Fig. 3.

VexE is required for efficient export and surface retention of Vi antigen. (A) The Vi antigen depolymerase was unable to access Vi antigen within intact cells of the ΔvexE mutant. Whole or lysed cells of S. Typhi and mutants were incubated with purified VexL, collected, digested with proteinase K, and probed for Vi antigen. VexL was able to degrade the Vi antigen in wild-type S. Typhi but not in S. Typhi ΔvexC, providing positive and negative controls for export, respectively. (B) Immunofluorescence microscopy of cells probed with anti-Vi antigen antibodies illustrated that the ΔvexE mutant possessed no Vi antigen on its surface but accumulated intracellular Vi antigen in inclusion bodies, which became accessible to antibody in permeabilized cells. (Scale bars, 10 µm.) Insets are enlarged to show a representative cell. (C) S. Typhi ΔvexE was able to export Vi antigen in a transporter-dependent manner. Growth medium from early exponential-phase cultures was collected and probed for Vi antigen and (cytosolic) RNA polymerase by Western immunoblotting.