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four additional genes for response regulators) are also represented in the plasmids pCC7120 α, β,
δ and ε in
Anabaena
sp. strain PCC 7120. Another unique feature of
Anabaena
sp. strain PCC 7120
genome is the presence of proteins with 4 or more repeating units of ~31 amino acids containing
tryptophan and aspartic acid (WD). Proteins with WD repeats are known in eukaryotes (
Arabidopsis
thaliana-
59 genes;
Caenorhabditis elegans
-88 genes;
Saccharomyces cerevisiae
-58 genes) but these are
earlier reported only in case of
Synechocystis
sp. strain PCC 6803 (5 genes). There are 20 such genes
on the chromosome of
Anabaena
sp. strain PCC 7120 and four on the plasmids. These have 4 to
15 WD repeats. The presence of conserved regions of serine/threonine kinases at the N-terminal
regions of three genes (
all0438
,
alr3119
and
all3169
) and the gene products of
alr0029
,
alr2800
and
alr7129
exhibiting similarity to proteins of plant-disease resistant genes signifi es that
Anabeana
sp.
strain PCC 7120 shares a eukaryotic signalling pathway (Kaneko
et al
., 2001). Zhang
et al
. (2007)
conducted a genome-wide survey of Ser/Thr kinase genes in 21 species of sequenced cyanobacterial
genomes. This constitutes the fi rst detailed study on the diversity, conservation, domain structure
and evolution of Ser/Thr kinases in cyanobacteria. The Ser/Thr kinase genes are absent in four of
the
P
.
marinus
strains (CCMP1375, CCMP1986, MIT9312 and NTL2A) and one
Synechococcus
strain
(WH8102). The number of Ser/Thr kinase genes varied greatly from lowest one (in
P
.
marinus
MIT9313
and three
Synechococcus
strains CC9311, CC9605 and CC9902) to 56 (
N
.
punctiforme
PCC 73102). A
phylogenetic tree constructed on the basis of 16S rRNA sequence analysis and distribution of Ser/
Thr genes is presented in Fig. 13. The 286 homologous Ser/Thr kinase genes have been divided into
Total
Proteins
Total
STKs
Additional
domains
Acronym
Key Feature
Anabaena
PCC7120
100
Filamentous freshwater
Filamentous soil
Filamentous symbiont
Filamentous marine
Unicellular freshwater
Unicellular marine
Unicellular marine
Unicellular marine
Unicellular marine
Unicellular marine
Unicellular marine
Unicellular marine
Unicellular marine
Unicellular marine
Unicellular marine
Unicellular freshwater
Unicellular freshwater
Unicellular hot spring
Unicellular hot spring
7120
6214
48(0.77%)
27(56.3%)
100
Anabaena
variabilis
ATCC 29413
Ava
5746
53(0.92%)
25(47.2%)
87
Npun
7364
56(0.76%)
27(48.2%)
Nostoc punctiforme
PCC73102
100
Trichodesmium erythraeum
IMS101
Tery
4759
40(0.84%)
31(77.5%)
Synechocystis
sp. PCC6803
6803
3564
7(0.20%)
2(28.6%)
97
86
Crocosphaera watsonii
WH8501
Cwat
5967
28(0.47%)
5(17.9%)
Prochlorococcus marinus
CCMP1986
1986
1716
-
-
62
Prochlorococcus marinus
MIT9312
9312
1808
-
-
93
Prochlorococcus
NTL2A
NTL2A
1894
-
-
97
Prochlorococcus marinus
CCMP1375
1375
1882
-
-
Prochlorococcus marinus
MIT9313
9313
2273
1(0.04%)
-
100
Synechococcus
sp. CC9605
96
9605
2695
1(0.04%)
-
67
Synechococcus
sp. CC9902
9902
2321
1(0.04%)
-
Synechococcus
sp. WH8102
8102
2526
-
-
94
98
Synechococcus
sp. CC9311
9311
2892
1(0.03%)
-
Synechococcus
elongatus
PCC6301
6301
2527
5(0.20%)
1(20.0%)
100
Synechococcus
elongatus
PCC7942
7942
2662
5(0.20%)
1(20.0%)
100
Synechococcus
sp. JA-2-3Ba(2-13)
CYB
2862
8(0.28%)
2(25.0%)
90
Synechococcus
sp. JA-3-3Ab
CYA
2760
8(0.29%)
3(37.5%)
Gloeobacter violaceus
PCC7421
Unicellular rock
7421
4430
14(0.32%)
3(21.4%)
77
Thermosynechococcus elongatus
BP1
Unicellular hot spring
TBP1
2475
10(0.40%)
4(40.0%)
Figure 13:
Phylogenetic tree of the sequenced cyanobacterial strains and STK information. A phylogenetic tree for
21sequenced cyanobacteria constructed based on 16s rRNA is shown here. Numbers appearing at the nodes corresponded
to the values produced by bootstrap analysis (1000 replicates). Names of marine nitrogen-fi xing strains are marked in grey
boxes. Filamentous diazotrophic strains capable of heterocyst differentiation are marked in bold. Percentages in brackets
represent total STKs as a percentage of total proteins and total additional domains as a percentage of total STKs. With the
kind permission of S. Qin, Ocean University of China, Yushan Road, Qingdao, China [Zhang
et al
. (2007)
BMC Genomics
8:
395; doi:10.1186/1471-2164-8-395].
