg of fusion protein was obtained from 500 ml of bacterial culture. In gel shift assays, the recombinant DNA-binding domain displays an affinity for a fragment of the long terminal repeat of mouse mammary tumor virus and for an intronic fragment of the gene coding for the C3 component of the androgen-regulated rat prostatic binding protein. In a DNase I footprinting assay, the fusion protein protects a sequence in the C3 fragment that has previously been shown to act as a functional androgen response element. Interestingly, a single base pair mutation in the response element, which abolishes androgen inducibility, also destroys the ability to interact with the recombinant androgen receptor DNA-binding domain.