Table 1. Genes required for ubiquinone biosynthesis or function.

Yeast genes required for UQ biosynthesis (COQ1-9, ARH1 and YAH1) or UQ function in respiration (COQ10) and their homologues in higher eukaryotes are presented. ARH1 and YAH1 are found to be required for the C5-hydroxylation reaction. The functions in UQ₆ biosynthesis of these two genes as well as those of three COQ genes (COQ4, COQ8 and COQ9) are not yet understood. For E. coli, only the genes that are functionally equivalent to yeast COQ genes are shown, including four genes whose products share homology with yeast Coq proteins (Okada et al., 1996, Hsu et al., 1996, Dibrov et al., 1997, Suzuki et al., 1994) and ubiF which catalyzes the same reactions as the COQ7 genes but bears no homology to them (Tran et al., 2006).

Function	Genes
	S. cerevisiae	C. elegans	M. musculus	H. sapiens	E. coli
Elongation of prenyl side-chain	COQ1	coq-1	Pdss1/Pdss2	PDSS1/PDSS2	ispB*
Prenalytion of ring precursor	COQ2	coq-2	Coq2	COQ2*	ubiA
O5 and O6 methylation	COQ3	coq-3	Coq3	COQ3*	ubiG*
unknown	COQ4	coq-4	Coq4	COQ4*	-
C2-methylation	COQ5	coq-5*	Coq5	COQ5	ubiE
C5-hydroxylation	COQ6	coq-6	Coq6	COQ6*	-
C6-hydroxylation	COQ7	coq-7/clk-1*	Coq7/Mclk1	COQ7*	ubiF*
unknown	COQ8	Coq-8	Coq8	ADCK3*	-
unknown	COQ9	-	Coq9	COQ9	-
unknown	COQ10	-	Coq10a/Coq10b	COQ10A/10B	-
unknown	ARH1	-	-	-	-
unknown	YAH1	-	-	-	-

Asterisks indicate that genes have been shown to functionally complement corresponding yeast mutants.