Figure 3.
Effect of overexpression of rpoS-activating sRNAs on acid resistance of Escherichia coli. (A) Acid resistance of E. coli cells overexpressing DsrA, RprA, and ArcZ, respectively, was examined. Survival rates of exponentially growing or stationary-phase cells after exposure to pH 2.0 for 1 h were determined. Overexpression of sRNAs was induced by 1.0 mmol/L IPTG. Values are averaged from at least three independent experiments. Tenfold serial dilutions of cultures exposed to acid challenge were additionally spotted on LB agar and grown overnight. (B) β-Galactosidase activities from cells containing a rpoS-lacZ translational fusion (SG30013) were measured upon sRNA overexpression at the exponential or stationary phase. (C) Overexpression of rpoS-activating sRNAs from the corresponding RNA expression plasmids was confirmed using Northern blot analysis. Antisense oligonucleotides for ArcZ, DsrA, and RprA were mixed, labeled with 32P, and used as probes.