Highly purified. An 18aa peptide unique to the rat ERb2. Peptide is unique to rat ERb2 and its variant ERb2d3. Mouse/rat ERb1 gene encodes a protein of 485aa with a calculated size of approx. 54kD (1). Rat ERb1 is highly conserved in the DNA-binding domain (>90% homology) and the C-terminal ligand binding domain (55% homology). The A/B domain, the hinge region and the F-domain are not conserved. Rat ERb1 is primarily expressed in prostate, ovary, lung, bladder, brain, uterus, and testis. Most recently functional variants of ERb1, termed ERb2, have been cloned. ERbb has an additional 18 aa as a results of in-frame mutation within the ligand-binding domain. ERb1 is expressed in ovary, prostate, pituitary, brain, and muscle. Variants of both ERb1 and ERb2 (ERb1d3, ERb2d3) were detected that show deletion of 39 aa in the DNA-binding domain. Both ERb1 and ERb2 specifically bind to ER response element. ERa, b1 and ERb2 have been found to heterodimerize with each other.