PTAG is a novel 386 amino acid multi-pass membrane protein that contains one UBA domain and augments drug-induced apoptosis. Cells lacking PTAG have a reduced apoptotic response, thereby causing a predisposition to cell malignancy and resistance to chemotherapeutic interventions, and PTAG plays a role in colorectal tumorigenesis as the majority of primary colorectal tumors lack the PTAG gene. Encoded by a gene located on human chromosome 22, PTAG is often co-expressed with EWS (ewing sarcoma breakpoint region 1), a gene located directly downstream of PTAG.