Chlamydomonas
633
Stability
Processing
Splicing
Assembly
and
integration
Translation
RNA
Thylakoids
70S
80S
mRNA
Nuclear DNA
mRNA
80S
Chloroplast
DNA
Fig. 6
Biosynthesis of the photosynthetic apparatus. The nucleus and chloroplast are
shown in the upper and lower parts, respectively; 70S and 80S represent the chloroplast
and cytosolic ribosomes. Synthesis of structural photosynthetic proteins is indicated by
continuous lines. The roles of nuclear-encoded factors in posttranscriptional steps of
chloroplast gene expression are shown by dashed lines.
has been possible to perform targeted
disruptions of several of the smaller pho-
tosystem I and II genes in the chloro-
plast genome of
C. reinhardtii
using the
aad
A expression cassette. It is notewor-
th
yth
a
tmo
s
to
fthe
s
egened
i
s
rup
t
ion
s
have a more drastic effect on the stabil-
ity of the complexes than that of similar
disruptions in cyanobacteria. For exam-
ple, disruption of either the
psbO
or the
psbK
gene in cyanobacteria still allows
for photoautotrophic growth in cyanobac-
teria, but a similar disruption results in
the destabilization of photosystem II in
C. reinhardtii
. Similar differences in the
stability of the photosystem I complex be-
tween
C. reinhardtii
and cyanobacteria have
been observed, with mutants carrying di-
rected, speciĀ±c amino acid substitutions
in the PsaC protein, the apoprotein of
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