Roles of RpoS (sigma(s)), IHF and ppGpp in the expression of the hmp gene encoding the flavohemoglobin (Hmp) of Escherichia coli K-12

The Escherichia coli K-12 gene hmp encodes the flavohemoglobin Hmp. A hmp promoter Phi(hmp-lacZ)-operon fusion was constructed in the chromosome and its activity measured during the growth cycle. Logarithmically growing cultures had low levels of Phi(hmp-lacZ) expression, which increased two-fold at the onset of stationary phase in rich medium. The effect was abolished in a strain carrying a null allele of the gene rpoS encoding the stationary phase-specific sigma subunit of RNA polymerase sigma(S). A himA mutation resulted in a 1.5-fold increase in expression of Phi(hmp-lacZ), but did not affect growth phase-dependent regulation. A single transcriptional start site was found for hmp, located 38 bp upstream of the initiation codon. Putative Fnr boxes at positions -2 to +11 occur in the hmp promoter region.