Many of the changes in gene expression observed when Escherichia coli cells enter stationary phase are regulated at the level of transcription initiation. A group of stationary-phase-inducible promoters, known as "gearbox" promoter, display a characteristic sequence in the -10 region which differs greatly from the consensus sequence for sigma 70-dependent promoters. Here we describe our studies on the gearbox promoters bolAp1 and mcbAp, responsible for the temporally regulated transcription of bolA and the genes involved in the synthesis of the peptide antibiotic microcin B17, respectively. Deletion analysis of mcbAp demonstrated that the stationary-phase-inducible properties of this promoter are found in a DNA fragment extending from -54 to +11 bp, surrounding the transcriptional start site, and are separable from DNA sequences responsible for the OmpR-dependent stimulation of transcription of mcbAp. In vitro transcription studies indicate that the RNA polymerase holoenzyme involved in the transcription of mcbAp contains sigma 70. In this and an accompanying paper (R. Lange and R. Hengge-Aronis, J. Bacteriol. 173: 4474-4481, 1991), experiments are described which show that the product of katF, a global regulator of stationary-phase gene expression and a putative sigma factor, is required for the expression of bolAp1 fused to the reporter gene lacZ. In contrast, mcbAp appears to be negatively regulated by katF. We discuss the implications of these results for postexponential gene expression and the role of gearbox sequences in the regulation of promoter activity.

Nitrogen source regulation of glutamate synthase activity in Bacillus subtilis occurs at the level of transcription of the gitA and gltB genes, which encode the two subunits of the enzyme. We show here that transcription of gltA requires the product of gltC, a gene whose transcription is divergent from that of g1tA and whose transcriptional control sequences overlap those of g1tA. gltC mutants had decreased, aberrantly regulated levels of glutamate synthase activity and decreased g1tA mRNA. The gltC gene product could act in trans to complement both these defects. In addition, the gliC gene product repressed its own transcription. The DNA sequence of gltC revealed that-its putative product is very similar to a number of positive regulatory proteins from gram-negative bacteria (the LysR family).Glutamate synthase (glutamine:2-oxoglutarate amidotransferase; GOGAT) is a key enzyme of nitrogen metabolism in Bacillus subtilis. It catalyzes the synthesis of glutamate and, together with glutamine synthetase, is responsible for the sole pathway for assimilation of ammonium into organic compounds. GOGAT activity is regulated by the available nitrogen source; it is high in cells grown with ammonia as the nitrogen source and low in cells grown with glutamate as the nitrogen source (30, 37). We and others have shown previously (4, 31) that these variations in enzyme activity are due to changes in the rate of synthesis and steady-state levels of transcripts of gitA and gltB, the genes that code for the large and small subunits of GOGAT, respectively (14). We show here that the product of a third gene, gltC, is required for expression from the gitA promoter. We postulate that the product of gItC is a positive transcription factor that acts at the gitA promoter to stimulate transcription under conditions of limiting glutamate.The detailed mechanism by which the genes for glutamate synthase are regulated is not known for any species. While global control of nitrogen metabolism (ntr system; see reference 22 for a review) has been well described for enteric organisms, this system does not appear to be involved directly in the regulation of GOGAT gene expression in Escherichia coli. GOGAT levels in E. coli are repressed by growth in glutamate, but, in contrast to the situation in B. subtilis, are equally derepressed by growth in ammonia or glutamine (7). GOGAT levels in Salmonella typhimurium are regulated in a complex, poorly understood manner by a growth rate-limiting nitrogen source (6). In S. typhimurium, the large and small subunits of GOGAT are encoded by gltB and gltD, respectively; these two genes are apparently cotranscribed (21). The genes encoding the subunits of E. coli GOGAT, also called gltB and gltD, have been cloned (13) and recently sequenced (28). A third gene, gltF, downstream from and possibly cotranscribed with gltB and gltD, does not appear to be involved in GOGAT regulation, but rather in ntr regulation (7). gltF mutants are unable to fully derepress genes which respond to glnF (ntrA) and glnG (ntrC) under c...

Synthesis of glutamate, the cell's major donor of nitrogen groups and principal anion, occupies a significant fraction of bacterial metabolism. In Bacillus subtilis, the gltAB operon, encoding glutamate synthase, requires a specific positive regulator, GltC, for its expression. In addition, the gltAB operon was shown to be repressed by TnrA, a regulator of several other genes of nitrogen metabolism and active under conditions of ammonium (nitrogen) limitation. TnrA was found to bind directly to a site immediately downstream of the gltAB promoter. As is true for other genes, the activity of TnrA at the gltAB promoter was antagonized by glutamine synthetase under certain growth conditions.

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Volcanic ash was collected from the Moses Lake region of Washington State after the 18 May 1980 eruption of Mt. St. Helens. The ash was tested in a short-term bioassay system using hamsters exposed by intratracheal instillation. One day after exposure the lungs were lavaged and the fluid collected was characterized using several parameters that represent different manifestations of lung injury: (a) in situ phagocytic ability of pulmonary macrophages; (b) the inflammatory response, as shown by polymorphonuclear neutrophil numbers and albumin levels in lung lavage fluid; and (c) release of cytoplasmic and lysosomal enzymes into the cell-free supernatant of lung-lavage fluid. The response to volcanic ash was elevated compared to controls, but was similar to the response to Al2O3, a dust considered to be relatively inert. In contrast, the response to alpha-quartz, a highly toxic fibrogenic dust, was significantly greater than the response to either volcanic ash or Al2O3 for most parameters measured.