Biology Reference
In-Depth Information
The identification of an antisense RNA that covers the complete
furA
gene and is cotranscribed with the cell wall-binding protein Alr1690 adds
another mechanism for dynamic, fine-tuning
furA
regulation at the post-
transcriptional stage (
Hernández, Muro-Pastor et al., 2006
). Insertional
inactivation of the
alr1690-
α
-furA
dicistronic message produces smaller cells
exhibiting a 2.5-fold increase in FurA expression and 62% of iron con-
tent with respect to
Anabaena
WT. Δ
alr1690-
α
-furA
cells display a reduced
number of contorted thylakoids, as well as alterations in the photosynthetic
apparatus, leading to lower photosynthetic performance indexes (
Hernández
et al., 2010
). These results indicate that the expression of the
alr1690-
α
-furA
message is required for the maintenance of a proper thylakoid arrangement,
efficient regulation of iron uptake and optimal yield of the photosynthetic
machinery.
The occurrence of anti-
fur
RNAs has been found in other cyanobacte-
rial strains, namely
Microcystis aeruginosa
PCC 7806 and
Synechocystis
PCC
6803, showing rather different gene contexts between them (
Sevilla et al.,
2011
). In the case of
Microcystis
, the anti-
fur
RNA spans the whole Ma
fur
CDS and part of the flanking
dnaJ
and
sufE
sequences, while Syα-
fur
RNA
covers only part of the coding sequence of the
fur
orthologue
sll0567
. It has
been reported that in heterotrophic bacteria, Fur can indirectly activate sev-
eral genes by repressing trans-acting, small antisense RNAs, such as RyhB
in
E. coli
or the functional homologues PrrF in
Pseudomonas
and NrrF in
Neisseria
(
Metruccio et al., 2009
;
Wilderman et al., 2004
). However, α
-furA
is the first antisense RNA reported to modulate a Fur protein. The ques-
tion of whether cyanobacterial Fur proteins can also repress small nc-RNAs
will require further work addressing functional transcriptomics of the many
encoded regulatory RNAs found in cyanobacteria (
Georg & Hess, 2011
).
At the post-translational level, the DNA-binding ability of FurA is
enhanced by the presence of FurC in contrast to the inhibition observed
when FurA is complexed with haeme (
Hernández, López-Gomollón et al.,
2004
;
Hernández, Peleato et al 2004
). The estimated K
d
= 0.4 ± 0.1 µM
for the FurA-haeme interaction strongly suggests that the binding takes
place in vivo as a regulatory mechanism, likely acting as a haeme-sensor
protein (
Pellicer et al., 2012
). In summary, the regulatory model for FurA
from
Anabaena
can be presented as a complex balance of several signals that
influence the final concentration of this protein along the three steps of the
genetic flow of information.
Concerning other FurA paralogues, in vitro assays indicate that FurB and
FurC might be regulated by FurA since the latter binds to their promoters.
