Selection of hammerhead ribozymes for optimum cleavage of interleukin 6 mRNA.

Four GUC triplets in the coding region of the MRNA of interleukin 6 (IL-6) were examined for their suitabilty to serve as a target for hammerhead ribozome-mediated cleavage. This selection procedure was performed with the intention to downregulate IL-6 production as a potential treatment of those diseases in which IL-6 overexpression is involved. Hammerhead ribozymes and their respective short synthetic substrates (19-mers) were synthesized for these four GUC triplets. Notwithstanding the identical catalytic core sequences, the difference in base composition of the helices involved in substrate binding caused substantial variation in cleavage activity. The cleavage reactions on the 1035 nucleotide IL-6 mRNA transcript revealed that two ribozymes were able to cleave this substrate, showing a decrease in catalytic efficiency to 1/30 and 1/300 of the short substrate. This study indicates that the GUC triplet located at nucleotide 510 of the mRNA of IL-6 is the best site for hammerhead ribozyme-mediated cleavage. We suggest that in future targeting of chemically modified hammerhead ribosomes for cleavage of IL-6 RNA should be directed at this location.