Effects of variations in length of hammerhead ribozyme antisense arms upon the cleavage of longer RNA substrates

The efficacy of intracellular binding of hammerhead ribozyme to its cleavage site in target RNA is a major requirement for its use as a therapeutic agent. Such efficacy can be influenced by several factors, such as the length of the ribozyme antisense arms and mRNA secondary structures. Analysis of various IL-2 hammerhead ribozymes having different antisense arms but directed to the same site predicts that the hammerhead ribozyme target site is present within a double-stranded region that is flanked by single-stranded loops. Extension of the low cleaving hammerhead ribozyme antisense arms by nucleotides that base pair with the single-stranded regions facilitated the hammerhead ribozyme binding to longer RNA substrates (e.g. mRNA). In addition, a correlation between the in vitro and intracellular results was also found. Thus, the present study would facilitate the design of hammerhead ribozymes directed against higher order structured sites. Further, it emphasises the importance of detailed structural investigations of hammerhead ribozyme full-length target RNAs.