FIG. 1.

ERα and ERβ form heterodimer complexes in vivo. 293T cells were transiently transfected with ER expression vectors as indicated for 24 h, and whole-cell extracts were prepared. A 10-μg sample of each extract was subjected to EMSA in the presence of 50,000 cpm of ³²P-labeled ERE. The presence of each receptor in the heterodimeric complexes was identified by incubating the binding reaction mixtures in the presence of ERα- or ERβ-specific antibodies (αAb and βAb), leading to supershifted complexes (SC). Entire binding reaction products were loaded onto a 5% polyacrylamide gel and electrophoresed for 2 to 3 h at 150 V. Dried gels were exposed overnight at −85°C. The positions of the homo- and heterodimeric complexes (α, β, and α/β) are indicated.