Alternative estrogen-dependent transcriptional regulation by ERα –ERβ homo- and heterodimers. The different modes of direct DNA binding of ER subtypes either as homo- or heterodimers to estrogen response elements (EREs) (A). Representation of the transcriptional regulation by ER subtypes through tethering to other transcription factors, such as activating protein 1 (AP-1) and stimulating protein 1 (Sp1) (B). The relative estrogen-dependent transcriptional activities are represented by the magnitude of the arrow. ERα and ERβ are represented in blue and white, respectively.