CHEMICALLY-MODIFIED HAMMERHEAD RIBOZYMES WITH IMPROVED CATALYTIC RATES

A site-specific chemical modification strategy has been employed to el ucidate structure-function relationships at the only phylogenetically nonconserved position within the core of the hammerhead ribozyme (N7). Four different base substitutions at position 7 resulted in increased catalytic rates. A pyridin-4-one base substitution increased the rate of the chemical step up to 12-fold. These results are the first examp les of chemical modifications within a catalytic RNA that enhance the rate of the chemical step. Four base substitutions resulted in decreas ed catalytic rates. The results do not correlate with proposed hydroge n bond interactions (Pley et al., 1994; Scott et al., 1995). This stud y demonstrates the utility of using unnatural nucleotide analogs-rathe r than mutagenesis with the four standard nucleotides alone-to elucida te structure-function relationships of small RNAs.