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 chromo some and its activity measured during the growth cycle. Logarithmicall y growing cultures had low levels of Phi(hmp-lacZ) expression, which i ncreased 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 r poS encoding the stationary phase-specific sigma subunit of RNA polyme rase sigma(S). A himA mutation resulted in a 1.5-fold increase in expr ession of Phi(hmp-lacZ), but did not affect growth phase-dependent reg ulation. A single transcriptional start site was found for hmp, locate d 38 bp upstream of the initiation codon. Putative Fnr boxes at positi ons -2 to +11 occur in the hmp promoter region.