Figure 3. SurA is required for wild-type levels of LptD.

A. Levels of LptD, LamB, and OmpA, three integral β-barrel proteins, were monitored by Western blotting in MC4100 and its ΔsurA::kan derivative CB47 cells in logarithmic (OD₆₀₀~0.45) and stationary phase (overnight cultures). In both growth phases, all three proteins are decreased in cells lacking SurA, but the decrease in LptD levels is the most dramatic.

B. Lack of SurA increases the synthesis of lptDsurA. Synthesis of a lptDsurA’-’lacZ⁺ fusion was monitored in NR778, a strain carrying surA under the control of the P_ara promoter and surA’-’lacZ under the native promoter of the lptDsurA operon. When arabinose is present in the growth medium, this strain is SurA⁺ but in the absence of arabinose, it lacks SurA and LacZ activity increases.