THE PANE GENE, ENCODING KETOPANTOATE REDUCTASE, MAPS AT 10 MINUTES AND IS ALLELIC APBA IN SALMONELLA-TYPHIMURIUM

In Salmonella typhimurium, precursors to the pyrimidine moiety of thia mine are synthesized de novo by the purine biosynthetic pathway or the alternative pyrimidine biosynthetic (APB) pathway, The apbA gene was the first locus defined as required for function of the APE pathway (D . M. Downs and L. Petersen, J. Bacteriol. 176:4858-4864, 1994), Recent work showed the ApbA protein catalyzes the NADPH-specific reduction o f ketopantoic acid to pantoic acid. This activity had previously been associated with the pantothenate biosynthetic gene panE. Although prev ious reports placed panE at 87 min on the Escherichia coli chromosome, we show herein that apbA and panE are allelic and map to 10 min on bo th the S. typhimurium and E. coli chromosomes. Results presented here suggest that the role of ApbA in thiamine synthesis is indirect since in vivo labeling studies showed that pantoic acid, the product of the ApbA-catalyzed reaction, is not a direct precursor to thiamine via the APE pathway.