Transport of intracellularly active ribozymes to the cytoplasm

Ribozymes are RNA molecules with enzymatic activity which selectively bind and cleave specific target RNAs. To date, numerous studies directed toward the application of ribozymes in vivo have been performed and many successful experiments have been reported. However, to induce high-level activities of ribozymes in vivo, several factors must be considered. Here we report that the cytoplasmic localization of ribozymes is important for their intracellular activity in mammalian cells. Northern blot analysis revealed that a tRNA(Val) ribozyme, which can assume a cloverleaf structure similar to that of a native tRNA, is efficiently transported to the cytoplasm. In contrast, the tRNAiMet-driven ribozyme, which does not maintain the cloverleaf structure, remained predominantly in the nucleus. In correlation with the localization, the activity of the exported ribozyme was higher than that of the ribozyme retained in the nucleus. These results should provide insight into the design of ribozymes that have high-level activity in mammalian cells.