FLP RECOMBINASE ESTROGEN-RECEPTOR FUSION PROTEINS REQUIRE THE RECEPTOR-D DOMAIN FOR RESPONSIVENESS TO ANTAGONISTS, BUT NOT AGONISTS

The ligand-binding domains of steroid receptors convey ligand-dependen t regulation to certain proteins to which they are fused. Here we char acterize fusion proteins between a site-specific recombinase, FLP, and steroid receptor ligand-binding domains, These proteins convert ligan d binding into DNA recombination. Thus, ligand binding is directly cou pled to an enzyme activity that is easily measured by DNA rearrangemen ts or heritable genetic changes in marker gene expression, as opposed to the multiple events leading to transcription, Recombination by a FL P-estrogen receptor (FLP-EBD) fusion is activated by all tested estrog ens, whether agonists or antagonists, indicating that all induce EBD r elease from the 90-kDa heat shock protein complex. Altering the distan ce between FLP and the EBD domain in the fusion proteins, by reducing the included length of the estrogen receptor D domain, affects ligand efficacy, A FLP-EBD with no D domain shows reduced inducibility by ago nists and, unexpectedly, complete insensitivity to induction by all an tagonists tested, A FLP-EBD including some D domain shows a ligand-ind ucible phenotype intermediate to those displayed by FLP-EBDs containin g all or none of the D domain, Thus, we observed a tethered interferen ce between FLP and the EBD domains that differs depending on the dista nce between the two domains, the conformations induced by agonists or antagonists, and which presents a previously undetectable distinction between estrogen agonists and antagonists in yeast.