Nitrogen is an essential
element for all life, and this is no different for the bacterial cell. Numerous cellular macromolecules contain
nitrogen, including
proteins,
nucleic acids and cell wall components. In Escherichia coli and related bacteria, the
nitrogen stress (Ntr) response allows cells to rapidly sense and adapt to
nitrogen limitation by scavenging for alternative
nitrogen sources through the transcriptional activation of transport systems and catabolic and biosynthetic operons by the global transcriptional regulator NtrC.
Nitrogen-starved bacterial cells also synthesize the (
p)ppGpp effector molecules of a second global bacterial stress response - the stringent response. Recently, we showed that the transcription of relA, the gene which encodes the major (
p)ppGpp synthetase in E. coli, is activated by NtrC during
nitrogen starvation. Our results revealed that in E. coli and related bacteria, NtrC functions in combinatorial stress and serves to couple two major stress responses, the Ntr response and stringent response.