C. BS3 cross-linking assay. 2×109 cells of the indicated strain producing FLAG-tagged TssM (with the exception of ∆tssM cells) were treated (+) or not (-) with the BS3 cross-linker agent. After the cross-linking reaction, cells were boiled in Laemmli buffer and total proteins were subjected to 7%-acrylamide SDS-PAGE and immunodetected with anti-FLAG antibodies. The TssM protein (FLTssM) and its complexes (*, TssM-TssJ; **, TssM-TssL) are indicated on the right as well as the TssM dimer (arrow). Molecular weight markers (in kDa) are indicated on the left. The experiment was performed in triplicate and a representative result is shown. 