Our previous findings suggest that the activation of the rat intronless myc gene provides a selective advantage in tumor suppression through apoptosis induction. In the present study, to examine whether intronless myc gene acting as an apoptosis inducer is evolutionarily conserved in mammalian cells, we isolated the mouse intronless myc gene and characterized it. A sequence analysis demonstrated that mouse intronless myc gene, ms-myc, has a linearly opened translatable frame consisting of 1293bp with 90% homology with that of rat s-myc. The chromosomal locus of ms-myc was identified on chromosome 19B by a fluorescent in situ hybridization (FISH) analysis. Gene transfection experiments showed that the transient overexpression of ms-Myc with transactivation activity effectively induces cell death in a wild-type p53-independent manner. In addition, cells stably expressing transfected ms-myc became more susceptible to apoptosis induced by genotoxic stress such as UV-irradiation and hydrogen peroxide compared with untransfected control cells. These observations suggest that the rodents commonly contain an s-myc-type of intronless myc gene with apoptosis-inducing activity.