Short interfering RNAs as tools for sequence-specific gene silencing

In diverse eukaryotes, dsRNA triggers the destruction of mRNA sharing thesame sequence as the dsRNA in the process called RNAi. The guides for sequence-specific degradation of mRNA are 21 nt short interfering RNAs (siRNAs).Synthetic siRNAs can efficiently mediate RNAi, but a drawback of RNAi is itstransient nature as a result of the limited availability and stability of syntheticoligonucleotides. Recently, several groups reported the construction of expression plasmid vectors that mediate the production of siRNAs under control ofPol III promoters. These vectors allow the continued expression of siRNAs in thecells resulting in persistent and specific suppression of target genes. The retroviralsiRNA expressing system allows for stable inactivation of the genes in primarycells or living organisms.