Required for ubiquinone (coenzyme Q) biosynthesis under aerobic conditions (PubMed:24142253). Binds hydrophobic ubiquinone biosynthetic intermediates via its SCP2 domain and is essential for the stability of the Ubi complex (By similarity). May constitute a docking platform where Ubi enzymes assemble and access their SCP2-bound polyprenyl substrates (By similarity). Required for intracellular proliferation in macrophages (PubMed:24142253). Cofactor biosynthesis; ubiquinone biosynthesis. During aerobic growth, mutant is impaired for ubiquinone biosynthesis and for growth in rich medium, but it does not present any defect under anaerobic conditions. Mutant is also impaired for Salmonella intracellular proliferation in macrophages. Belongs to the UbiJ family.