TheS subunit of RNA polymerase is the master regulator of a regulatory network that controls stationaryphase induction as well as osmotic regulation of many genes in Escherichia coli. In an attempt to identify additional regulatory components in this network, we have isolated Tn10 insertion mutations that in trans alter the expression of osmY and other S -dependent genes. One of these mutations confered glucose sensitivity and was localized in pgi (encoding phosphoglucose isomerase). pgi::Tn10 strains exhibit increased basal levels of expression of osmY and otsBA in exponentially growing cells and reduced osmotic inducibility of these genes. A similar phenotype was also observed for pgm and galU mutants, which are deficient in phosphoglucomutase and UDP-glucose pyrophosphorylase, respectively. This indicates that the observed effects on gene expression are related to the lack of UDP-glucose (or a derivative thereof), which is common to all three mutants. Mutants deficient in UDP-galactose epimerase (galE mutants) and trehalose-6-phosphate synthase (otsA mutants) do not exhibit such an effect on gene expression, and an mdoA mutant that is deficient in the first step of the synthesis of membrane-derived oligosaccharides, shows only a partial increase in the expression of osmY. We therefore propose that the cellular content of UDP-glucose serves as an internal signal that controls expression of osmY and other S -dependent genes. In addition, we demonstrate that pgi, pgm, and galU mutants contain increased levels of S during steady-state growth, indicating that UDP-glucose interferes with the expression of S itself.The S subunit of RNA polymerase in Escherichia coli is involved in the expression of a large number of genes and operons, of which more than 30 have been identified. Nearly all of these genes are induced during entry into stationary phase, and a similar regulation has also been observed for rpoS, the structural gene encoding S (recently reviewed in references 22 and 23). This control of the intracellular level of S operates at the transcriptional as well as posttranscriptional levels (34-37, 40, 42, 46) and also includes a mechanism that differentially influences the stability of S , which is a very unstable protein (with a half-life of 1.4 min) in exponentially growing cells (35).Within the large S regulon, differential regulation has been observed for subsets of genes. For instance, appCBA, hyaAB-CDEF, and appY are also anaerobically induced, and S is required for this induction (5,6,14,16). The expression of a rather large subfamiliy of S -dependent genes (e.g., otsBA, treA, osmB, osmY, and bolA) responds to changes in medium osmolarity (9,19,24,25,27,59). These regulatory responses can be observed in growing cells that contain a low level of S (18,35,54), indicating that the view of S as a stationaryphase-specific sigma factor may be too narrow. In fact, we have recently presented evidence for a posttranscriptional induction of S expression in response to high osmolarity in growing cells (35). Furth...

SummaryThe translation of rpoS, which encodes the general stress sigma factor, S , in Escherichia coli, is stimulated by various stress conditions. Regulatory factors involved in this control are the RNA-binding Hfq (HF-I) protein, the histone-like protein H-NS and the small regulatory DsrA-RNA (with the last being specifically required for increased rpoS translation at low temperature). Here, we report the characterization of a transposon insertion mutant (Tn10-8) with reduced S levels that led to the identification of an additional factor involved in the regulation of rpoS translation, the LysR-like regulator LeuO.