Required for efficient ubiquinone (coenzyme Q) biosynthesis under aerobic conditions (PubMed:28559279, PubMed:30686758). UbiK is probably an accessory factor of Ubi enzymes and facilitates ubiquinone biosynthesis by acting as an assembly factor, a targeting factor, or both (PubMed:28559279). Dispensable for ubiquinone biosynthesis under anaerobiosis (PubMed:28559279). Cofactor biosynthesis; ubiquinone biosynthesis. Homotrimer (PubMed:28559279). 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 the C-terminal part of UbiJ and forms a complex composed of 2 UbiK subunits and 1 UbiJ subunit. The UbiK-UbiJ complex interacts with palmitoleic acid (PubMed:28559279). Deletion of the gene impacts ubiquinone biosynthesis in aerobic conditions but does not decrease menaquinone biosynthesis. Mutant accumulates octaprenylphenol, an early intermediate of the ubiquinone biosynthetic pathway. Belongs to the UbiK family.