| Abstrakt: |
Ubiquinone (coenzyme Q) is a lipid that transports electrons in the respiratory chains of both prokaryotes and eukaryotes. Mutants of Saccharomyces cerevisiaedeficient in ubiquinone biosynthesis fail to grow on nonfermentable carbon sources and have been classified into eight complementation groups (coq1-coq8; Tzagoloff, A., and Dieckmann, C. L.(1990) Microbiol. Rev.54, 211-225). In this study we show that although yeast coq7mutants lack detectable ubiquinone, the coq7-1mutant does synthesize demethoxyubiquinone (2-hexaprenyl-3-methyl-6-methoxy-1,4-benzoquinone), a ubiquinone biosynthetic intermediate. The corresponding wild-type COQ7gene was isolated, sequenced, and found to restore growth on nonfermentable carbon sources and the synthesis of ubiquinone. The sequence predicts a polypeptide of 272 amino acids which is 40% identical to a previously reported Caenorhabditis elegansopen reading frame. Deletion of the chromosomal COQ7gene generates respiration defective yeast mutants deficient in ubiquinone. Analysis of several coq7deletion strains indicates that, unlike the coq7-1mutant, demethoxyubiquinone is not produced. Both coq7-1and coq7deletion mutants, like other coqmutants, accumulate an early intermediate in the ubiquinone biosynthetic pathway, 3-hexaprenyl-4-hydroxybenzoate. The data suggest that the yeast COQ7gene may encode a protein involved in one or more monoxygenase or hydroxylase steps of ubiquinone biosynthesis. |
