Cells are continuously exposed to environmental stresses and respond to them to maintain cellular homeostasis. Failure to respond to these stresses may cause pathological states such as renal failure, complications of diabetes, and autoimmune diseases. Signal transduction induced by osmotic and cold stresses is not fully understood. In addition, mechanisms of these stress responses are yet to be elucidated. Activation of many signaling pathways induces translocation of proteins into the nucleus to transduce signals and regulate nuclear functions. By using inducible translocation trap (ITT), a reporter gene–based screening technique, nuclear translocation of 2-amino-3-ketobutyrate coenzyme A ligase (KBL) was detected in response to cold and osmotic stresses. Rapid nuclear translocation of KBL was confirmed by biochemical analysis and fluorescent microscopy. A large region of KBL was required for stress-induced nuclear translocation. The KBL reporter system will be a useful tool for the investigation of cold and osmotic stress responses.