Biology Reference
In-Depth Information
regulated by LexA in
E
.
coli
, only
uvrD
has the LexA-binding sites in
P
.
marinus
MIT 9312. Apart from
the SOS-responsive genes, LexA is known to regulate other photosynthetic genes such as PSII reaction
center proteins PsbY (in
A
.
variabilis
ATCC 29413,
A
.
marina
MBIC11017, strains of
P
.
marinus
AS9601,
MIT9215, MIT9301, MIT9312 and MIT9515), CP47 (in
Synechocystis
sp. strain PCC 6803) and a protein
involved in PSI (in
M
.
aeruginosa
NIES-843,
P
.
marinus
strains MIT9312, NATL2A,
Synechococcus
sp. PCC 7002). In addition, 20 genes encoding transporters have been predicted to possess LexA-
binding sites (in case of
A
.
marina
MBIC 11017,
A
.
variabilis
ATCC 29413,
M
.
aeruginosa
NIES-843,
N
.
punctiforme
PCC 73102,
Anabaena
sp. strain PCC 7120,
P
.
marinus
strains MIT9215, MIT9303, MIT9515,
Synechococcus
sp. strain WH8102 and
Synechocystis
sp. strain PCC 6803). Among these, the toxin and
antibiotic exporter genes of
A
.
variabilis
ATCC 29413 and the genes for major drug effl ux transporter in
P
.
marinus
(strains AS9601, MIT9301, MIT9515) and
Synechococcus
sp. strain WH 8102 stand out as
importantly LexA-regulated. The overall conclusion is that at least in
Synechocystis
sp. strain PCC
6803 LexA no longer regulates SOS response (Li
et al
., 2010).
c) Circadian clock proteins
:
S. elongatus
PCC 7942 is the model organism for the studies on the
circadian clock (see Chapter 6 on Circadian rhythms). Nakamura
et al
. (2002) identifi ed genes
kaiA
(
tlr0481
),
kaiB
(
tlr0482
),
kaiC
(
tlr0483
),
sasA
(
tlr0029
)
,
cikA
(tll0899),
pex
(
tlr1955
) and
cpmA
(
tll1189
)
in
T
.
elongatus
BP-1.
A homologue of
pixJ1
( tll0569; that encodes bacteriophytochrome) required
for positive phototaxis,
cikA
(
tll0899
) gene, two genes for fl avin-binding cytochrome-like proteins
(
tll0552
and
tll0425
) and one phototropin gene (
tll1282
that encodes fl avin-binding photoreceptor)
are also present in the genome of
T
.
elongatus
BP-1. KaiA, KaiB and KaiC protein encoding genes
(
kaiA
,
kaiB
and
kaiC
) are absent in
G
.
violaceus
PCC 7421 Of the known input modifi ers
sasA
,
cikA
,
ldpA
and
pexA
only
ldpA
gene sequence is present. Two output modifi er genes (
rpoD2
and
cpmA
) also
have been identifi ed (Nakamura
et al
., 2003). In the genome of
Anabaena
sp. PCC7120, major genes
encoding KaiA, B and C proteins, as also of the genes of the input pathway (
cikA
and
pex
) and output
modifi er proteins (
rpoD2
and
cpmA
) and activator of KaiABC expression (
sasA
) have been identifi ed
(Kaneko
et al
., 2001). All genes governing circadian rhythms are present in
M
.
aeruginosa
PCC 7806.
However, the existence of genes encoding light-regulated two-component system consisting of
cph1
(for phytochrome) and its response regulator (
Rcp1
) in this organism is a question that needs to be
investigated as to which of these processes gains control over the other (Frangeul
et al
., 2008).
7) DNA replication, recombination and repair
:
Kaneko
et al
. (1996) identifi ed inteins (intervening
protein sequences that are excised during post-translational modifi cation) in the genes governing
DNA synthesis in
Synechocystis
sp. strain PCC 6803. Four intein sequences have been identifi ed in the
genes of DNA helicase (
dnaB
), a subunit of DNA polymerase III (
dnaX
), DNA gyrase B subunit (
gyrB
)
and the alpha subunit of DNA polymerase III (
dnaE
). In
Anabaena
sp. strain PCC 7120, two copies
of
dnaB
are present, distributed one each on the chromosome (
all0578
) and the plasmid pCC7120C
(
all7274
). An intein of 429 amino acid residues is present only in the former.
dnaE
gene is split into
two parts (
all3578
and
alr1054
) separated by a 3 Mb portion and these two encode N-terminal and
C-terminal portions, respectively of DnaE protein (Kaneko
et al
., 2001). In
T
.
elongatus
BP-1, two
split
dnaE
genes (
tll2056
and
tll2069
) are separated by a 10.2 kb region in the chromosome that are
suspected to encode N-terminal and C-terminal parts of the DnaE protein, respectively. In addition,
genes for natural transformation (
comA
,
comE
,
comM
) and for genetic recombination (
recA
,
recF
,
recG
,
recJ
and
recQ
) have been identifi ed in this organism (Nakamura
et al
., 2002).
P
.
marinus
strain MED4
lacks genes for several DNA repair pathways including recombinational repair (
recJ
and
recQ
) and
damage reversal gene (
mutT
). The loss of
mutY
gene (the product of which removes adenosines
incorrectly paired with oxidatively damaged guanine residues) in this organism is suggested to be
