A C-METHYLTRANSFERASE INVOLVED IN BOTH UBIQUINONE AND MENAQUINONE BIOSYNTHESIS - ISOLATION AND IDENTIFICATION OF THE ESCHERICHIA-COLI UBIE GENE

Strains of Escherichia coli with mutations in the ubiE gene are not ab le to catalyze the carbon methylation reaction in the biosynthesis of ubiquinone (coenzyme Q) and menaquinone (vitamin K-2), essential isopr enoid 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 th e ubiE gene, we evaluated the amino acid sequences encoded by open rea ding frames located in this region for the presence of sequence motifs common to a wide variety of S-adenosyl-L-methionine-dependent methylt ransferases. One open reading frame in this region (o251) was found to encode these motifs, and several lines of evidence that confirm the i dentity 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 a bility to synthesize both ubiquinone and menaquinone. Disruption of o2 51 in a wild-type parental strain produced a mutant with defects in gr owth on succinate and in both ubiquinone and menaquinone synthesis. DN A sequence analysis of the ubiE401 allele identified a missense mutati on resulting in the amino acid substitution of Asp for Gly(142). E. co li strains containing either the disruption or the point mutation in u biE accumulated 2-octaprenyl-6-methoxy-1,4-benzoquinone and demethylme naquinone as predominant intermediates. A search of the gene databases identified ubiE homologs in Saccharomyces cerevisiae, Caenorhabditis elegans, Leishmania donovani, Lactococcus lactis, and Bacillus subtili s. In B. subtilis the ubiE homolog is likely to be required for menaqu inone 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 evide nce that it is required for the C methylation reactions in both ubiqui none and menaquinone biosynthesis.