Fig 1.

Proposed biosynthetic pathway of RQ (compound 1). Known Coq (from yeast) and Ubi (from E. coli) gene products required for the biosynthesis of Q (compound 2) are labeled. The pathways for yeast and E. coli both utilize p-hydroxybenzoic acid (compound 6) as an early precursor and merge again at the common intermediate (compound 8). For R. rubrum, we have shown that Q is a precursor to RQ. The number of isoprene units (n) varies by species (S. cerevisiae [yeast], n = 6; E. coli, n = 8; C. elegans and E. gracilis, n = 9; helminth parasites, n = 9 or 10; R. rubrum, n = 10; humans, n = 10). RQ is not found in yeast, E. coli, or humans.