Cloning and characterization of Planctomyces limnophilus rpoN:: complementation of a Salmonella typhimurium rpoN mutant strain

The rpoN gene, which encodes the alternative sigma factor sigma(54), was cloned from the budding, peptidoglycan-less bacterium Planctomyces limnophilus. P. limnophilus rpoN complemented the Ntr(-) phenotype of a Salmonella typhimurium rpoN mutant strain. The P. limnophilus rpoN gene encoded a predicted polypeptide that was 495 residues in length and shared a significant homology with ether members of the sigma(54) family. The protein sequence displayed all of the characteristic motifs found in members of this family, including the C-terminal helix-turn-helix motif and the well-conserved RpoN box. A potential sigma(54)-dependent activator was also identified in P. limnophilus. These findings extend the range of phylogenetic groups within the Domain Bacteria that are known to contain sigma(54). (C) 1998 Elsevier Science B.V. All rights reserved.