[1] 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] 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.