RyhB RNA levels are inversely correlated with mRNA levels for the
sdhCDAB operon, encoding
succinate dehydrogenase, as well as five other genes previously shown to be positively regulated by Fur by an unknown mechanism. These include two other genes encoding enzymes in the
tricarboxylic acid cycle,
acnA and
fumA, two
ferritin genes,
ftnA and
bfr, and a gene for
superoxide dismutase,
sodB. A number of other genes have been predicted computationally and verified as targets by
microarray analysis:
napF,
sodA,
cysE,
yciS,
acpS,
nagZ and
dadA. RyhB is bound by the
Hfq protein, that increases its interaction with its target messages. A
comparative genomics target prediction approach suggests that the mRNAs of eleven additional iron containing proteins are controlled by RyhB in
Escherichia coli. Two of those (
erpA,
nirB) and two additional targets that are not directly related to iron (
nagZ,
marA) were verified with a GFP reporter system. It has been shown that RyhB has a role in targeting the polycistronic transcript iscRSUA for differential degradation. RyhB binds to the second
cistron of iscRSUA, which encodes machinery for biosynthesis of Fe-S clusters. This binding promotes cleavage of the downstream iscSUA transcript. This cleavage leaves the 5′ IscR transcript which is a transcriptional regulator responsible regulating several genes that depend on cellular Fe-S level. More recent data indicate a potential dual function role for RyhB. In this capacity it may act both as an RNA-RNA interaction based regulator and as a transcript encoding for a small protein. RyhB is
analogous to
PrrF RNA found in
Pseudomonas aeruginosa, to
HrrF RNA in
Haemophilus species and to IsaR1 in
cyanobacteria. First sRNA shown to mediate persistence to antibiotics in
E.coli. The finding may lead to discovery of novel treatments for persistent infections. ==Naming==