Dlk, also known as ZIP kinase, is a serine/threonine kinase that is tightly associated with nuclear structures. Under certain conditions, which require cytoplasmic localization, Dlk can induce apoptosis. In search for interaction partners that might serve as regulators or targets of this kinase we identified apoptosis antagonizing transcription factor (AATF), a nuclear phosphoprotein of 523 amino acids. The 1.8 kb mRNA seems to be ubiquitously expressed. AATF contains an extremely acidic domain and a putative leucine zipper characteristic of transcription factors. Indeed, a Gal4-BD-AATF fusion protein exhibited strong transactivation activity. Interestingly, AATF interfered with Dlk-induced apoptosis.