title: Genetic evidence for a multi-subunit complex in the O-methyltransferase steps of coenzyme Q biosynthesis.
abstract: Coq3 O-methyltransferase carries out both O-methylation steps in coenzyme Q (ubiquinone) biosynthesis. The degree to which Coq3 O-methyltransferase activity and expression are dependent on the other seven COQ gene products has been investigated. A panel of yeast mutant strains harboring null mutations in each of the genes required for coenzyme Q biosynthesis (COQ1-COQ8) have been prepared. Mitochondria have been isolated from each member of the yeast coq mutant collection, from the wild-type parental strains and from respiratory deficient mutants harboring deletions in ATP2 or COR1 genes. These latter strains constitute Q-replete, respiratory deficient controls. Each of these mitochondrial preparations has been analyzed for COQ3-encoded O-methyltransferase activity and steady state levels of Coq3 polypeptide. The findings indicate that the presence of the other COQ gene products is required to observe normal levels of O-methyltransferase activity and the Coq3 polypeptide. However, COQ3 steady state RNA levels are not decreased in any of the coq mutants, relative to either wild-type or respiratory deficient control strains, suggesting either a decreased rate of translation or a decreased stability of the Coq3 polypeptide. These data are consistent with the involvement of the Coq polypeptides (or the Q-intermediates formed by the Coq polypeptides) in a multi-subunit complex. It is our hypothesis that a deficiency in any one of the COQ gene products results in a defective complex in which the Coq3 polypeptide is rendered unstable.
authors.affiliation: Department of Chemistry and Biochemistry and the Molecular Biology Institute, University of California, Los Angeles, CA 90095-1569, USA.
authors.forename: A Y
authors.initials: AY
authors.lastname: Hsu
authors.forename: T Q
authors.initials: TQ
authors.lastname: Do
authors.forename: P T
authors.initials: PT
authors.lastname: Lee
authors.forename: C F
authors.initials: CF
authors.lastname: Clarke
mesh_terms: D004795:Enzyme Stability / Q000235:genetics; D017353:Gene Deletion; D005838:Genotype; D008780:Methyltransferases / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D009154:Mutation; D012313:RNA / Q000096:biosynthesis; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics; D014451:Ubiquinone / Q000096:biosynthesis* / Q000737:chemistry / Q000172:deficiency
chemical_list: C028325:ubiquinone Q3; D014451:Ubiquinone; D012313:RNA; D008780:Methyltransferases; C070696:3,4-dihydroxy-5-hexaprenylbenzoate methyltransferase