Ubiquinone Biosynthesis in Eukaryotic Cells: Tissue Distribution of mRNA Encoding 3,4-Dihydroxy-5-polyprenylbenzoate Methyltransferase in the Rat and Mapping of the COQ3 Gene to Mouse Chromosome 4

The isolation and sequence of a rat cDNA corresponding to the rat COQ3 gene was recently reported. The COQ3 gene encodes 3,4-dihydroxy-5-polyprenylbenzoate methyltransferase, an enzyme in coenzyme Q biosynthesis. In this study, the rat COQ3 cDNA has been used to examine the expression and chromosomal localization of the COQ3 gene. COQ3 mRNA was detected in every tissue analyzed, consistent with the idea that in most tissues de novo synthesis accounts for the observed levels of Q. Highest levels were present in testis, heart, and skeletal muscle. The rat COQ3 cDNA hybridized to genomic DNA from multiple species, suggesting the conserved nature of the 3,4-dihydroxy-5-polyprenylbenzoate methyltransferase. A single copy of the COQ3 gene appears to be present in rats and mice. By analyzing a restriction fragment length variant in an interspecific backcross, the COQ3 gene was localized to mouse chromosome 4, at a position 3.7 ± 2.6 cM proximal to the marker D4Mit4. The map position of the gene, designated Coq3, places it in close proximity to the mouse vacillans or vc mutation. The symptoms exhibited by the vc mice are similar to those reported for Q deficiencies in humans.