Kenneth G. Draper

Chemical modification of hammerhead ribozymes. Catalytic activity and nuclease resistance.

A systematic study of selectively modified, 36-mer hammerhead ribozymes has resulted in the identification of a generic, catalytically active and nuclease stable ribozyme motif containing 5 ribose residues, 29-30 2′-O-Me nucleotides, 1-2 other 2′-modified nucleotides at positions U4 and U7, and a 3′-3′-linked nucleotide “cap.” Eight 2′-modified uridine residues were introduced at positions U4 and/or U7. From the resulting set of ribozymes, several have almost wild-type catalytic activity and significantly improved stability. Specifically, ribozymes containing 2′-NH substitutions at U4 and U7, or 2′-C-allyl substitutions at U4, retain most of their catalytic activity when compared to the all-RNA parent. Their serum half-lives were 5-8 h in a variety of biological fluids, including human serum, while the all-RNA parent ribozyme exhibits a stability half-life of only 0.1 min. The addition of a 3′-3′-linked nucleotide “cap” (inverted T) did not affect catalysis but increased the serum half-lives of these two ribozymes to >260 h at nanomolar concentrations. This represents an overall increase in stability/activity of 53,000-80,000-fold compared to the all-RNA parent ribozyme.