Isolation of the rpoD gene encoding the principal sigma factor of the deep-sea piezophilic bacterium Shewanella violacea strain DSS12 and its overexpression in Escherichia coli

The gene encoding the principal a factor (rpoD) of the piezophilic bacteriu m Shewanella violacea was cloned and sequenced. The rpoD gene was found to encode a polypeptide consisting of 614 amino acid residues, showing 75.6 an d 64.3% identity to those of Escherichia coli and Pseudomonas putida, respe ctively, Comparison with E, coli sigma (70) and P. putida sigma (70) showed that significant similarity exists in four conserved regions known to be r equired for promoter recognition and core binding. Using an expression plas mid harboring the rpoD gene, the S, violacea sigma (70) factor was overexpr essed in E, coli and successfully purified to near homogeneity.