The domain organization of the full-length 595 amino acid ERα (67kDa), and truncated shorter isoforms (62kDa, 53kDa, 46kDa, 45kDa, and 36kDa) resulting from alternative splicing and/or alternate translation start sites are illustrated. Protein domains are labeled as A to F with numbering denoting amino acid sequence number based on the full-length protein (595 aa). ERα domains: N-terminal (NTD, A/B domains, AF-1), DNA binding domain (DBD, C domain), hinge (D) domain, and C-terminal region containing the ligand binding domain (LBD, E/F domain, AF-2).