The estrogen receptor-alpha (ER) is a broadly expressed transcription factor which controls a number of genes involved in cellular differentiation and proliferation. ER contains two transcriptionally active domains: the N-terminal domain (AF1) is constitutively active, while the C-terminal domain (AF-2) is hormone-dependent. ER is subject to post-translational modification, including phosphorylation of serine residues 104, 106, 118, and 167. This antibody specifically recognizes human estrogen 
receptor-alpha when phosphorylated at serine 167, a site which influences AF-1 dependent transcriptional activity. This phosphorylation is catalyzed by the MAPK pathway, potentially through the 90 kDa ribosomal S6 kinase (pp90rsk1). Serine 167 is also a consensus Akt substrate.