Timmons and Fire [4] first described a method for RNAi in which bacteria expressing dsRNA are fed to C. elegans. A fragment corresponding to the gene of interest is cloned into a feeding vector (L4440) between two T7 promoters in inverted orientation and is transformed into a bacterial strain carrying IPTG-inducible expression of T7 polymerase [4]. Recently, Timmons and Fire also showed that use of an E. coli strain (HT115(DE3)), which lacks double-strand-specific RNase III, improves the ability to produce RNAi phenotypes by feeding (L. Timmons and A. Fire, personal communication; and Figure 1).
