The general stress response of is triggered by a variety of environmental and metabolic stresses which activate the σ transcription factor. Among the more than 100 genes controlled by σ (the genes), the functions identified thus far include resistance to oxidative stress, resistance to protein denaturation and resistance to osmotic stress. To understand the breadth of functions in which genes participate, the transcriptional organization and predicted products of two such genes previously identified in a screen for σ-dependent fusions were analysed. The ::Tn and ::Tn fusions are unusual among genes in that their expression appears to be completely dependent upon σ. By plasmid-integration experiments, fusion analyses and site-directed mutagenesis, stress-inducible, σ-dependent promoters for both these fusions were identified. The fusion marked an ORF ( or ) which by sequence analysis lay in a monocistronic transcriptional unit. This ORF encoded a predicted 461-residue product which had high identity with Class I sugar transporters of the major facilitator superfamily. It was speculated that the product could serve either a nutritional or an osmotic protection function. In contrast, the fusion identified an ORF ( or ) which appeared to be the second gene of a two-gene operon. This ORF encoded a predicted 62-residue product which resembled a small protein of unknown function. The σ-dependent promoter lay immediately upstream from and appeared to be an internal promoter for the operon.


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