The mammalian nuclear phosphoprotein DEK is implicated in multiple cellular processes, including transcriptional regulation, mRNA processing, and chromatin remodeling, and is associated with a number of clinical autoimmune and neoplastic conditions. DEK, an abundant chromatin-associated protein, changes the topology of DNA in chromatin in vitro. Although first identified in a fusion with the CAN/Nup214 nucleoporin protein in a specific subtype of acute myelogenous leukemia, DEK is also an autoantigen in patients with Pauciarticular onset juvenile rheumatoid arthritis. Furthermore, the last 65 amino acids of DEK can partially reverse the mutation-prone phenotype of cells from patients with ataxia-telangiectasia. The human DEK gene maps to chromosome 6p22.3.