Divalent hammerhead ribozyme targeting template region of human telomerase RNA has potent cleavage activity, but less inhibitory activity on telomerase.

The template region of human telomerase RNA is a crucial area for regulating telomerase activity and would be a good target for ribozymes. In fact, potent telomerase inhibitory activity of the ribozyme targeting the GUC sequence of the 5(') end of this region (36-ribosome) has been well demonstrated. To search for a more potent ribozyme, we designed a divalent ribozyme to cleave both the phosphodiester bonds following the GUC and the 23 nucleotides downstream of GUA. An in vitro cleavage study showed that this divalent ribozyme cleaved telomerase RNA more efficiently than the 36-ribozyme or the 59-ribozyme to target the GUA. When this ribozyme was introduced into the carcinoma cells, its inhibitory effect on telomerase activity was less than that of the 36-ribozyme. The 59-ribozyme showed minimum activity on telomerase. This implies that, although the divalent ribozyme possesses a potent cleavage activity on hTR in vitro, the 36-ribozyme is most potent to suppress telomerase activity.