RNAi - Strategy to Control Viral Infections in Eukaryotic Organisms

Short double-stranded RNA molecules efficiently inhibit gene expression in eukaryotic cells. One class of these short molecules are the small interfering RNAs (siRNAs), which after introduction into cells elicit efficient induction of post-transcriptional gene silencing known as RNA interference (RNAi). They are incorporated into a multimeric protein complex named RNA-induced silencing complex (RISC). While one of the two RNA strands is discarded, the antisense strand guides RISC to the complementary target RNA and induces its endonucleolytic cleavage. RNA silencing by post-transcriptional gene silencing (PTGS) is a mechanism of gene regulation in eukaryotes. It is similar to classical humoral immunity, which protects eukaryotes against viruses and transposons. A major problem for the long term inhibition of viruses is the emergence of escape mutants. This limitation, which is well-known for conventional antiviral therapy with low molecular weight drugs, is applicable to RNAi approaches as well. Virus escape as a consequence of the accumulation of point mutations in or close to the siRNA target site has been observed for various types of viruses. To counter this problem a novel technology of production of dsRNAs is used, targeted to essential gene regions for viral replication. The technology is based on the replication complex of the bacteriophage phi 6. A pool of siRNAs is produced in this way, targeted to specific gene region, which overlaps and silences the target, whether a mutation or recombination appear.