Required for ubiquinone (coenzyme Q) biosynthesis under aerobic conditions (PubMed:24142253, PubMed:30686758). Binds hydrophobic ubiquinone biosynthetic intermediates via its SCP2 domain and is essential for the stability of the Ubi complex (PubMed:30686758). May constitute a docking platform where Ubi enzymes assemble and access their SCP2-bound polyprenyl substrates (PubMed:30686758). Cofactor biosynthesis; ubiquinone biosynthesis. Component of the Ubi complex metabolon, which regroups five ubiquinone biosynthesis proteins (UbiE, UbiF, UbiG, UbiH and UbiI) and two accessory factors (UbiK and the lipid-binding protein UbiJ) (PubMed:30686758). Interacts with UbiK and forms a complex composed of 2 UbiK subunits and 1 UbiJ subunit. The UbiK-UbiJ complex interacts with palmitoleic acid (PubMed:28559279). 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. Belongs to the UbiJ family.