Biology Reference
In-Depth Information
RT-PCR assays confirm the influence of FurA on
furB
transcription that
clearly decreases in the FurA overexpressing mutant (
González et al., 2010
).
The influence of several nutritional and environmental factors on
furB
and
furC
expression was investigated by RT-PCR and using GFP constructs
driven by their promoters (
López-Gomollón et al., 2009
). Among the
conditions tested, neither osmotic stress induced by sucrose nor salt stress
affected by FurB or FurC expression. However, oxidative challenge induced
by H
2
O
2
enhanced the expression of both genes.
Similar to FurA, FurB exhibits the CP haeme-regulatory motif, and
binding to this cofactor impairs its interaction with DNA. In vitro assays
show that FurB binds to its own promoter (
Hernández, López-Gomollón
et al., 2004
). This interaction is stronger in the absence of divalent metals
and it is destroyed in the presence of Zn
2+
. Reducing conditions managed
by the presence of DTT positively affected FurB-DNA interaction. Further
work involving in vivo studies should be done in order to address the role
of Zn
2+
in FurB autoregulation.
3.1.5. Metabolic and regulatory networks involving Fur proteins
Among the
fur
paralogues identified in cyanobacteria,
furA
and their ortho-
logues seem to be the most important for the cell since all attempts to
fully inactivate the
furA
genes from cyanobacteria have been unsuccessful
under standard growth conditions (
Ghassemian & Straus, 1996
;
Hernández,
Muro-Pastor et al., 2006
;
Kunert et al., 2003
;
Michel, Pistorius, & Golden,
2001
). Therefore, it is not surprising that FurA seems to be involved directly
or indirectly in the modulation of genes participating in several metabolic
pathways, including nitrogen metabolism, transcription, photosynthesis and
respiration and, of course, iron uptake and oxidative stress, among others.
3.1.5.1. Iron homeostasis and the oxidative stress response
Cyanobacterial iron homeostasis is mainly maintained by FurA ortho-
logues (
Ghassemian & Straus, 1996
; González et al., 2010;
Houot et al.,
2007
;
Kunert et al., 2003
;
Straus, 1994
). The close relationship between iron
homeostasis and oxidative stress has been extensively investigated (
Cornelis,
Wei, Andrews, & Vinckx, 2011
;
Faulkner & Helmann, 2011
;
Latifi et al.,
2005
;
Latifi, Ruiz, & Zhang, 2009
;
Shcolnick, Summerfield, Reytman,
Sherman, & Keren, 2009
). This connection is even tighter in cyanobacteria,
whose need for iron is about 10 times greater than that of heterotrophic
bacteria, and whose photosynthetic and respiratory electron transport chains
are particularly sensitive to spare ROS generated by the Mehler reaction
