Glutamine synthetase gene expression at elevated hydrostatic pressure in a deep-sea piezophilic Shewanella violacea

A glutamine synthetase gene ( glnA ) was isolated from a deep-sea piezophilic bacterium, Shewanella violacea strain DSS12. A 7.5-kb Sac I fragment containing the complete glnA gene was cloned and sequenced. The glnA gene was found to encode a protein consisting of 469 amino acid residues, showing 75.0% identity to the glutamine synthetase of Escherichia coli . Primer extension analyses revealed two transcription initiation sites in glnA and expression from each site was positively regulated by pressure. Putative promoters recognized by σ 70 and σ 54 were identified in the region upstream of glnA . An electrophoretic mobility shift assay demonstrated that S. violacea σ 54 specifically binds to the promoter region of glnA , suggesting that σ 54 may play an important role in pressure-regulated transcription in this piezophilic bacterium.