Figure 2.

Identification of the components of the base structure of the needle complex. Type III secretion components were isolated from a S. typhimurium invA mutant strain, purified on a CsCl density gradient, and visualized by silver staining (A) or by Western immunoblotting by using an antibody specific to InvG, PrgH, and PrgK (B). The identity of the components is indicated. (C) Electron micrographs of negatively stained purified complexes from the S. typhimurium invA mutant showing the absence of the needle substructure. (Bar = 50 nm.)