Biology Reference
In-Depth Information
in cyanobacterial FurB/Zur orthologues (
López-Gomollón, Sevilla, Bes,
Peleato, & Fillat, 2009
and
Fig. 4.2
).
3.1.1.2. DNA-binding sites
Under conditions of iron abundance, iron-bound Fur dimers bind to target
promoters in their Fur boxes, also called iron boxes. Fur-binding sequences
were originally regarded as 19-bp inverted repeats with the consensus
(GATAATGATAATCATTATC), and reinterpreted as arrays of NATA/
TAT heptamers (
Escolar, Pérez-Martín, & de Lorenzo, 1999
). Binding of
FurA from
Anabaena
to their DNA targets is enhanced in the presence
of divalent metals and reducing conditions (
Hernández, López-Gomollón
et al., 2006
). Moreover, cyanobacterial FurA binds haeme and this interac-
tion negatively affects its in vitro DNA-binding ability (
Hernández, Peleato,
Fillat, & Bes, 2004
). Footprinting assays using
furA
and flavodoxin pro-
moters led to the identification of the first experimentally defined binding
sites for a cyanobacterial FurA protein. These Fur boxes consist of arrays
of A/T-rich sequences that show a faint homology with the
Escherichia
coli
consensus sequence. Furthermore, experimental work suggests that, in
addition to proper A/T arrays, DNA conformation might be an important
factor in FurA target recognition and binding (
González, Bes, Peleato, &
Fillat, 2011
). These features are somewhat different from the DNA-binding
properties found for the other cyanobacterial Fur paralogues (
Hernández,
López-Gomollón, Bes, Fillat, & Peleato, 2004
;
López-Gomollón et al., 2009
;
Napolitano et al., 2012
).
3.1.2. Occurrence and functions of Fur paralogues in cyanobacteria
The isolation of a
fur
gene in
Synechococcus
PCC 7942 through an
E. coli
-based
in vivo repression assay was the first evidence of the existence of a Fur pro-
tein in cyanobacteria (
Ghassemian & Straus, 1996
). In this cyanobacterium,
deletion of
fur
resulted in meridiploids that showed iron-deficiency symp-
toms in iron-replete medium, as well as partial derepression of flavodoxin
and of hydroxamate siderophores. Advances in whole genome sequenc-
ing of diverse cyanobacterial strains allow identification of this essential
fur
gene as Synpcc7942_0987. Moreover, searching for ORFs exhibiting the
His-rich motif characteristic of Fur proteins across the 39 cyanobacterial
genomes available in the cyanobase (
http://genome.kazusa.or.jp/cyanobase
)
(
Nakamura, Kaneko, Hirosawa, Miyajima, & Tabata, 1998
) reveals the pres-
ence of several Fur paralogues in all the strains sequenced to date. Although
three Fur-like proteins are commonly found in most cyanobacteria, some
