H-NS: a modulator of environmentally regulated gene expression.
H-NS is a small chromatin-associated protein found in enterobacteria. H-NS has affinity for all types of nucleic acids but binds preferentially to intrinsically curved DNA. The major role of H-NS is to modulate the expression of a large number of genes, mostly by negatively affecting transcription. Many of the H-NS-modulated genes are regulated by environmental signals, and expression of most of these genes is positively regulated by specific transcription factors. Therefore one of the purposes of H-NS could be to repress expression of some genes under conditions characteristic of a non-intestinal environment, but allow expression of specific genes in response to certain stimuli in the intestinal environment. The hns gene is autoregulated. In vivo the H-NS to DNA ratio is fairly constant except during cold shock, when it increases three- to fourfold. In this review we propose that only the preferential binding to intrinsically curved DNA plays a role under normal growth conditions, and we discuss the different mechanisms by which H-NS might affect gene expression and how H-NS could be involved in the response to different stress situations. Finally, we summarize the evolutionary and functional relationship between H-NS and the homologous StpA.
Atlung
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Department of Chemistry and Life Sciences, Roskilde University, Denmark. atlung@virgil.ruc.dk
Ingmer
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D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D003080:Cold Temperature; D004247:DNA / Q000378:metabolism; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D006706:Homeostasis; D018832:Molecular Chaperones; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism; D012808:Sigma Factor / Q000235:genetics; D013696:Temperature; D015534:Trans-Activators / Q000037:antagonists & inhibitors; D014882:Water-Electrolyte Balance
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C031908:H-NS protein, bacteria; D018832:Molecular Chaperones; D009687:Nuclear Proteins; D012808:Sigma Factor; C090104:StpA protein, E coli; D015534:Trans-Activators; C069567:sigma factor KatF protein, Bacteria; D004247:DNA