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PurF-Independent Phosphoribosyl Amine Formation in yjgF Mutants of Salmonella enterica Utilizes the Tryptophan Biosynthetic Enzyme Complex Anthranilate Synthase-Phosphoribosyltransferase

Beth Ann Browne, A. Itzel Ramos, and Diana M. Downs^*

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

Received 24 May 2006/ Accepted 24 July 2006

In Salmonella enterica, the biosynthetic pathways for the generation of purines and the essential cofactor thiamine pyrophosphate branch after sharing five enzymatic steps. Phosphoribosyl amine (PRA) is the first intermediate in the common portion of the pathway and is generated from phosphoribosylpyrophosphate and glutamine by the PurF enzyme (phosphoribosylpyrophosphate amidotransferase). A null mutation in yjgF allows PurF-independent PRA formation by an unknown mechanism. The tryptophan biosynthetic enzyme complex anthranilate synthase-phosphoribosyltransferase, composed of the TrpD and TrpE proteins, was shown to be essential for PRA formation in strains lacking both yjgF and purF. The activity generating PRA in a yjgF mutant background has features that distinguish it from the TrpDE-mediated PRA formation shown previously for this enzyme in strains with an active copy of yjgF. The data presented here are consistent with a model in which the absence of YjgF uncovers a new catalytic activity of TrpDE.

Present address: Division of Geology and Planetary Sciences, CalTech, Pasadena, CA 91125.

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