Contains FAD. The enzyme from the bacterium Escherichia coli (UbiI) catalyses the first hydroxylation during the aerobic biosynthesis of ubiquinone. The enzyme from the bacterium Neisseria meningitidis (UbiM) can also catalyse the two additional hydroxylations that occur in the pathway (cf. EC 1.14.99.60, 3-demethoxyubiquinol 3-hydroxylase).