Mutagenesis of the downstream region of the Escherichia coli hns promoter

The promoter of hns, the structural gene for the abundant nucleoid-associat ed protein H-NS of Escherichia coli, contains, downstream of the initiation site, two four bp-long 'CG clamps', one of which overlaps the potential ta rget sequence (CCAAT) of CspA, the cold-shock transcriptional enhancer of t his gene. To establish the role of these potential regulatory signals durin g the cold-shock activation of hns, the CCCCAAT sequence has been subjected to mutagenesis, weakening the strength of the CG clamp and scrambling or i nverting the CCAAT sequence. The resulting mutated hns promoters were place d in front of a reporter gene (cat) and their activity was studied in cells subjected to cold-shock under conditions where the increase in the concent ration of CspA is either large or small. Our results allow us to conclude t hat although not essential, the CCCCAAT sequence, mainly due to the presenc e of the CG clamp, may play an important role in the CspA-mediated regulati on of hns expression at both transcriptional and translational levels. (C) 2001 Societe francaise de biochimie et biologie moleculaire / Editions scie ntifiques et medicales Elsevier SAS.