Enhancement in the cleavage activity of a hammerhead ribozyme by cationic comb-type polymers and an RNA helicase in vitro.

The activity of a hammerhead ribozyme (Rz) in vivo depends on several factors, such as abundance, stability, and accessibility of Rz to its target mRNA. Among these factors, accessibility is believed to be the rate-limiting factor for Rz-mediated cleavage in vivo. As Rz and its substrate RNA are negatively charged, we examined whether cellular RNA-interacting proteins or artificial polycations might improve the accessibility of Rz to its substrate RNA. Specifically, we examined the effects of two kinds of cationic comb-type copolymer, alphaPLL-g-Dex, and a cellular RNA helicase on the accessibility of Rz to a model structured RNA in vitro. The cleavage activity of Rz was slightly enhanced by alphaPLL-g-Dex, probably due to an acceleration of the association/dissociation rate. And also, the RNA helicase-bound hybrid-Rz could cleave the target substrate at a significantly higher rate due to its unwinding activity for the duplex RNA substrate. These approaches should be useful in the development of efficient gene-inactivating reagents in the post-genomic era.