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Gene Review

COQ3  -  hexaprenyldihydroxybenzoate methyltransferase

Saccharomyces cerevisiae S288c

Synonyms: 2-polyprenyl-6-hydroxyphenol methylase, 3,4-dihydroxy-5-hexaprenylbenzoate methyltransferase, 3-demethylubiquinone-6 3-methyltransferase, DHHB methyltransferase, DHHB-MT, ...
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Disease relevance of COQ3

  • The hypersensitivity of the coq3delta strains can be prevented by the presence of the COQ3 gene on a single copy plasmid, indicating that the sensitive phenotype results solely from the inability to produce Q [1].
  • An additional conserved motif was shared by these viral proteins and two distinct groups of methyltransferases including as the prototypes Rhodobacter capsulatus hydroxyneurosporene methylase (crtF gene product) and yeast 3,4-dihydroxy-5-hexaprenylbenzoate methylase (COQ3 gene product), respectively [2].
  • Yeast and rat Coq3 and Escherichia coli UbiG polypeptides catalyze both O-methyltransferase steps in coenzyme Q biosynthesis [3].
  • The predicted amino acid sequence contained all consensus regions for S-adenosyl methionine methyltransferases and presented 26% identity with Saccharomyces cerevisiae DHHB-methyltransferase and 38% identity with the rat protein, as well as with a bacterial (Escherichia coli and Salmonella typhimurium) methyltransferase encoded by the UBIG gene [4].
  • Statistically significant similarity was revealed between the region of flavivirus NS5 containing the SAM-binding motif and a newly characterized family of putative methyltransferases from bacteria, yeast and plants, which is related to the Coq3 group [2].

High impact information on COQ3

  • Here we show that addition of Q to the growth media also stabilizes the Coq3 and Coq4 polypeptides in the coq7 null mutant [5].
  • Coq3 and Coq4 define a polypeptide complex in yeast mitochondria for the biosynthesis of coenzyme Q [6].
  • Isolation and functional expression of human COQ3, a gene encoding a methyltransferase required for ubiquinone biosynthesis [7].
  • The clone contained a 933-base pair open reading frame that encoded a polypeptide with a great deal of sequence identity to a variety of eukaryotic and prokaryotic Coq3 homologues [7].
  • A full-length cDNA encoding the human homologue of COQ3 was isolated from a human heart cDNA library by sequence homology to rat Coq3 [7].

Biological context of COQ3

  • Specifically, rho0 mutants that lack mitochondrial DNA, and strains deleted for the nuclear genes COX6 and COQ3 that are required for function of the respiratory electron transport chain, were sensitive to H2O2 [8].
  • The sequence contains 13 open reading frames (ORFs) of which four encode the known genes ADH1, COQ3, MSH2 and RCF4 [9].
  • Both coenzyme Q6 and NADH-ascorbate free radical reductase were rescued in plasma membranes derived from a strain obtained by transformation of the coq3delta strain with a single-copy plasmid bearing the wild type COQ3 gene and in plasma membranes isolated form the coq3delta strain grown in the presence of coenzyme Q6 [10].
  • A full length cDNA encoding a homologue of DHHB-methyltransferase was cloned from an Arabidopsis thaliana cDNA library by functional complementation of a yeast coq3 deletion mutant [4].

Anatomical context of COQ3


Associations of COQ3 with chemical compounds

  • Strains containing respiration-deficient mutations in genes such as COQ3, required for the synthesis of coenzyme Q, were reduced in their ability to accumulate glycogen in response to limiting glucose [12].
  • COQ3 encodes a 3,4-dihydroxy-5-hexaprenylbenzoate (DHHB) methyltransferase that catalyses the fourth step in the biosynthesis of ubiquinone from p-hydroxybenzoic acid [4].
  • The CoQ6-independent reduction of ascorbate free radical was not due to copper uptake, pH changes or to the presence of CoQ6 biosynthetic intermediates, but decreased to undetectable levels when coq3 mutant strains were cultured in media supplemented with ferric iron [13].
  • In eukaryotes, the first O-methylation step is carried out by the Coq3 polypeptide, which catalyzes the transfer of a methyl group from S-adenosylmethionine to 3,4-dihydroxy-5-polyprenylbenzoate [14].

Other interactions of COQ3

  • In contrast, deletion of PCL8 and PCL10 in the coq3 mutant background partially restores glycogen accumulation [15].


