Stationary phase expression of the arginine biosynthetic operon argCBH in Escherichia coli.
BACKGROUND
Arginine biosynthesis in Escherichia coli is elevated in response to nutrient limitation, stress or arginine restriction. Though control of the pathway in response to arginine limitation is largely modulated by the ArgR repressor, other factors may be involved in increased stationary phase and stress expression.


RESULTS
In this study, we report that expression of the argCBH operon is induced in stationary phase cultures and is reduced in strains possessing a mutation in rpoS, which encodes an alternative sigma factor. Using strains carrying defined argR, and rpoS mutations, we evaluated the relative contributions of these two regulators to the expression of argH using operon-lacZ fusions. While ArgR was the main factor responsible for modulating expression of argCBH, RpoS was also required for full expression of this biosynthetic operon at low arginine concentrations (below 60 microM L-arginine), a level at which growth of an arginine auxotroph was limited by arginine. When the argCBH operon was fully de-repressed (arginine limited), levels of expression were only one third of those observed in deltaargR mutants, indicating that the argCBH operon is partially repressed by ArgR even in the absence of arginine. In addition, argCBH expression was 30-fold higher in deltaargR mutants relative to levels found in wild type, fully-repressed strains, and this expression was independent of RpoS.


CONCLUSIONS
The results of this study indicate that both derepression and positive control by RpoS are required for full control of arginine biosynthesis in stationary phase cultures of E. coli.
Weerasinghe
Jeevaka P
JP
McMaster University, Department of Biology, Life Sciences Building, Rm, 218, 1280 Main Street West, Hamilton, ON, Canada, L8S 4K1. jeevakapramukw@hotmail.com
Dong
Tao
T
Schertzberg
Michael R
MR
Kirchhof
Mark G
MG
Sun
Yuan
Y
Schellhorn
Herb E
HE
D001120:Arginine / Q000096:biosynthesis* / Q000494:pharmacology; D001123:Argininosuccinate Lyase / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics; D015152:Blotting, Northern; D004926:Escherichia coli / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000096:biosynthesis / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects; D009154:Mutation; D009876:Operon / Q000502:physiology*; D012097:Repressor Proteins / Q000235:genetics; D012808:Sigma Factor / Q000235:genetics
C490177:ArgR protein, E coli; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D012097:Repressor Proteins; D012808:Sigma Factor; C069567:sigma factor KatF protein, Bacteria; D001120:Arginine; D001123:Argininosuccinate Lyase