Identification of Escherichia coli ubiB, a gene required for the first monooxygenase step in ubiquinone biosynthesis

It was recently discovered that the aarF gene in Providencia stuartii is re quired for coenzyme Q (CoQ) biosynthesis. Here we report that yigR, the Esc herichia coli homologue of aarF, is ubiB, a gene required for the first mon ooxygenase step in CoQ biosynthesis. Both the P. stuartii aarF and E. coli ubiB (yigR) disruption mutant strains lack CoQ and accumulate octaprenylphe nol. Octaprenylphenol is the CoQ biosynthetic intermediate found to accumul ate in the E. coli strain AN59, which contains the ubiB409 mutant allele. A nalysis of the mutation in the E. coli strain AN59 reveals no mutations wit hin the ubiB gene, but instead shows the presence of an ISI element at posi tion +516 of the ubiE gene. The ubiE gene encodes a C-methyltransferase req uired for the synthesis of both CoQ and menaquinone, and it is the 5' gene in an operon containing u6iE, yigP, and ubiB. The data indicate that octapr enylphenol accumulates in AN59 as a result of a polar effect of the ubiE::I S1 mutation on the downstream ubiB gene. AN59 is complemented by a DNA segm ent containing the contiguous ubiE, yigP, and ubiB genes. Although transfor mation of AN59 with a DNA segment containing the ubiB coding region fails t o restore CoQ biosynthesis, transformation with the ubiE coding region resu lts in a low-frequency but significant rescue attributed, to homologous rec ombination. In addition, the fre gene, previously considered to correspond to ubiB, was found not to be involved in CoQ biosynthesis. The ubiB gene is a member of a predicted protein kinase family of which the Saccharomyces c erevisiae ABC1 gene is the prototypic member. The possible protein kinase f unction of UbiB and Abc1 and the role these polypeptides may play in CoQ bi osynthesis are discussed.