Fig. 1. Physical and transcriptional interrelationships between hERα and COUP-TFI. (A) Schematic illustration of the hERα sequence: domains and associated functions. (B) Transfection experiments in CHO-K1 cells were performed using the 0.2 basic, ERE-TK or chicken vitellogenin (Vg) reporters, pCH110 internal control and 25 ng of each expression vector (pCMV5/hERα and pCDNA/COUP-TFI). Cells were treated with ethanol (EtOH) or 10^–8 M estradiol (E2). Values are shown as the fold induction of normalized luciferase reporter activity (mean ± SEM). (C) Co-immunoprecipitation of the endogenous hERα–COUP-TFI complex in MCF-7 cells using anti-COUP-TFI- specific antibody. A goat pre-immune serum (PreI) was the control. The presence of each component of the complex was checked by western blots. (D) GST pull-down experiments performed using 250 ng of the GST–COUP-TFI 57–423 fusion protein or GST as a control, with in vitro labeled hERα. Input is 40% of the labeled protein used in the assay.