FIG. 4.

Effect of TonB on T7-ExbB and T7-ExbD complex formation. Strains KP1269 (ΔexbBD) and KP1346 (ΔexbBD ΔtonB) carrying plasmids pKP360 (ExbD) and/or pKP339 (T7-ExbB), pKP361 (ExbB) and/or pKP323 (T7-ExbD), pACYC184 and pET-24(a)+ (vector controls), or pKP298 and pET-24(a)+ (ExbBD) were cross-linked in vivo by using standard formaldehyde as described in Materials and Methods. Samples representing equal cell numbers were electrophoresed on SDS–11% polyacrylamide gels, and complexes containing T7 epitope-tagged proteins were detected by immunoblot analysis with anti-T7 epitope tag monoclonal antibody. +, strain containing tonB; −, strain in which tonB has been deleted; ∗, cross-reactive band.