Figure 1.

Steady-state levels of RpoS determined by quantitative western-blotting in the wt strain and the isogenic csdA mutant. The E. coli strains WJW45 (wt), the isogenic csdA deficient strain WJW45ΔcsdA (csdA⁻) as well as WJW45ΔcsdA harbouring plasmid pUCdeaD³⁸ (csdA⁻/pUCdeaD) were grown to early log phase (OD₆₀₀ of 0.4) either at 37°C (lane 2–4) or at 24°C (lane 5–7), respectively. Cell extracts of the rpoS mutant strain RH90,⁵³ served as a negative control (lane 1). Equal amounts of total cellular proteins were loaded in each lane of the SDS-polyacrylamide gel. The RpoS protein was detected by immunological means as described in Materials and Methods. Only the relevant section of the immunoblot is shown.