The gene rpoN (RNA polymerase, nitrogen-limitation N) encodes the sigma factor sigma-54 (?54, sigma N, or RpoN), a protein in Escherichia coli and other species of bacteria. RpoN antagonizes RpoS sigma factors.
Video RpoN
Biological role
Originally identified as a regulator of genes involved in nitrogen metabolism and assimilation under nitrogen limiting conditions, E. coli ?54 has since been shown to play important regulatory roles in a variety of other cellular processes. Similarly, ?54 homologues in other species regulate a wide range of processes, including flagellar synthesis and virulence.
Maps RpoN
Sequence specificity and mechanism of action
?54 promoter elements consist of conserved nucleotides located at -12 and -24 with respect to the transcription start site. This contrasts with members of the ?70 family, which recognize conserved promoter elements located at roughly -10 and -35 with respect to the transcription start site. Unlike the members of the ?70 family, ?54 proteins have been shown to bind promoter DNA independent of core RNAPin vitro. Another distinguishing characteristic of ?54 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:?54 are bound at promoters.
The RpoN-regulated promoter elements have the consensus sequence as follows: TTGGCACGGTTTTTGCT.
References
Source of the article : Wikipedia
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