Generation and application of asymmetric hammerhead ribozymes

Most researchers who intend to suppress a particular gene are interested primarily in the application of ribozyme technology rather than its mechanistic details. This article provides some background information and describes a straightforward strategy to generate and test a special design of a ribozyme: the asymmetric hammerhead ribozyme. This version of a hammerhead ribozyme carries at its 5' end the catalytic domain and at its 3' end a relatively long antisense flank that is complementary to the target RNA. Asymmetric hammerhead ribozymes can be constructed via polymerase chain reaction amplification, and rules are provided on how to select the DNA oligonucleotides required for this reaction. In addition to details on construction, we describe how to test asymmetric hammerhead ribozymes for association with the target RNA in vitro, so that RNA constructs can be selected and optimized for fast hybridization with their target RNA. This test can allow one to minimize association problems caused by the secondary structure of the target RNA. Additionally, we describe the in vitro cleavage assay and the determination of the cleavage rate constant. Testing for efficient cleavage is also a prerequisite for reliable and successful application of the technology. A carefully selected RNA will be more promising when eventually used for target suppression in living cells.