In accordance with the present invention, there are provided a gene encoding the promoter region of a protein p51 which is capable of inducing cell death, and a gene encoding the 5-untranslated region of p51. These genes are useful in diagnosing and treating diseases including cancer caused by abnormal regulation of cell propagation. Furthermore, in accordance with the present invention, there are provided the antisense DNAs and the antisense RNAs of these genes, nucleic acid probes comprising parts or all of these genes, methods of detecting the above genes of the present invention or analogous genes using the nucleic acid probes, transformants in which the above gene of the present invention has been introduced, and methods of screening drugs using them. These genes are also useful in diagnosing and treating diseases including cancer, etc.