Component of the type III secretion system (T3SS), also called injectisome, which is used to inject bacterial effector proteins into eukaryotic host cells (PubMed:12864857, PubMed:29595954). Acts as a regulator of the Spa47/SctN ATPase activity (PubMed:29595954). It down-regulates the ATPase activity of the oligomeric Spa47/SctN, while it up-regulates the activity of the monomeric form (PubMed:29595954). Important for translocation of MxiH/SctF, the major needle component (PubMed:25583506). 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:25583506, PubMed:31699894). This subunit is part of the cytosolic complex (PubMed:18657109, PubMed:25583506, PubMed:31699894). Interacts directly with Spa47/SctN (T3SS ATPase) and Spa33/SctQ (the major sorting platform component) (PubMed:12864857, PubMed:18657109, PubMed:25583506, PubMed:29595954, PubMed:31699894). Homodimer in solution (PubMed:29595954). Inactivation of the gene abolishes the ability of bacteria to assemble a complete type III secretion apparatus (T3SA) and therefore to secrete the translocon proteins IpaB/SctE and IpaC/SctB, and decreases the amounts of the needle filament proteins MxiH/SctF and MxiI/SctI (PubMed:12864857). Mutant is unable to invade HeLa cells (PubMed:12864857).