The transcriptional activation function located in the hormone-binding domain of the human oestrogen receptor is not encoded in a single exon.

Using GAL4 chimeric receptors, we have reported previously that the hormone-binding domain (HBD) of the human oestrogen receptor (hER) contains an hormone-inducible transcription activation function. We have extended that study here to show that this activation function represents the major activating domain in the hER in HeLa cells. In addition, we have expressed the various exons encoding the hER HBD as GAL4 fusion proteins and have shown that none contain a discrete activation function. Thus the activating domain of the hER HBD appears to be different from the recently characterized 'simple' activating domains, such as acidic 'blob' or amphipathic helix, and more likely corresponds to a protein surface created from dispersed elements and dependent upon the three-dimensional folding of the HBD.