J. Bacteriol., Jan 1996, 327-331, Vol 178, No. 2
Copyright © 1996, American Society for Microbiology

D-histidine utilization in Salmonella typhimurium is controlled by the leucine-responsive regulatory protein (Lrp)

K Hecht, S Zhang, T Klopotowski and GF Ames
Department of Molecular and Cell Biology, University of California at Berkeley 94720, USA.

A new class of D-histidine-utilizing mutants which carry mutations in the gene encoding the leucine-responsive regulatory protein (Lrp) has been identified in Salmonella typhimurium. The lrp mutations arise as suppressors of mutations in the genes encoding the histidine permease which drastically decrease the level of histidine transport activity. However, the suppressor effect is not exerted by elevating the level of the permease. Rather, the properties of the suppressor mutants are consistent with the notion that the parent permease mutants transport D- histidine at a low level and that in the suppressor mutants D-histidine is utilized effectively through elevated levels of racemization. The enzymatic activity of D-alanine dehydrogenase (Dad) is shown to be elevated in the suppressor mutants and is a possible pathway of D- histidine utilization. The suppressor mutations are located in the helix-turn-helix region of Lrp.

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