Regulation of Nitrogen Assimilation

  • Boris Magasanik


The preferred single nitrogen source for Escherichia coli and other enteric bacteria is ammonia, in at least 1 mM concentration. Although a number of other nitrogen containing compounds for example arginine, proline, glutamine, glutamate and aspartate in the case of E. coli, and in addition dinitrogen, nitrate, histidine and urea in the case of Klebsiella pneumoniae can be used, none support a growth rate as fast as that attained when ammonia serves as the source of nitrogen. The expression of genes subject to nitrogen regulation (Ntr) can be activated during growth on any one of these growth rate limiting sources of nitrogen. In the case of some of these Ntr genes or operons, nitrogen limitation is sufficient to elicit the response. Other operons, such as those comprising the genes for the degradation of histidine and proline are in addition subject to repression which is overcome by the addition of the particular nitrogen source to the medium. Thus in these cases, both the presence of the inducer and nitrogen limitation are required for the response (reviewed in Magasanik).1


Glutamine Synthetase Nitrogen Assimilation Open Complex Transcriptional Enhancer Integration Host Factor 
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© R.G. Landes Company 1996

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  • Boris Magasanik

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