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The alarmone ppGpp is an important signal molecule for the stringent response. Escherichia coli relA encodes a ppGpp synthetase, and although the regulation of RelA protein activity has been studied extensively, the regulation of relA transcription remains unclear. Here, we describe a novel relA promoter, relA P2. According to quantitative measurement of mRNA by primer extension analysis, the previously reported promoter relA P1 is constitutively active throughout growth, while relA P2 is induced temporarily at the transition state between the exponential growth and stationary phases. A chromosomal transcriptional lacZ fusion ( relA P2-lacZ ) showed that relA P2 is positively regulated by H-NS and CRP. Furthermore, the reduced activity of relA P2-lacZ in an hns mutant could be rescued by an rpoS mutation, which is sufficient to derepress the relA P2-lacZ activity. These data suggest that transient expression from the relA P2 promoter is controlled by several global regulators. This may account for the complex regulation of relA expression in Escherichia coli .

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