Nac‐mediated repression of the serA promoter of Escherichia coli
Open Access
- 18 July 2002
- journal article
- research article
- Published by Wiley in Molecular Microbiology
- Vol. 45 (2), 351-363
- https://doi.org/10.1046/j.1365-2958.2002.02994.x
Abstract
Escherichia coli and related bacteria contain two paralogous PII‐like proteins involved in nitrogen regulation, the glnB product, PII, and the glnK product, GlnK. Previous studies have shown that cells lacking both PII and GlnK have a severe growth defect on minimal media, resulting from elevated expression of the Ntr regulon. Here, we show that this growth defect is caused by activity of the nac product, Nac, a LysR‐type transcription factor that is part of the Ntr regulon. Cells with elevated Ntr expression that also contain a null mutation in nac displayed growth rates on minimal medium similar to the wild type. When expressed from high‐copy plasmids, Nac imparts a growth defect to wild‐type cells in an expression level‐dependent manner. Neither expression of Nac nor lack thereof significantly affected Ntr gene expression, suggesting that the activity of Nac at one or more promoters outside the Ntr regulon was responsible for its effects. The growth defect of cells lacking both PII and GlnK was also eliminated upon supplementation of minimal medium with serine or glycine for solid medium or with serine or glycine and glutamine for liquid medium. These observations suggest that high Nac expression results in a reduction in serine biosynthesis. β‐Galactosidase activity expressed from a Mu d1 insertion in serA was reduced approximately 10‐fold in cells with high Nac expression. We hypothesize that one role of Nac is to limit serine biosynthesis as part of a cellular mechanism to reduce metabolism in a co‐ordinated manner when cells become starved for nitrogen.Keywords
This publication has 30 references indexed in Scilit:
- Nitrogen regulatory protein C-controlled genes of Escherichia coli : Scavenging as a defense against nitrogen limitationProceedings of the National Academy of Sciences, 2000
- Studies on the roles of GlnK and GlnB in regulatingKlebsiella pneumoniaeNifL-dependent nitrogen controlFEMS Microbiology Letters, 1999
- Transcriptional repression ofgdhAinEscherichia coliis mediated by the Nac proteinFEMS Microbiology Letters, 1998
- An alternative PII protein in the regulation of glutamine synthetase in Escherichia coliMolecular Microbiology, 1996
- Salmonella typhimuriumApparently Perceives External Nitrogen Limitation as Internal Glutamine LimitationJournal of Molecular Biology, 1996
- Cloning and organization of the abc and mdl genes of Escherichia coli: relationship to eukaryotic multidrug resistanceGene, 1993
- The role of the NAC protein in the nitrogen regulation of Klebsiella aerogenesMolecular Microbiology, 1991
- Improved single and multicopy lac-based cloning vectors for protein and operon fusionsGene, 1987
- Physical and genetic characterization of the glnA--glnG region of the Escherichia coli chromosome.Proceedings of the National Academy of Sciences, 1981
- The relation of serine-glycine metabolism to the formation of single-carbon unitsBiochimica et Biophysica Acta, 1963