Nucleoid proteins stimulate stringently controlled bacterial promoters: A link between the cAMP-CRP and the (p)ppGpp regulons in Escherichia coli

We report that the H-NS nucleoid protein plays a positive role in the expre ssion of stringently regulated genes in Escherichia coli. Bacteria lacking both H-NS and the paralog StpA show reduced growth rate. Colonies displayin g an increased growth rate were isolated, and mapping of a suppressor mutat ion revealed a base pair substitution in the spoT gene. The spoT(A404E) mut ant showed low ppGpp synthesizing ability. The crp gene, which encodes the global regulator CRP, was subject to negative stringent regulation. The sta ble RNA/protein ratio in an hns, stpA strain was decreased, whereas it was restored in the suppressor strain. Our findings provide evidence of a direc t link between the cAMP-CRP modulon and the stringent response.