Biology Reference
In-Depth Information
In a recent study (
Napolitano et al., 2012
), FurB has been identified as a
Zur regulator in
Anabaena
PCC 7120. Unlike most FurA-modulated genes
that exhibit two or more iron boxes, specific binding of FurB to DNA
occurs in the single 7-1-7 consensus motif (TGATAATNATTATCA). In
Anabaena
PCC 7120, FurB is involved in the control of at least 23 genes,
17 of them organized in six operons. FurB-controlled genes fall into four
different categories, namely paralogues of zinc metalloproteins, putative
metallochaperones, components of ABC transporters and outer membrane
proteins (
Table 4.3
).
These data indicate that FurB/Zur is a main component, together
with SmtB proteins (
Huckle, Morby, Turner, & Robinson, 1993
;
Thelwell,
Robinson, & Turner-Cavet, 1998
), in the response and adaptation of cya-
nobacteria to Zn
2+
deficiency and suggests that FurB might be a moon-
lighting protein, playing a dual role in
Anabaena.
3.1.2.4. FurC: a potential regulator of regulators
A third Fur paralogue, FurC (Alr0957), has been identified and purified in
Anabaena
PCC 7120 (
Hernández, López-Gomollón et al., 2004
). The FurC
basal expression level is lower than those of FurA and FurB and exhibits a
significant gap in homology with those proteins. As other members of this
family, FurC is able to dimerize although the dimer is only detected under
oxidizing conditions. Our hypothesis is that FurC can form heterodimers
through its C-terminus with other Fur family members, modifying their
affinity for DNA. Residues involved in C-terminal domain dimerization
are quite conserved in FurC, allowing the potential formation of heterodi-
mers. Reverse genetics studies are expected to rule out that FurC can have
another role, so far unknown, including target promoters not yet identified.
3.1.3. Deciphering the FurA regulon
The potentially essential role of FurA in
Anabaena
sp. physiology poses the
challenge of deciphering its regulon. Comparative global analyses of tran-
scriptomes and proteomes for
fur
deletion mutants and their parental wild-
type strains have been traditionally used to characterize Fur regulons in
several heterotrophic bacteria (
Baichoo, Wang, Ye, & Helmann, 2002
;
Gao
et al., 2008
;
McHugh et al., 2003
;
Wan et al., 2004
). However, gene knock-
out cannot be used to define function when silencing implies death. In such
cases, alternative approaches such as overexpression (
Olmedo-Verd, Flores,
Herrero, & Muro-Pastor, 2005
;
Wu, Liu, Lee, & Golden, 2004
) or selectively
regulating gene expression (
Callahan & Buikema, 2001
;
Zhang et al., 2000
)
