Biology Reference
In-Depth Information
An important system for the expression of genes involved in the response
to hypoxia and NO is Dos; it consists of the sensor kinases DosS and DosT
(
Roberts, Liao, Wisedchaisri, Hol, & Sherman, 2004
) and the response reg-
ulator DosR (
Kendall et al., 2004
). These proteins are involved in the
response by
M. tuberculosis
to reactive nitrogen intermediates (
Ohno
et al., 2003
). Perhaps surprisingly,
glbN
was not up-regulated in response
to exposure to 0.005-5 mM DETA/NO for 40 min, and
glbO
was not
up-regulated in response to exposure to 0.05-50 mM H
2
O
2
for 40 min
(
Voskuil, Bartek, Visconti, & Schoolnik, 2011
). Neither
glbN
nor
glbO
has been implicated in the Dos regulon, suggesting that they are regulated
by some other system; however, in a
dosR
mutant,
glbN
was down-
regulated, perhaps suggesting that
glbN
is somewhat controlled by this
system (
Kendall et al., 2004
).
In the case of Ml trHbO, a putative promoter was found and cloned into
a shuttle vector in front of the
lacZ
gene, which was then transformed into
both
M. smegmatis
and
E. coli
. Activity of the LacZ protein, measured using
the
-galactosidase assay, was found in
M. smegmatis
during early and late
exponential phase but not in
E. coli
(
Fabozzi et al., 2006
), suggesting the
absence of some cellular machinery in
E. coli
required for promoter activity.
The promoters for
M. smegmatis glbN
and
glbO
were cloned in the same way
and showed
b
b
-galactosidase activity which was highest in late exponential
phase and increased by NO donors SNP and SNAP; the
glbN
promoter
was activated to a higher extent than the
glbO
promoter. Interestingly,
the
M. leprae glbO
promoter also showed increased activation to SNP and
SNAP, suggesting again that Ml trHbO may be involved in NO detoxifi-
cation (
Fabozzi et al., 2006
). Similar experiments were done with promoters
for
glbN
,
glbO
and
groEL,
a heat shock protein, cloned into
M. smegmatis
.
Cells were subjected to different stresses and the up-regulation of each gene
detected by RT-PCR: exposure to 10-mM sodium nitrite led to the biggest
increase in
glbN
expression, with 30 mM leading to the biggest increase in
glbO
expression (
Joseph, Madhavilatha, Kumar, & Mundayoor, 2012
). In
the absence of any stress, and agreeing with previous data, both promoters
showed increased activity in late exponential phase.
4. CONVENTIONAL AND NOVEL FlavoHbs
OF MYCOBACTERIA
Less is known about the flavoHbs in Mycobacteria. Computational
and sequence analysis of available Mycobacterial genomes and protein data
