( Ambion's newest...)Drive Long-Term Silencing with CMV Vectors

Ambion's newest line of plasmid siRNA expression vectors, pSilencer 4.1-CMV, feature polymerase (pol) II promoters that drive transcription of both an siRNA template and an antibiotic resistance gene. The CMV promoter is used to drive siRNA expression. This strong promoter is active in a broad range of cell types and performs better than most pol III promoters under long term selection.

One use of plasmid-based siRNA expression vectors is for long term gene silencing studies in mammalian cells. Typically these vectors encode a hairpin siRNA under the control of a polymerase III promoter and an antibiotic resistance gene driven by a polymerase II promoter. While it is possible to use such vectors to produce stable cell lines expressing siRNAs that silence their targets, there are, to date, very few published accounts of doing so (Xia 2002). One explanation for the difficulty in producing such clones is possible interference between the pol II and III promoters. Although the exact mechanism is not understood, it is hypothesized that when pol II and III promoters are in close proximity, interference of transcription between the two promoters can occur. This suggests that clones derived from a transfection/selection experiment will either express the siRNA or the antibiotic resistance gene but rarely express both. To overcome this potential problem, we have constructed three '"/>

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