Epithelial and hemopoietic transmembrane mucin that may play a role in cell signaling. Homodimer of beta subunits. Also exists as a soluble form. Cleaved into two subunits, alpha and beta, probably between the first EGF domain and the SEA domain. Beta subunit contains the cytoplasmic tail and alpha subunit the extracellular tail. The homooligomerization into dimers is dependent on intrachain disulfide bonds (By similarity). Highly glycosylated.