An overlap between osmotic and anaerobic stress responses: a potential role for DNA supercoiling in the coordinate regulation of gene expression

Abstract

The regulation of several genes in response to osmotic and anaerobic stress has been examined. We have demonstrated a clear overlap between these two regulatory signals. Thus, the osmotically induced proU and ompC genes require anaerobic growth for optimum induction while the anaerobically induced tppB gene is also regulated by osmolarity. Furthermore, normal expression of tppB and ompC requires the positive regulatory protein OmpR, yet this requirement can be partially, or even fully, overcome by altering the growth conditions. Finally, the pleiotropic, anaerobic regulatory locus, oxrC, is also shown to affect expression of the osmotically regulated proU gene. The oxrC mutation is shown to affect the level of negative supercoiling of plasmid DNA and its effects on gene expression can be explained as secondary consequences of altered DNA topology. We suggest that there is a class of 'stress-regulated' genes that are regulated by a common mechanism in response to different environmental signals. Furthermore, our data are consistent with the notion that this regulatory overlap is mediated by changes in DNA supercoiling in response to these environmental stresses.

The torR gene of Escherichia coli encodes a response regulator protein involved in the expression of the trimethylamine N-oxide reductase genes

“…This regulator could be either an aerobic repressor which competes with TorR for the binding sites or an anaerobic activator which associates with TorR to allow torA transcription (8). Alternatively, the effect of aerobiosis could be explained as a secondary consequence of changes in DNA topology (20) …”

Cloning, sequence and mutagenesis of the structural gene of Pseudomonas aeruginosa CysB, which can activate algD transcription

“…It is well established that environmental signals (e.g. osmolarity, nutrient status, temperature) can alter DNA supercoiling in vivo, and that changes in DNA topology play a role, at least in part, in the regulation of gene expression (Ni Bhriain et al, 1989). DNA supercoiling has been shown to regulate gene expression in a number of systems, including virulence in Shigella flexneri (Dorman et al, 1990;Dorman, 1995).…”

The Escherichia coli phage‐shock‐protein (psp) operon

“…In vitro, psp transcription from a supercoiled template is much less dependent on IHF and on the presence of the UASs than is transcription from a linear template (our unpublished results). Since osmotic shock affects DNA topology (Higgins et al, 1988;Ni Bhriain et al, 1989), increased negative supercoiling may substitute for the IHF and UAS requirement in the psp intergenic region. Figure 1 shows that there are three ( 70 ) promoters for pspF (Jovanovic et al, 1996).…”