 C. SecB physically interacts with proOmpA. proOmpA1 (5 μM) was incubated (50 μl; Buffer C; < 0.2 M urea; 4°C; 60 min), with the indicated molar excess of SecB4 (filled arrow), analyzed by native-PAGE as in Fig. 2A, and stained as indicated. brace: higher order proOmpA species. Representative experiment shown; n= 5 biological replicates 