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Journal of Bacteriology, February 2008, p. 815-822, Vol. 190, No. 3
0021-9193/08/$08.00+0     doi:10.1128/JB.00582-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Mutations in the Tryptophan Operon Allow PurF-Independent Thiamine Synthesis by Altering Flux In Vivo{triangledown}

Itzel Ramos,{dagger} E. I. Vivas, and D. M. Downs*

Department of Bacteriology, University of Wisconsin—Madison, Madison, Wisconsin 53706

Received 16 April 2007/ Accepted 1 June 2007

Phosphoribosyl amine (PRA) is an intermediate in purine biosynthesis and also required for thiamine biosynthesis in Salmonella enterica. PRA is normally synthesized by phosphoribosyl pyrophosphate amidotransferase, a high-turnover enzyme of the purine biosynthetic pathway encoded by purF. However, PurF-independent PRA synthesis has been observed in strains having different genetic backgrounds and growing under diverse conditions. Genetic analysis has shown that the anthranilate synthase-phosphoribosyltransferase (AS-PRT) enzyme complex, involved in the synthesis of tryptophan, can play a role in the synthesis of PRA. This work describes the in vitro synthesis of PRA in the presence of the purified components of the AS-PRT complex. Results from in vitro assays and in vivo studies indicate that the cellular accumulation of phosphoribosyl anthranilate can result in nonenzymatic PRA formation sufficient for thiamine synthesis. These studies have uncovered a mechanism used by cells to redistribute metabolites to ensure thiamine synthesis and may define a general paradigm of metabolic robustness.

* Corresponding author. Mailing address: Department of Bacteriology, University of Wisconsin—Madison, 420 Henry Mall, Madison, WI 53706. Phone: (608) 265-4630. Fax: (608) 262-9865. E-mail: downs{at}bact.wisc.edu

{triangledown} Published ahead of print on 8 June 2007.

{dagger} Present address: Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139.

Journal of Bacteriology, February 2008, p. 815-822, Vol. 190, No. 3
0021-9193/08/$08.00+0     doi:10.1128/JB.00582-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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