Biology Reference
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Pkn D (alr4368; Zhang and Libs, 1998), PknE (alr3732; Zhang
et al
., 1998), PknC (all4813; Gonzalez
et al
., 2001) and Pkn22 (alr2502; Xu
et al
., 2003). Of these, PknC has broad substrate specifi city.
A protein phosphatase 1/2A/2B homologue (
prpA
) has been found 301 bp downstream of
pknE
gene in
Anabaena
sp. PCC 7120. Recombinant proteins produced in
E
.
coli
have been used to
raise polyclonal antibodies against these and are used for immunodetection of the corresponding
proteins under various growth conditions. Though both these genes are closely linked but they are
not expressed together (Zhang
et al
., 1998). PrpA(95 kDa) protein has been found to be expressed
in wild-type cells after nitrogen step-down whereas expression of PknE (53 kDa) protein has been
found be high in nitrate-enriched medium but it decreased on nitrogen step-down up to 3 h after
which it increased on long time exposure in nitrogen-free medium. An Nm resistance cassette has
been used to generate disruptant mutants. ARAs revealed that aerobic and anaerobic nitrogen
fi xation rates have decreased considerably with abnormal heterocyst structure, although there
was no difference in glycolipids of heterocysts (Zhang
et al
., 1998). The involvement of two genes
encoding protein kinases of the HstK family,
pkn44
(
all1625
) and
pkn30
(
all3691
) in the synthesis of
minor heterocyst-specifi c glycolipid in
Anabaena
sp. strain PCC 7120 has been reported by Shi
et al
.
(2007). The double mutant (D4.3) strain revealed a Fox
-
and Hgl
-
phenotype due to which aerobic
nitrogen fi xation and a minor heterocyst glycolipid are absent. D4.3 strain showed a delay of 24 h
in heterocyst formation that was arrested at an early stage due to the absence of minor heterocyst
glycolipid component. They concluded that the synthesis of major and minor Hgls is regulated by
PrpJ and
pkn44
/
pkn30
regulatory pathways, respectively.
PatA encoded by
patA
gene of
Anabaena
sp. PCC 7120 contains 379 amino acids and the
carboxy-terminal domain bears similarity to CheY of
E
.
coli
and other response regulators of the
two-component regulatory systems. A mutant of
patA
differentiates only terminal heterocysts and
exhibits poor growth in nitrogen-free medium compared to wild-type (Liang
et al
., 1992). Cohen
et al
. (1994) isolated and characterized 14 Fox
-
and Sym
+
mutants isolated after transposon Tn5-
1063 insertion mutagenesis of
N
.
punctiforme
ATCC 29133, a symbiont of
A
.
punctatus
. One of the
mutants of this group, UCD311 failed to develop mature heterocysts and fi xed nitrogen under
anoxic conditions though it was capable of synthesizing the heteocyst envelope. Sequence analysis
of the interrupted gene revealed an ORF which has been designated as
devR
(for developmental
regulation). The deduced amino acid sequence of DevR revealed it to be a receiver domain of two-
component regulatory system of
N. punctiforme
ATCC 29133. DevR bears similarity to CheY of
E
.
coli
and SpoOF of
Bacillus
subtilis
and possesses Asp57 as the phosphorylation site
(Campbell
et al
.,
1996). The synthesis of heterocyst envelope polysaccharide of
Anabaena
sp. strain PCC 7120 has
been reported to be under the regulation of
hepK
(
all4496
) that encodes a sensory protein histidine
kinase and
devR
A
(
devR
of
Anabaena
;
alr0442
) that encodes its corresponding cognate response
regulator (Zhu
et al
., 1998; Zhou and Wolk, 2003). Mutation of
hepK
prevented the induction of
hepA
(
alr2835
) as well as envelope polysaccharide. The gene product, Alr2835 resembles a member
of the family of ABC transporters and is essential for the synthesis of Hep layer (Zhu
et al
., 1998).
In
vitro
autophosphorylation [in presence of (γ-
32
P)] and dephosphorylation (in presence of ADP) of
the cytoplasmic portion of HepK and the transfer of phosphoryl group to DevR (of
N
.
punctiforme
ATCC 29133) and DevR
A
have been demonstrated using hexa-histidine tagged to N-terminus of the
recombinant proteins produced in
E
.
coli
(Zhou and Wolk, 2003). Ning and Xu (2004a) identifi ed a
two-component histidine kinase gene (
alr0117
) that may control heterocyst envelope polysaccharide
layer and certain late maturation stages in heterocyst development of
Anabaena
sp. strain PCC 7120.
In a transposon (Tn5-1087b) generated mutant, with its insertion in between nucleotides between 342
and 343 of
alr0117,
the expression of
hepA
was completely blocked while
patB
expression occurred
