Interaction of androgen and glucocorticoid receptor DNA-binding domains with their response elements

Fusion proteins containing the glucocorticoid and the androgen receptor DNA-binding domain (ARF1 and GRF1) were produced in Escherichia coli. DNAse I footprinting was used to compare the interaction of these proteins with responsive elements (REs) in a typically glucocorticoid-responsive gene (mouse mammary tumour virus (MMTV)) and in an androgen-responsive gene (the C3(1) gene of rat prostatic binding protein). It is demonstrated that response elements which most closely resemble the consensus sequence show identical footprinting patterns for ARF1 and GRF1. The protected regions suggest that these sequences are occupied by two DNA-binding domains (DBDs) forming a dimer. Regions that constitute imperfect RE sequences, however, are apparently recognized by only one DBD, which mainly protects the TGTTCT motif. At these REs, the protection patterns produced by ARF1 and GRF1 are not identical. In the long terminal repeat (LTR) of MMTV but not in C3(1), a mechanism other than classical dimer formation seems to increase the affinity of ARF1 and GFR1 for these imperfect REs.