rpoN

The gene rpoN (RNA polymerase, nitrogen-limitation N) encodes the sigma factor sigma-54 (σ54, sigma N, or RpoN), a protein in Escherichia coli and other species of bacteria. RpoN antagonizes RpoS sigma factors.^[1]

Biological role

Originally identified as a regulator of genes involved in nitrogen metabolism and assimilation under nitrogen limiting conditions,^[2] E. coli σ54 has since been shown to play important regulatory roles in a variety of other cellular processes. Similarly, σ54 homologues in other species regulate a wide range of processes, including flagellar synthesis and virulence.^[3]

Sequence specificity and mechanism of action

σ54 promoter elements consist of conserved nucleotides located at -12 and -24 with respect to the transcription start site.^[4] This contrasts with members of the σ70 family, which recognize conserved promoter elements located at roughly -10 and -35 with respect to the transcription start site.^[5] Unlike the members of the σ70 family, σ54 proteins have been shown to bind promoter DNA independent of core RNAPin vitro.^[6] Another distinguishing characteristic of σ54 proteins is their absolute requirement for activator proteins, known as bacterial enhancer binding proteins (bEBPs), to initiate transcription.^[4][7] Thus, both active and inactive forms of RNAP:σ54 are bound at promoters.^[8]

The RpoN-regulated promoter elements have the consensus sequence as follows: TTGGCACGGTTTTTGCT.^[9]

References