Transcriptional regulation under pressure conditions by RNA polymerase σ54 factor with a two-component regulatory system in Shewanella violacea

Deep-sea bacteria have unique systems for gene and protein expression controlled by hydrostatic pressure. One of the σ factors, σ54, was found to play an important role in pressure-regulated transcription in a deep-sea piezophilic bacterium, Shewanella violacea. A glutamine synthetase gene (glnA) has been targeted as a model for the pressure-regulated promoter to investigate transcriptional regulation by the σ54 factor. Recognition sites for σ54 and σ70 factors were observed at an upstream region of the glnA, and NtrC-binding sites were also identified at the same region. Primer extension analyses revealed that the transcription initiation sites of both promoters were determined and that transcription from the σ54 site was regulated by elevated pressure. The σ54 promoter is known to be activated by a two-component signal transduction system, the NtrB–NtrC phosphorylation relay. Our results suggested that this system might be regulated by deep-sea conditions and that the gene expression controlled by the σ54 promoter was actually regulated by pressure. We propose a possible model of the molecular mechanisms for pressure-regulated transcription.