Biology Reference
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photosynthesis was associated with inhibition of nitrate reduction in nitrate supplemented cultures
compared to nitrogen-fi xing cultures. The expression of
groEL
was independent of the nitrogen
status of the medium and readily expressed in response to heat shock but the expression of
cpn60
very much depended on the ability of the organism to utilize nitrate or ammonium ions (Rajaram
and Apte, 2008).
The genome of
Synechocystis
sp. strain PCC 6803 has four
dnaJ
genes (
sll1666
,
sll1933
,
sll0093
and
slr0897
) whereas
P. marinus
MIT9313 and MED4 possess three and two
dnaJ
homologues, respectively.
However, the homology and organization of the
dnaJ
genes differed in these organisms. While
dnaJ3
shared the strongest identity (about 60% identity) between
Synechocystis
sp. strain PCC 6803 and
P.
marinus
MIT9313,
Prochlorococcus
dnaJ1
is not well conserved (that showed only 34% identity). In
both the
Prochlorococcus
strains
dnaJ1
is located close to
dnaK3
gene. Under high light exposure, the
mRNA of
dnaJ3
dramatically increased in
Synechocystis
and
P. marinus
MIT9313 (Mary
et al
., 2004).
The Hsps have been employed to measure evolutionary relationships among eubacterial groups.
In this connection, sequence comparisons of GroEL from different bacterial species (resulted into
phylogenetic trees based on distance or parsimony methods that were consistent with 16S rRNA
trees) were resolved into different clusters of proteobacteria, chlamydiae, bacteroids, spirochaetes,
fi rmicutes (gram-positive bacteria), cyanobacteria and chloroplasts. Detailed analyses suggested that
the GroEL proteins serve as valuable evolutionary tools to draw phylogenetic relationships among
eubacteria (Viale
et al
., 1994). In a similar manner, coding region of of
cpn60
(GroEL or Hsp60) can
be amplifi ed with universal PCR primers. A cpn60 sequence database (consisting of more than 2000
such sequences from more than 240 genera of bacteria, eukaryotes and archaebacteria available
at http://cpndb.cbr.nrc.ca) has been created that is useful in clinical, phylogenetic and microbial
ecology studies ( Hill
et al
., 2004).
ii) Expression of dnaK genes
:
Nimura
et al.
(1994a) identifi ed three
dnaK
homologues
dnaK1
,
dnaK2
and
dnaK3
in
S. elongatus
PCC 7942. In contrast to DnaK1 and DnaK2 proteins that are present
in the cytosol, DnaK3 protein is present in large amounts associated with thylakoid membranes.
Characteristically, DnaK3 possessed a long C-terminal region, the deletion of which did not cause
any alteration in the phenotype of the generated strain when compared to wild-type (Nimura
et al
.,
1994b, 1996). The genome of
Synechocystis
sp. strain PCC 6803 revealed the presence of four
dnaK
homologues (ORFs
sll0086
,
sll0170
,
sll1932
and sll0058; Kaneko
et al
., 1996; Mary
et al.
, 2004) that
showed high degree of homology to
S. elongatus
PCC 7942
dnaK
homologues. DnaK3 protein of
Synechocystis
sp. strain PCC 6803 also showed a long C-terminal region resembling the DnaK3 of
S.
elongatus
PCC 7942. The presence of three
dnaK
homologues has been demonstrated in the genome of
Anabaena
sp. strain PCC 7120 (http:www.kazusa.or.jp/cyano),
P. marinus
MIT9313 and MED4 strains
(Mary
et al
., 2004). The presence of three
dnaK
homologues is a rare feature among prokaryotes as
only two
dnaK
homologues (
hsc62
and
hsc66
; of these the latter is induced by cold shock but not by
heat shock) were reported in
E
.
coli
other than
dnaK
(Seaton and Vickery, 1994; Lelivelt and Kawula,
1995; Yoshimura
et al
., 1998) and
in
Borrelia burgdorferi
B21 two
dnaK
homologues are present (Fraser
et al
., 1997).
Circadian control of
dnaK
gene expression in
Synechocystis
sp. strain PCC 6803 was monitored by
using the promoterless bacterial luciferase genes (
luxAB
from
Vibrio harveyi
) as a reporter gene. The
luxAB
gene set was introduced downstream of the promoter region of
dnaK
gene of
Synechocystis
. The
dnaK
gene expression pattern oscillated with a period of 22 hr for at least 5 days in continuous light.
The bioluminescence rhythm satisfi ed the three criteria set for circadian rhythms. Simultaneously,
the mRNA levels of
dnaK
gene also oscillated in a rhythmic manner suggesting that the expression
