RECEPTOR ACCESSORY FACTOR ENHANCES SPECIFIC DNA-BINDING OF ANDROGEN AND GLUCOCORTICOID RECEPTORS

Protein-protein interactions are common among transcriptional activato rs and may have important consequences for gene regulation. Using the mobility shift assay, we have identified a factor that enhances specif ic DNA binding of truncated rat androgen (AR) and glucocorticoid (GR) receptors by 25- and 6-fold, respectively, through the formation of he teromeric complexes. This factor, designated receptor accessory factor , or RAF, also potentiates DNA binding of full-length human GR. RAF is temperature and trypsin sensitive and is present in a variety of cult ured mammalian cells. By gel filtration RAF has a predicted molecular mass of 130 kDa. RAF enhancement of AR-DNA binding is optimal with and rogen response element DNA. RAF appears to interact directly with AR b ecause 1) deoxycholate, which interferes with protein-protein but not protein-DNA interactions, prevents RAF.AR.DNA complex formation, 2) RA F activity is recovered from an androgen response element DNA affinity column only in the presence of AR, and 3) RAF increases the size of a n AR.DNA complex by gel filtration. Mutagenesis of truncated AR fragme nts indicates that a region in the NH2-terminal domain is required for RAF to enhance AR-DNA binding. The interaction of RAF with AR and GR suggests that RAF might influence the ability of these nuclear recepto rs to activate transcription.