Figure 3.

The rickettsial Type IV secretion system. The Type IV secretion system (T4SS) from the order Rickettsiales contains eleven distinct subunits termed Rickettsiales vir homologs (Rvh). Notably, the rickettsial T4SS has undergone extensive gene duplication. As a result, the RvhB4, RvhB6, RvhB8 and RvhB9 subunits have multiple paralogs (depicted in color). Also, the RvhB5 subunit is absent from the rickettsial T4SS. OM and IM indicate the rickettsial outer and inner membranes, respectively.