Apoptosis is mediated by death domain containing adapter molecules and a caspase family of proteases. Certain serine/threonine protein kinases, such as ASK-1 and RIP, are mediators of apoptosis. A novel serine/threonine kinase that mediates apoptosis was recently identified and designated ZIP kinase . ZIP kinase contains an N-terminal kinase domain and a C-terminal leucine zipper structure and binds to ATF4 that is a member of ATF/CREB family. ZIP kinase has high sequence homology to DAP kinase (death-associated protein kinase), which is a mediator of apoptosis induced by gamma interferon. Overexpression of ZIP kinase induces apoptosis. ZIP and DAP kinases represent a novel kinase family, which mediates apoptosis through their catalytic activities. The messenger RNA was ubiquitously expressed in various tissues.