TprC and TprI, but not TprF, expressed in E. coli with PelB signal sequences fractionate with OMs and display bipartite topology. Comparable portions of periplasmic (P), inner membrane (IM), and outer membrane (OM) fractions, generated as described under “Experimental Procedures,” were subjected to SDS-PAGE and immunoblotting with antisera directed against ATP synthase B subunit (ATPB), Skp, and OmpA as markers for the IM, P, and OM fractions, respectively (A), and TprC (for E. coli expressing TprC and TprI) or TprCN (for E. coli expressing TprF) (B). C, IFA of intact (I) or permeabilized (P) E. coli C41 (DE3) expressing TprC, TprI, or TprF with PelB signal sequence were probed with 1:1,000 dilutions of rat antisera against TprCN, TprCC, and Skp (periplasmic control). Antibody binding was detected with 1 μg/ml goat anti-rat Alexa Fluor 488 conjugate.