  1. Enhanced sensitivity of ubiquinone-deficient mutants of Saccharomyces cerevisiae to products of autoxidized polyunsaturated fatty acids. Do, T.Q., Schultz, J.R., Clarke, C.F. Proc. Natl. Acad. Sci. U.S.A. (1996) [Pubmed]
  2. Computer-assisted identification of a putative methyltransferase domain in NS5 protein of flaviviruses and lambda 2 protein of reovirus. Koonin, E.V. J. Gen. Virol. (1993) [Pubmed]
  3. Yeast and rat Coq3 and Escherichia coli UbiG polypeptides catalyze both O-methyltransferase steps in coenzyme Q biosynthesis. Poon, W.W., Barkovich, R.J., Hsu, A.Y., Frankel, A., Lee, P.T., Shepherd, J.N., Myles, D.C., Clarke, C.F. J. Biol. Chem. (1999) [Pubmed]
  4. Cloning and functional expression of AtCOQ3, the Arabidopsis homologue of the yeast COQ3 gene, encoding a methyltransferase from plant mitochondria involved in ubiquinone biosynthesis. Avelange-Macherel, M.H., Joyard, J. Plant J. (1998) [Pubmed]
  5. Complementation of Saccharomyces cerevisiae coq7 mutants by mitochondrial targeting of the Escherichia coli UbiF polypeptide: two functions of yeast Coq7 polypeptide in coenzyme Q biosynthesis. Tran, U.C., Marbois, B., Gin, P., Gulmezian, M., Jonassen, T., Clarke, C.F. J. Biol. Chem. (2006) [Pubmed]
  6. Coq3 and Coq4 define a polypeptide complex in yeast mitochondria for the biosynthesis of coenzyme Q. Marbois, B., Gin, P., Faull, K.F., Poon, W.W., Lee, P.T., Strahan, J., Shepherd, J.N., Clarke, C.F. J. Biol. Chem. (2005) [Pubmed]
  7. Isolation and functional expression of human COQ3, a gene encoding a methyltransferase required for ubiquinone biosynthesis. Jonassen, T., Clarke, C.F. J. Biol. Chem. (2000) [Pubmed]
  8. Mitochondrial function is required for resistance to oxidative stress in the yeast Saccharomyces cerevisiae. Grant, C.M., MacIver, F.H., Dawes, I.W. FEBS Lett. (1997) [Pubmed]
  9. A 29.425 kb segment on the left arm of yeast chromosome XV contains more than twice as many unknown as known open reading frames. Zumstein, E., Pearson, B.M., Kalogeropoulos, A., Schweizer, M. Yeast (1995) [Pubmed]
  10. Genetic evidence for coenzyme Q requirement in plasma membrane electron transport. Santos-Ocaña, C., Villalba, J.M., Córdoba, F., Padilla, S., Crane, F.L., Clarke, C.F., Navas, P. J. Bioenerg. Biomembr. (1998) [Pubmed]
  11. Cloning of a rat cDNA encoding dihydroxypolyprenylbenzoate methyltransferase by functional complementation of a Saccharomyces cerevisiae mutant deficient in ubiquinone biosynthesis. Marbois, B.N., Hsu, A., Pillai, R., Colicelli, J., Clarke, C.F. Gene (1994) [Pubmed]
  12. Mitochondrial respiratory mutants in yeast inhibit glycogen accumulation by blocking activation of glycogen synthase. Yang, R., Chun, K.T., Wek, R.C. J. Biol. Chem. (1998) [Pubmed]
  13. Coenzyme Q6 and iron reduction are responsible for the extracellular ascorbate stabilization at the plasma membrane of Saccharomyces cerevisiae. Santos-Ocaña, C., Córdoba, F., Crane, F.L., Clarke, C.F., Navas, P. J. Biol. Chem. (1998) [Pubmed]
  14. Complementation of coq3 mutant yeast by mitochondrial targeting of the Escherichia coli UbiG polypeptide: evidence that UbiG catalyzes both O-methylation steps in ubiquinone biosynthesis. Hsu, A.Y., Poon, W.W., Shepherd, J.A., Myles, D.C., Clarke, C.F. Biochemistry (1996) [Pubmed]
  15. Analysis of respiratory mutants reveals new aspects of the control of glycogen accumulation by the cyclin-dependent protein kinase Pho85p. Wilson, W.A., Wang, Z., Roach, P.J. FEBS Lett. (2002) [Pubmed]
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