Characterization of the COQ5 Gene from Saccharomyces cerevisiae EVIDENCE FOR A C-METHYLTRANSFERASE IN UBIQUINONE BIOSYNTHESIS*

Ubiquinone (coenzyme Q or Q) is a lipophilic metabo-lite that functions in the electron transport chain in the plasma membrane of prokaryotes and in the inner mito-chondrial membrane of eukaryotes. Q-deficient mutants of Saccharomyces cerevisiae fall into eight complemen-tation groups (coq1–coq8). Yeast mutants from the coq5 complementation group lack Q and as a result are res-piration-defective and fail to grow on nonfermentable carbon sources. A nuclear gene, designated COQ5 was isolated from a yeast genomic library based on its ability to restore growth of a representative coq5 mutant on media containing glycerol as the sole carbon source. The DNA segment responsible for the complementation con-tained an open reading frame (GenBankTM accession number Z49210) with 44 % sequence identity over 26