A HIGHLY CONSERVED REGION IN THE HORMONE-BINDING DOMAIN OF THE HUMAN ESTROGEN-RECEPTOR FUNCTIONS AS AN EFFICIENT TRANSACTIVATION DOMAIN IN YEAST

Human estrogen receptor (hER) mutants which activate transcription in the absence of hormone were isolated by random mutagenesis and genetic selection in the yeast Saccharomyces cerevisiae. Twenty constitutive hER mutants defining ten different alleles were selected. All sequence changes resulted in truncations of the receptor within a 123-amino-ac id (aa) segment (aa 270 to 393) spanning the D region and the N-termin al part of region E which contains the hormone-binding domain (HBD). T ransactivation assays using both the constitutive hER mutants and a se ries of deleted receptor derivatives generated in vitro revealed that the N-terminal part of region E, between aa 302 and 339, contains an e fficient transcriptional activation function which is constitutively a ctive in yeast. The location of this transactivation function in hER i s similar to that of the tau 2 activation function of the glucocortico id receptor and corresponds to a sequence which is highly conserved am ong the steroid hormone receptors. Thus, a conserved region exists in the HBD of the hER which can function as an autonomous transactivation domain.