Here is a picture of the estrogen receptor(ER) DNA-binding domain(ERDBD) bound to DNA. The ER is a nuclear hormone receptor, which are members of a superfamily of ligand-activated DNA-binding tranxcription factors. These will bind to DNA, and allow for the transcription machinery of the cells to begin transcription. When found inactive in the nucleus, ER is a monomer, but when bound by estrogen, it homodimerizes, and becomes active. A molecule of estrogen can be seen on the right. When this occurs, ER searches for its palindromic binding site, which consists of two 6 base pair consensus half sites seperated by three base pairs, known as the Estrogen Response Element or ERE. The binding site is held in place by a zinc-finger, which is just one of the many types of DNA-binding motifs.