Identification of a high molecular weight steroid response element binding protein

In this study we report the identification of a Steroid Response Element-Binding Protein (SRE-BP) present in whole cell extracts of HeLa cells and GH3 pituitary tumor cells which specifically binds to two classes of functionally distinct SREs. In gel retardation experiments SRE-BP binds preferably to oligonucleotides containing an estrogen response element (ERE) or a symmetrical glucocorticoid response element (GRE); it binds less well to a mutant GRE and poorly, if at all, to a thyroid response element (TRE). The SRE-BP does not recognize transcription factor binding sites present in the promoter of the Herpes Simplex Virus thymidine kinase gene. We have shown, using gel filtration chromatography that the SRE-BP has a relative molecular weight under nondenaturing conditions of 205 K (+/- 20 K). The SRE-BP is not a steroid receptor as evidenced by different DNA sequence specificity, cell type distribution, and molecular weight. We propose that by modulating the interaction of steroid receptors with target SREs, the SRE-BP plays a role in specificity of steroid hormone action.