FIG. 4.

The effect of the H107A substitution in σ³² on cell growth. All growth curves are for E. coli strain CAG9301 in which the endogenous σ³² was inactivated (minus-σ³² strain). The strains differ in whether they contain plasmid expressing WT σ³², plasmid expressing H107A σ³², or no plasmid. Expression of the σ³² genes was driven by the basal transcription activity from the lac promoter; no IPTG inducer was added. (A) Growth at 32°C. (B) Initial growth at 32°C, followed by a shift in temperature from 32 to 42°C 1.5 h after inoculation of the culture.