The gene rpoN (RNA polymerase, nitrogen-limitation N) encodes the sigma factor sigma-54 (ÃÂ54, sigma N, or RpoN), a protein in Escherichia coli and other species of bacteria. RpoN antagonizes RpoS sigma factors.
Originally identified as a regulator of genes involved in nitrogen metabolism and assimilation under nitrogen limiting conditions, E. coli ÃÂ54 has since been shown to play important regulatory roles in a variety of other cellular processes. Similarly, ÃÂ54 homologues in other species regulate a wide range of processes, including flagellar synthesis and virulence.
ÃÂ54 promoter elements consist of conserved nucleotides located at âÂÂ12 and âÂÂ24 with respect to the transcription start site. This contrasts with members of the ÃÂ70 family, which recognize conserved promoter elements located at roughly âÂÂ10 and âÂÂ35 with respect to the transcription start site. Unlike the members of the ÃÂ70 family, ÃÂ54 proteins have been shown to bind promoter DNA independent of core RNAPin vitro. Another distinguishing characteristic of ÃÂ54 proteins is their absolute requirement for activator proteins, known as bacterial enhancer binding proteins (bEBPs), to initiate transcription. Thus, both active and inactive forms of RNAP:ÃÂ54 are bound at promoters.
The RpoN-regulated promoter elements have the consensus sequence as follows: TTGGCACGGTTTTTGCT.