Flavin prenyltransferase that catalyzes the synthesis of the prenylated FMN cofactor (prenyl-FMN) for 4-hydroxy-3-polyprenylbenzoic acid decarboxylase UbiD. The prenyltransferase is metal-independent and links a dimethylallyl moiety from dimethylallyl monophosphate (DMAP) to the flavin N5 and C6 atoms of FMN (By similarity). Acts in concert with UbiD to perform the decarboxylation of 4-hydroxy-3-octaprenyl-benzoate, a step in the biosynthesis of coenzyme Q (PubMed:16923914, PubMed:17889824). dimethylallyl phosphate + FMNH2 = phosphate + prenyl-FMNH2 During aerobic growth, expression depends on the carbon source, with the highest expression on succinate, a median expression on glycerol, and the lowest on glucose. During anaerobic growth, glucose does not inhibit expression. Cells lacking this gene produce very low levels of coenzyme Q(8) during logarithmic growth, grow slowly on succinate as the sole carbon source, accumulate 4-hydroxy-3-octaprenyl-benzoate, and have reduced UbiG O-methyltransferase activity. In contrast, they synthesize near normal levels of Q(8) in the stationary phase. Belongs to the UbiX/PAD1 family.