Involved in the synthesis of the type III secretion system (T3SS), also called injectisome, which is used to inject bacterial effector proteins into eukaryotic host cells (PubMed:9427408, PubMed:15292137). Pilot protein that is required for the proper localization of the secretin YscC/SctC in the outer membrane (PubMed:9427408, PubMed:15292137). Also required for efficient oligomerization of YscC/SctC and stabilization of the oligomers (PubMed:15292137). Interacts with YscC/SctC. Association with the outer membrane is a prerequisite for function in the biogenesis of YscC/SctC. In mutant, only a small amount of YscC/SctC is properly targeted to the outer membrane (PubMed:9427408, PubMed:15292137). Mutant is Ca(2+) independent for growth at 37 degrees Celsius and secretes smaller amounts of Yop proteins (PubMed:7635810). Belongs to the ExsB/YscW family.