Design and Cloning of an shRNA into a Lentiviral Silencing Vector: Version A.

INTRODUCTIONThis protocol combines the specificity of small interfering RNA (siRNA)-mediated silencing cassettes with the versatility of lentiviral vectors to stably transduce a wide range of cell types. A short hairpin RNA (shRNA) designed against a given target is cloned into a plasmid containing the pol III promoter. The design uses a 5' forward primer upstream of the pol III promoter and a 3' reverse primer that includes the entire shRNA sequence (i.e., sense, loop, and antisense sequences followed by five Ts), followed by 22 bases complementary to the last 22 bp upstream of the +1 transcriptional start site of the pol III promoter. An NheI-compatible restriction site is included at the 5' end of both forward and reverse primers. A single round of PCR is used to amplify this template. The resulting DNA fragment contains an shRNA expression cassette that can be cloned into a simple cloning vector, tested, and then transferred to the lentiviral vector, or cloned into the lentiviral vector directly. This procedure uses a unique restriction site in the 3' long terminal repeat (LTR). During integration, the 5' LTR of the provirus is copied from the 3' LTR, cloning the H1-driven shRNA into the 3' LTR, resulting in duplication of the silencing cassette. This strategy maximizes the silencing power of the lentiviral vector. The combination of the lentiviral and siRNA technologies provides a powerful tool to achieve long-term down-regulation of specific target genes both in vitro and in vivo.