Cloning and characterization of a gene from Escherichia coli encoding a transketolase-like enzyme that catalyzes the synthesis of d-1-deoxyxylulose 5-phosphate, a common precursor for isoprenoid, thiamin, and pyridoxol biosynthesis

For many years it was accepted that isopentenyl diphosphate, the common precursor of all isoprenoids, was synthesized through the well known acetate/mevalonate pathway. However, recent studies have shown that some bacteria, including Escherichia coli, use a mevalonate-independent pathway for the synthesis of isopentenyl diphosphate. The occurrence of this alternative pathway has also been reported in green algae and higher plants. The first reaction of this pathway consists of the condensation of (hydroxyethyl)thiamin derived from pyruvate with the C1 aldehyde group of d-glyceraldehyde 3-phosphate to yield d-1-deoxyxylulose 5-phosphate. In E. coli, d-1-deoxyxylulose 5-phosphate is also a precursor for the biosynthesis of thiamin and pyridoxol. Here we report the molecular cloning and characterization of a gene from E. coli, designated dxs, that encodes d-1-deoxyxylulose-5-phosphate synthase. The dxs gene was identified as part of an operon that also contains ispA, the gene that encodes farnesyl-diphosphate synthase. d-1-Deoxyxylulose-5-phosphate synthase belongs to a family of transketolase-like proteins that are highly conserved in evolution.