FnrS | |
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![]() Conserved secondary structure of FnrS RNA. The colour of nucleotides indicate their conservation within the family. | |
Identifiers | |
Symbol | FnrS |
Rfam | RF01796 |
Other data | |
RNA type | Gene |
Domain(s) | Enterobacteriaceae |
PDB structures | PDBe |
FnrS RNA is a family of Hfq-binding small RNA whose expression is upregulated in response to anaerobic conditions. It is named FnrS because its expression is strongly dependent on fumarate and nitrate reductase regulator (FNR), a direct oxygen availability sensor.[1][2]
A conserved intergenic region between genes ydaN and dbpA was predicted to encode an sRNA, adjacent to where another non-coding RNA (C0343) has been identified.[3] However, northern blot analysis of this 477bp sequence yielded no results.[4] A subsequent tiling array analysis sequencing Hfq-binding sRNA found that the Watson strand did indeed encode an sRNA.[1]
FnrS has been shown to downregulate 32 different mRNAs in Enterobacteria, in 15 of these cases it does so by base-pairing with the mRNA transcript.[1] The majority of genes downregulated by FnrS are required for aerobic metabolism or the oxidative stress response.[2] Some of the genes downregulated by FnrS are:[1]
A study incorporating comparative target prediction and subsequent experimental verification of selected predictions, suggests that FnrS might be a more global regulator in Escherichia coli. It is predicted to control several transcription factors. These include the verified targets marA and IscR.[9] MarA activates genes involved in the resistance to superoxide,[10] which might not be necessary at the anaerobic conditions where FnrS is expressed. IscR regulates genes for iron-sulfur-cluster containing or biogenesis proteins.[11] FnrS might be involved in the observed O2 dependent expression of the IscR regulon.[11] Further targets of FnrS are nagZ and sdhA.[9]
There is also evidence to suggest that the expression of FnrS is regulated by the RcsCDB signalling system in Salmonella enterica.[12]