EVIDENCE THAT ESCHERICHIA-COLI UBIA PRODUCT IS A FUNCTIONAL HOMOLOG OF YEAST COQ2, AND THE REGULATION OF UBIA GENE-EXPRESSION

The Escherichia coli ubiA gene coding for 4-hydroxy benzoate octaprenyl transferase is thought to be a key enzyme of ubiquinone biosynthesis. Strains with ubiA disrupted were constructed by chromosomal gene replacement with the chloramphenicol resistance gene. The respiration-defective phenotype of the ubiA mutant was complemented by expression of the COQ2 gene encoding the 4-hydroxy benzoate hexaprenyl transferase of Saccharomyces cevevisiae and such strains produced ubiquinone-8. This strongly supports the idea that COQ2 catalyzes the same enzymatic reaction with UbiA and the substrate specificity of COQ2 is broad. Study of the expression of ubiA using an ubiA-lacZ fusion system showed that the ubiA expression was catabolite-repressed by glucose. This repression by glucose was obvious in the arcA mutant. ArcA is the positively acting transcriptional regulator of the oxygen regulated genes. The molecular mass of the protein product of ubiA was 32 kD, found using the over-expression of the ubiA gene.