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J. Bacteriol., Mar 1997, 1748-1754, Vol 179, No. 5
PT Lee, AY Hsu, HT Ha and CF Clarke
Strains of Escherichia coli with mutations in the ubiE gene are not able to
catalyze the carbon methylation reaction in the biosynthesis of ubiquinone
(coenzyme Q) and menaquinone (vitamin K2), essential isoprenoid quinone
components of the respiratory electron transport chain. This gene has been
mapped to 86 min on the chromosome, a region where the nucleic acid
sequence has recently been determined. To identify the ubiE gene, we
evaluated the amino acid sequences encoded by open reading frames located
in this region for the presence of sequence motifs common to a wide variety
of S-adenosyl-L-methionine- dependent methyltransferases. One open reading
frame in this region (o251) was found to encode these motifs, and several
lines of evidence that confirm the identity of the o251 product as UbiE are
presented. The transformation of a strain harboring the ubiE401 mutation
with o251 on an expression plasmid restored both the growth of this strain
on succinate and its ability to synthesize both ubiquinone and menaquinone.
Disruption of o251 in a wild-type parental strain produced a mutant with
defects in growth on succinate and in both ubiquinone and menaquinone
synthesis. DNA sequence analysis of the ubiE401 allele identified a
missense mutation resulting in the amino acid substitution of Asp for
Gly142. E. coli strains containing either the disruption or the point
mutation in ubiE accumulated 2-octaprenyl-6-methoxy-1,4- benzoquinone and
demethylmenaquinone as predominant intermediates. A search of the gene
databases identified ubiE homologs in Saccharomyces cerevisiae,
Caenorhabditis elegans, Leishmania donovani, Lactococcus lactis, and
Bacillus subtilis. In B. subtilis the ubiE homolog is likely to be required
for menaquinone biosynthesis and is located within the gerC gene cluster,
known to be involved in spore germination and normal vegetative growth. The
data presented identify the E. coli UbiE polypeptide and provide evidence
that it is required for the C methylation reactions in both ubiquinone and
menaquinone biosynthesis.
Copyright © 1997, American Society for Microbiology
A C-methyltransferase involved in both ubiquinone and menaquinone biosynthesis: isolation and identification of the Escherichia coli ubiE gene
Department of Chemistry and Biochemistry, Molecular Biology Institute, University of California, Los Angeles 90095-1569, USA.
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