CLONING AND CHARACTERIZATION OF A GENE FROM ESCHERICHIA-COLI ENCODINGA 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 commo n precursor of all isoprenoids, was synthesized through the well known acetate/mevalonate pathway, However, recent studies have shown that s ome 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 cond ensation of (hydroxyethyl)thiamin derived from pyruvate with the C1 al dehyde group of D-glyceraldehyde 3-phosphate to yield D-1-deoxyxylulos e 5-phosphate, In E. coli, D-1-deoxyxylulose 5-phosphate is also a pre cursor for the biosynthesis of thiamin and pyridoxol, Here we report t he molecular cloning and characterization of a gene from E. coli, desi gnated dxs, that encodes D-1-deoxyxylulose-5-phosphate synthase, The d xs gene was identified as part of an operon that also contains ispA, t he gene that encodes farnesyl-diphosphate synthase, D-1-Deoxyxylulose- 5-phosphate synthase belongs to a family of transketolase-like protein s that are highly conserved in evolution.