Figure 3: Using ASRE to silence gene expression in E. coli.

(a) The activity of β-galactosidase (β-gal) in E. coli strains transformed with ASRE(LacZ) plasmid and control plasmids. For each strain, the β-gal activity from multiple independent clones (N=2 or 5) in triplicate experiments was measured. The relative β-gal activity was normalized to clones transformed with the empty vector and induced with the same condition. The uninduced clones containing empty vector was used as the baseline activity. Error bars represent the s.e. across all clones. (b) The levels of lacZ mRNA were measured by quantitative RT–PCR. The samples were in the same order as panel a. LacZ levels were normalized to ftsZ mRNA, and the relative RNA abundances compared with uninduced controls are plotted. Error bars represent the s.e. across all clones. (c) The effect of ASREs on other mRNAs containing similar recognition sites. The E. coli strains transformed with ASRE(LacZ) or empty vector were induced with IPTG, and the RNA levels were measured with quantitative RT–PCR. The relative RNA abundances compared with vector controls are plotted. Two independent clones were selected in each strain, and the inductions were carried out in triplicates. Error bars represent the standard derivations.