PrrF RNA is a small non-coding RNA

Non-coding RNA

A non-coding RNA is a functional RNA molecule that is not translated into a protein. Less-frequently used synonyms are non-protein-coding RNA , non-messenger RNA and functional RNA . The term small RNA is often used for short bacterial ncRNAs...

 involved in iron homeostasis and is found exclusively in Pseudomonas

Pseudomonas

Pseudomonas is a genus of gammaproteobacteria, belonging to the family Pseudomonadaceae containing 191 validly described species.Recently, 16S rRNA sequence analysis has redefined the taxonomy of many bacterial species. As a result, the genus Pseudomonas includes strains formerly classified in the...

species. PrrF sequences are the analogs

Analogy (biology)

An analogy is a trait or an organ that appears similar in two unrelated organisms. The cladistic term for the same phenomenon is homoplasy, from Greek for same form. Biological anologies are often the result of convergent evolution....

 of the sRNA RyhB RNA

RyhB RNA

RyhB RNA is a 90 nucleotide non-coding RNA that down-regulates a set of iron-storage and iron-using proteins when iron is limiting; it is itself negatively regulated by the ferric uptake repressor protein, Fur . This ncRNA gene was independently identified in two screens, named RyhB by Wasserman et...

and are found in tandem. Their expression is induced under iron limitation by the ferric uptake regulator (Fur) and they act to negatively regulate several genes including sodB and sdh.