CDCP1 is a novel, 135kD cell surface glycoprotein that is found on tumor, stem cells, keratinocytes and colonic epithelial cells. It is reported that this protein is overexpressed in colon and lung cancers. It is a type I transmembrane (TM) protein that is involved with cell adhesion. Mouse CDCP1 is synthesized as an 833 amino acid (aa) precursor. It contains an extracellular region with three CUB domains (aa30-667) and a phosphotyrosine site at Tyr731. When unligated, CDCP1 can be proteolytically cleaved between aa’s 270-300. This generates an 80kD TM protein that may be missing the N-terminal CUB domain (aa221-350). Over aa’s 25-667, mouse CDCP1 is 83% and 92% aa identical to human and rat CDCP1, respectively.