Required for efficient ubiquinone (coenzyme Q) biosynthesis under aerobic conditions. UbiK is probably an accessory factor of Ubi enzymes and facilitates ubiquinone biosynthesis by acting as an assembly factor, a targeting factor, or both. Dispensable for ubiquinone biosynthesis under anaerobiosis (PubMed:28559279). Required for proliferation in macrophages and virulence in mice (PubMed:28559279, PubMed:21554724). Significantly contributes to colonization and invasion as well as host inflammation and innate immunity after infection (PubMed:27777572). In vitro, has membrane fusogenic activity at acidic pH (PubMed:21554724). Cofactor biosynthesis; ubiquinone biosynthesis. Homotrimer. Is both soluble and membrane associated inside the cell. Mutant is growth-deficient under aerobic conditions and is impaired to replicate at physiological and high temperatures (PubMed:21554724, PubMed:28559279). Mutant is defective for proliferation in macrophages and mice infection and has a severe attenuation in virulence in the murine model when inoculated both orally and intraperitoneally (PubMed:21554724, PubMed:28559279). Deletion inhibits colonization and invasion of four human cell lines, impairs flagella formation, activates the expression of type-1 fimbriae-like structures on the cell surface, enhances biofilm formation and reduces bacterial motility. The deletion mutant is menaquinone-deficient (PubMed:27777572). Belongs to the UbiK family.