CHARACTERIZATION OF THE OSMOTICALLY INDUCIBLE GENE OSME OF ESCHERICHIA-COLI K-12

osmE, an osmotically inducible gene of Escherichia coli, was physicall y mapped on the bacterial chromosome, cloned and sequenced. osmE appea red to encode a 12021Da protein of unknown function, with a lipoprotei n-type signal sequence at the amino-terminus. The osmE reading frame w as confirmed by sequencing the junction of an osmE-phoA gene fusion. o smE was demonstrated to be transcribed as a single cistron. A Phi[osmE (p)-lac] operon fusion was constructed, and analysis of its expression demonstrated that osmE osmotic regulation probably occurs at the tran scriptional level. The osmE promoter was identified by both S1 nucleas e and primer extension mapping of the 5' end of the osmE mRNA, by dele tion analysis and by identification of a point mutation reducing its a ctivity. Sequence information sufficient for expression and osmotic re gulation is present on a DNA fragment extending from positions -37 to + 52 with respect to the osmE transcription start. Uninduced expressio n of the osmE-lac fusion was increased in the presence of mutations in the hns and himA genes. The osmE promoter overlaps a promoter for a g ene transcribed in the opposite direction, efg. Transcription from the efg promoter is only weakly affected by osmotic pressure and is indep endent of the presence of an intact OsmE protein.