Estrogen receptor positive

estrogen receptor 1 (ER-alpha)
A dimer of the ligand-binding region of ERα (PDB rendering based on 3erd​).
Identifiers
Symbol	ESR1
Alt. symbols	ER-α, NR3A1
Entrez	2099
HUGO	3467
OMIM	133430
PDB	1ERE
RefSeq	NM_000125
UniProt	P03372
Other data
Locus	Chr. 6 q24-q27

estrogen receptor 2 (ER-beta)
A dimer of the ligand-binding region of ERβ (PDB rendering based on 1u3s​).
Identifiers
Symbol	ESR2
Alt. symbols	ER-β, NR3A2
Entrez	2100
HUGO	3468
OMIM	601663
PDB	1QKM
RefSeq	NM_001040275
UniProt	Q92731
Other data
Locus	Chr. 14 q21-q22

Estrogen receptors (ERs) are a group of proteins found inside and on cells. They are receptors that are activated by the hormone estrogen (17β-estradiol). Two classes of ER exist: nuclear estrogen receptors (ERα and ERβ), which are members of the nuclear receptor family of intracellular receptors, and membrane estrogen receptors (mERs) (GPER (GPR30), ER-X, and G_q-mER), which are mostly G protein-coupled receptors. This article refers to the former (ER).

Once activated by estrogen, the ER is able to translocate into the nucleus and bind to DNA to regulate the activity of different genes (i.e. it is a DNA-binding transcription factor). However, it also has additional functions independent of DNA binding.

As hormone receptors for sex steroids (steroid hormone receptors), ERs, androgen receptors (ARs), and progesterone receptors (PRs) are important in sexual maturation and gestation.

There are two different forms of the estrogen receptor, usually referred to as α and β, each encoded by a separate gene (ESR1 and ESR2, respectively). Hormone-activated estrogen receptors form dimers, and, since the two forms are coexpressed in many cell types, the receptors may form ERα (αα) or ERβ (ββ) homodimers or ERαβ (αβ) heterodimers. Estrogen receptor alpha and beta show significant overall sequence homology, and both are composed of five domains designated A/B through F (listed from the N- to C-terminus; amino acid sequence numbers refer to human ER).