Transcriptional repression of gdhA in Escherichia coli is mediated by the Nac protein

Abstract

In this work we show that the nac gene from Escherichia coli is transcriptionally active, and that its expression is dependent on NRI (NtrC) and sigma-54. Northern blot experiments show a monocistronic nac-specific mRNA that is detected when wildtype cells are grown in nitrogen-limiting conditions. Our data also show that in nitrogen-limiting conditions Nac is involved in the transcriptional repression of the gdhA gene (encoding glutamate dehydrogenase) except when L-glutamine is used as the only nitrogen source. Moreover, the high level of GDH activity observed in a nac mutant strain is reduced when a wild-type nac gene is introduced under control of the lac promoter in N-limiting conditions, but not in L-glutamine or N-excess. These results suggest the existence of an additional mechanism responsible for overcoming repression by Nac. z 1998 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.

Metabolic regulation of Escherichia coli and its glnG and zwf mutants under nitrogen limitation

“…Moreover, NR I -P will activate transcription of nac which codes for Nac (the nitrogen assimilation control protein) under N-limitation. Nac represses gdhA expression in E. coli, where GDH regulation by this gene is less understood [27][28][29]. The present study implies that the down-regulation of gdhA may be partly caused by the up-regulation of nac gene expression (P < 0.05) as shown in Fig.…”

“…The present study implies that the down-regulation of gdhA may be partly caused by the up-regulation of nac gene expression (P < 0.05) as shown in Fig. 2 [27,29]. The regulation mechanism may be illustrated as given in Fig.…”

Integration of regulatory signals through involvement of multiple global regulators: control of the Escherichia coli gltBDF operon by Lrp, IHF, Crp, and ArgR

“…One would expect GdhA levels to parallel those of [NH 4 + ], while GlnA and GltBD levels would perhaps follow the inverse of [NH 4 + ] and parallel those of ATP. In fact, gdhA is repressed by Nac, with repression relieved in high [NH 4 + ], while neither gln A nor gltBD appear to respond substantially to Nac [17,44,45]. Similarly, transcription of both glnA and gltBD is repressed by Crp-cAMP while effects on gdhA are unclear (this work, [34,46]).…”

Transcriptome Analysis of Pseudomonas putida in Response to Nitrogen Availability

“…However, at low ammonium concentrations the reaction may proceed in the opposite direction, while ammonium is incorporated through the glutamine synthetase-glutamate synthase pathway (23). Strong repression of gdhA has been reported for Klebsiella pneumoniae and E. coli, which is exerted by Nac (3,25). Interestingly, up to three potential NtrC binding sites have been found upstream of gdhA, further supporting the notion that NtrC may directly exert the regulatory control corresponding to that of Nac in E. coli, even when this control is negative.…”