Significantly higher activity of a cytoplasmic hammerhead ribozyme than a corresponding nuclear counterpart: engineered tRNAs with an extended 3 ' end can be exported efficiently and specifically to the cytoplasm in mammalian cells

Hammerhead ribozymes were expressed under the control of similar tRNA promo ters, localizing transcripts either in the cytoplasm or the nucleus, The tR NA(Val)-driven ribozyme (tRNA-Rz; tRNA with extra sequences at the 3 ' end) that has been used in our ribozyme studies was exported efficiently into t he cytoplasm and ribozyme activity was detected only in the cytoplasmic fra ction. Both ends of the transported tRNA-Rz were characterized comprehensiv ely and the results confirmed that tRNA-Rz had unprocessed 5 ' and 3 ' ends , Furthermore, it was also demonstrated that the activity of the exported r ibozyme was significantly higher than that of the ribozyme which remained i n the nucleus, We suggest that it is possible to engineer tRNA-Rz, which ca n be exported to the cytoplasm based on an understanding of secondary struc tures, and then tRNA-driven ribozymes may be co-localized with their target mRNAs in the cytoplasm of mammalian cells.