Biology Reference
In-Depth Information
Figure 4.6
A. Organization of the operons encoding cyanobacterial metal-regulated
SmtB repressors. Genes encoding metalloregulators (dotted arrows), ATPase genes
(grey arrows) and genes encoding metallothioneins (white arrows) are represented.
Black arrows indicate the imperfect inverted repeats where the SmtB regulators are
bound. (
1
(
Erbe et al., 1995
);
2
(
Thelwell et al., 1998
);
3
(
Liu et al., 2004
);
4
(
Liu et al., 2005
)).
B. Alignment of the DNA-binding sites containing the 12-2-12 inverted repeat sequences
from the operons controlled by cyanobacterial SmtB metalloregulators. The conserved
sequence TGA which is supposed to be in contact to the regulators is underlined.
See the colour plate.
3.4.3. Functions of SmtB proteins
In the absence of zinc,
Synechococcus
SmtB is bound to a specific region
of the
smt
operon, repressing the divergent transcription of both itself
and the gene s
mtA
encoding the metallothionein SmtA (
VanZile, Chen,
& Giedroc, 2002a
). When metal availability increases, two zinc ions are
bound to the α5 site in the homodimer triggering transcription until no
zinc is left to bind to newly synthesized SmtB and repression is again
effective.
Synechococcus smtA
mutants exhibited a fivefold reduction in zinc
