Constructing an efficient trans-acting genomic HDV ribozyme.

We have engineered a genomic HDV ribozyme to construct several trans-acting ribozymes for use in trans to cleave target RNAs. Among the 10 different combinations attempted, only HDV88-Trans had cleavage activity on the 13-nucleotide substrate, R13, in vitro. To improve the cleavage efficiency, at least in vitro, of the HDV88-Trans ribozyme (kclv = 0.022 min(-1)), we have constructed several variants that differ in forming stem II (length) in the pseudoknot secondary structure model. When cleavage rate constants were analyzed and compared among variants of HDV88-Trans, HDV88-Trans-4 yielded kclv = 1.7 min(-1). HDV88-Trans-4 thus represents the highest active genomic HDV ribozyme that functions in trans thus far constructed, and has activity under physiological conditions (pH 7.1 at 37 degrees C with 1 mM of MgCl2).