Fig. 5.

Inactive ExbB mutants assemble correctly with TonB. Equivalent numbers of mid-exponential-phase bacteria were cross-linked with paraformaldehyde and evaluated by immunoblotting with anti-TonB antibody. Wild-type W3110 (WT), the parent strain for all of the plasmid variants RA1017 (ΔexbBD ΔtolQRA), the parent plasmid encoding both ExbB and ExbD (pExbBD), and the plasmids expressing the ExbB variants are indicated above each lane of the immunoblot. The lower panel is a shorter exposure of the upper panel to allow evaluation of the monomer TonB levels. The positions of the TonB monomer, the TonB-Lpp heterodimer, the TonB-ExbB heterodimer, and the TonB-FepA heterodimer are indicated on the right. The positions of mass standards are indicated on the left.