Biochemical and Genetic Studies on Ubiquinone Biosynthesis in Escherichia coli K-12: 4-Hydroxybenzoate Octaprenyltransferase

Abstract

Three ubiquinone-deficient mutants of Escherichia coli unable to convert 4-hydroxybenzoate into 3-octaprenyl-4-hydroxybenzoate were isolated and examined. The results of genetic analysis suggest that each of the mutants carries a mutation in a gene designated ubiA which can be represented at minute 79 on the E. coli chromosome map. The conversion of 4-hydroxybenzoate into 3-octaprenyl-4-hydroxybenzoate, catalyzed by 4-hydroxybenzoate octaprenyltransferase, was studied with a strain of E. coli that is blocked in the common pathway of aromatic biosynthesis and consequently accumulates the precursor of the side chain of ubiquinone. Both the side-chain precursor and 4-hydroxybenzoate octaprenyltransferase were shown to be membrane-bound. The enzyme required Mg 2+ for optimal activity. The ubiA − mutants were found to lack 4-hydroxybenozate octaprenyltransferase activity, which suggested that the ubiA gene is the structural gene coding for this enzyme.