Component of the type III secretion system (T3SS), also called injectisome, which is used to inject bacterial effector proteins into eukaryotic host cells (PubMed:28283062). Acts as a regulator of the InvC/SctN1 ATPase activity (By similarity). Required for invasion and secretion (PubMed:10816487). The core secretion machinery of the T3SS is composed of approximately 20 different proteins, including cytoplasmic components, a base, an export apparatus and a needle (PubMed:30107569, PubMed:28283062). This subunit is part of the cytosolic complex (PubMed:28283062, PubMed:31288030). Interacts directly with InvC/SctN1 (T3SS-1 ATPase) and SpaO/SctQ (the major sorting platform component) (PubMed:15060043, PubMed:25994170, PubMed:28283062, PubMed:31288030). Forms homodimers (PubMed:31288030). Deletion of the gene disrupts proper SpaO/SctQ localization.