Many leukemias result from chromosomal translocations that lead to the generation of chimeric oncoproteins. Chimeric gene for the promyelocytic leukemia-retinoic acid receptor alpha (PML-RAR alpha) is the hallmark of acute promyelocytic leukemia. Specific gene silencing of an oncogene is desirable for the treatment of these diseases. We have previously constructed an allosterically controllable ribozyme (designated maxizyme) targeted for bcr-abl chimeric mRNA, whose cleavage activity is induced only in the presence of a specific RNA sequence of interest. It has been demonstrated recently that RNA interference induced by short hairpin-type RNAs provides a powerful method for sequence-specific gene silencing. Here we report that DNA vector-based maxizymes and short hairpin-type RNAs driven by the promoter of a human gene for tRNA(Val) specifically inhibit the expression of the chimeric gene for PML-RAR alpha both in vitro and in vivo. Our findings confirm the potential utility of maxizymes and shRNAs as therapeutic agents.